Physical Sciences
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Physical Sciences
MATTER AND MATERIALS
Exercise 1: Matter and Classification: The Materials of Which an Object is Composed
Exercise 2: Matter and Classification: Elements and Compounds
Exercise 3: Matter and Classification: Names and Formulae of Substances
Exercise 4: Matter and Classification: Metal, Metalloids and Non-Metals
Exercise 5: Matter and Classification: Thermal Conductors and Insulators
Exercise 6: Matter and Classification: Magnetism
Exercise 7: Kinetic Theory of Matter
Exercise 8: States of Matter and Kinetic Molecular Theory
Exercise 9: The Atom: Basic Building Block of all Matter
Exercise 10: Structure of the Atom: Protons, Neutrons, Electrons
Exercise 11: Structure of the Atom: Isotopes
Exercise 12: Electron Configuration
Exercise 13: The Periodic Table
Exercise 14: Chemical Bonds
WAVES, SOUND AND LIGHT
Exercise
Exercise 16: Transverse
Exercise
Exercise
Exercise
Exercise
MATTER AND MATERIALS (CONTINUED)
Exercise
CHEMICAL CHANGE
Exercise 22: Physical and Chemical Change: Separation of Particle
CHEMICAL CHANGE (CONTINUED)
Exercise 29: Reactions in Aqueous Solution: Interaction and Effects of Ions
Exercise 30: Quantitative Aspects of Chemical Change: Atomic Mass and Mole
Exercise 31: Quantitative Aspects of Chemical Change: Molecular, Formula Masses and Mole
Exercise 32: Quantitative Aspects of Chemical Change: Composition 174
Exercise 33: Quantitative Aspects of Chemical Change: Molar Volume of Gases 175
Exercise 34: Quantitative Aspects of Chemical Change: Concentration 175
Exercise 35: Quantitative Aspects of Chemical Change: Stoichiometric Calculations 177
MECHANICS
Exercise 36: Vectors and Scalars: Definitions
Exercise 37: Vectors and Scalars: Vector Diagrams
Exercise 38: Motion in One Dimension: Position, Displacement and Distance
Exercise 39: Motion in One Dimension: Speed and Velocity
Exercise 40: Motion in One Dimension: Acceleration and Ticker Timer Problems
Exercise 41: Motion in One Dimension: Displacement Versus Time Graphs
Exercise 42: Motion in One Dimension: Velocity Versus Time Graphs
Exercise 43: Motion in One Dimension: Acceleration Versus Time Graphs
Exercise 44: Motion in One Dimension: Equations of Motion
Exercise 45: Energy: Gravitational Potential Energy
Exercise 46: Energy: Kinetic Energy
Exercise 47: Energy: Mechanical Energy
CHEMICAL SYSTEMS
SKILLS FOR PHYSICAL SCIENCES LEARNERS
Scientific Notation
Very large or very small numbers are preferablywritten in the scientific notation, e.g. a charge of 0,0000000326 C can be written as 3,26 x 10–8 C or a pressure of 350625 Pa can be written as 3,51 x 105 Pa.
Notice that in the scientific notation the number is written as a product of two numbers –the first number is between 1 and 10 and the second as 10n.
The first number is usually rounded off to two decimal places.
Please ensure that you know how to multiply and divide by numbers with exponents and how to use your calculator when dealing with exponents.
Conversion of Units
The 7 basic SI units:
Mass(m)is measured in kilogram(kg)
Time(t)is measured in second(s)
Length( )is measured in metre(m)
Electric current(I) is measured in ampere (A)
Amount of substance(n) is measured in mole (mol)
Temperature(T)is measured in kelvin(K)
Luminous intensity is measured in candela (cd)
All answers should be given in SI units,unless otherwise specified.
Mass is often given in gram. In order to convert it to kg, it is useful to know that ‘kilo’ means ‘1000’ or 103
Therefore1 kg = 103 g and 1 g = 10–3 kg.
Time is often given in hours (h). Remember that 1 h is 60 minutes and 1 minute is 60 seconds.
Hence 1 h = 3600 s or 3,6 x 103 s and 1 s = 1/(3,6 x 103) h
Length is sometimes given in millimetre (mm) or centimetre (cm) or decimetre (dm) or kilometre (km).
In order to convert from one to the other, it is useful to understand the following diagram:
For each space that you move to the right, you 10 or x10–1 ,
e.g. 5 mm = 5 x 10–1 cm = 5 x 10–2 dm = 5 x 10–3 m = 5 x 10–6 km, etc.
For each space that you move to the left, you x10,
e.g. 5 m = 5 x 10 dm = 5 x 102 cm = 5 x 103 mm, etc.
If the conversion is for area, which is measured in m2, then for each space that you move to the right, you 102 or x10–2 , e.g. 5 cm2 = 5 x 10–2 dm2
= 5 x 10–4 m2, etc.
For each space you move to the left, you x102, e.g. 6 km2 = 6 x 106 m2, = 6 x 108 dm2 = 6 x 1012 mm2, etc.
If the conversion is for volume, which is measured in m3, then for each space that you move to the right, you 103 or x10–3 , e.g. 250 cm3
= 250 x 10–3 dm3 = 250 10–6 m3, etc.
For each space you move to the left, you x103, e.g. 1 km3 = 1 x 109 m3 = 1 x 1015 cm3, etc.
The scientific temperature scalethat is used inScienceis the kelvin scale, but the celsiusscale is popular for everyday use.In order to convert from celcius to kelvin and vice versa, the following equation can be used:
T = t + 273, where T is the temperature in kelvin and t is the temperature in celcius.
What is Rate?
Rate is the change per second
E.g. power is rate at which work is done or (work done)/second
Current is rate at which charge flows or (amount of charge)/second
Sample
Directly and Inversely Proportional
If we say that a is directly proportional to b, it means that if a doubles, b also doubles; if a increases 10 times, balso increases 10 times, etc.
This is written asa b, which we read as “a is directly proportional to b”.
To change this into a mathematical equation, we write it as a = kb,where k is a constant.
Example:
This means that it we measure the distance covered by different people for the same time, say 10 s, then the greater the speed of the person, the greater the distance covered by the person.
D v, which can be written as D = kv, where the constant k is the time –the equation becomes
The graph of two quantities that are directly proportional,is always a straight line passing through the origin.
If we say that p is inversely proportional to q, it means that if p increases 2 times, q decreases 2 times; if p increases 10 times, q decreases 10 times, etc.
This is written as p 1/q, which we read as “p is inversely proportional to q”.
To change this into a mathematical equation, we write it as p = k/q, where k is a constant.
The graph for two quantities that are inversely proportional is a hyperbola.
Ratios
In Physical Sciences we are often requiredto divide a quantity into ratios.
Supposethree workers, X, Y and Z divide the profit of a business in a ratio of 1:3:5.
This means that for every R1 that X earns, Y earns R3 and Z earns R5, i.e. every R(1 + 3 + 5) = R9 is split up into R1, R3 and R5. Hence X earns 1/9 of the profit, Y earns 3/9 of the profit and Z earns 5/9 of the profit.
Now it easy to calculate each one’s share for any profit, e.g. if the profit is R1800, X earns 1/9(R1800) = R200; Y earns 3/9(R1800) = R600 and Z earns 5/9(R1800) = R1000
Example: A potential difference of 24 V dividesin a ratio of 2:2:4 across resistors P, Q and R.
Share of potential difference for P: 2/(2 + 2 + 4) = 2/8 2/8(24 V) = 6 V
Share of potential difference for Q: 2/(2 + 2 + 4) = 2/8 2/8(24 V) = 6 V
Share of potential difference for R: 4/(2 + 2 + 4) = 4/8 4/8(24 V) = 12 V
Practical Investigations
The investigative question should always relate the two quantities investigated, e.g. suppose we investigate the relationship between temperature and volume, then the question can be “What is the relationship between temperature an volume?” or “Does volume increase with temperature?”, etc.
The hypothesis should be an answer on the investigative question, e.g. “Volume is directly proportional to temperature” or “Volume increases as temperature increases”, etc. The hypothesis may be a wrong statement, but it has to answer the investigative question.
The results should be recorded in a table with suitable headings that contain units, e.g. the column that gives the temperature should have the heading “Temperature (°C)” and the column containing the volume should have the heading “Volume(cm3)”.
Electric current is sometimes indicated as micro ampere ( A) or milli ampere (mA).
‘Micro’ means one millionth, or 10–6 and ‘milli’ means one thousandth, or 10–3
The independent variable is the quantity that you control –suppose you decide you are going to take the volume at 0 °C, 10 °C, 20 °C, then temperature is the independent variable.
The dependent variable is the quantity that changes because of thechange in the one that you control –in this case, the volume.
The constantvariables are those quantities that you will have to keep the same in order to have a fair investigation, i.e. you cannot have anything that will influence your readings except your two variables. E.g. you will have to work with the same substance –you cannot use hydrogen in one measurement and then iron in the next. You will also have to keep the mass of the substance constant –you cannot take 10 g of hydrogen in one measurement and 50 g of hydrogen in the next. You will also have to keep the pressure constant –one measurement cannot be taken at sea level and the other at high altitudes, etc. The graph should always have the two axes labelled properly, similar to the table, includingunits and then also a proper scale.
Theindependent variable should always be on the horizontal or X-axis and the dependent variable on the vertical or Y-axis.
The conclusion should state the relationship between the two variables.
Precautions have to be taken to exclude dangers and factors which could cause the investigation to fail.
A quantitative analysis involves measurements, e.g. when you determine the relationship between the volume of a gas and temperature, you have to measure temperature and volume.
A qualitative analysis involves a study, e.g. when you determine which materials conduct electricity; you only change the substances and observe in which cases the light bulb glows.
Graphs: Gradient and Area
In both Chemistry and Physics you will come across many graphswhich you will have to interpret. At this stage there are two important skills to master that come in very useful: Lookat the gradient of the graph and the area included by the graph and the axes. In any graph the .This means, the gradient will be whatever is on the Y-axis divided by whatever is on the X-axis.
Now look for an equation on the data sheet that contains the two variables, v and t, and see if you can rewrite the equation in such a way that v and t are the subject –the rest of the equation then represents the gradient. In our example we find a = represents a. Whateverthe gradient does, acceleration a does the same –the first part of the graph has a constant and negative gradient, hence the acceleration a will be constant and negative. In the second part of the graph the gradient is constant and positive; hence the acceleration is constant and positive. In any graph the area included by the graph and the axes is calculated as length times width. In our example it is v x t. Again see if you can find an equation that you can rearrange in such a way that it gives vt i
MATTER AND MATERIALS
Matter and Classification: The Materials of Which an Object is Composed
Matter is anything that occupies space and has mass.
Matter can be classified in various ways. In thischapter welook at different ways of classifying matter.
Matter can be classified by its properties.
The physical properties of a substance are those properties that can change without changing the chemical composition of the substance.
The physical properties of materials that you studied in grade 9 are:
Strength
Thermal conductivity(how well it conducts heat)
Electrical conductivity
Brittle(crumbles when hammered), malleable(can be hammered into thin sheets)orductile(can be drawn intoa thin wire).
Magnetic or non-magnetic
Density(ratio of mass to volume or d = m/V)
Melting and boiling points
Matter and Classification: Mixtures
A mixture of matter can also be classified by the kind of mixture it is.
Properties of a mixture:
The components of the mixture can be in any ratio.
The properties of each of the components are retained.
The components can be separated by physical means (e.g. a mixture of sulphur and iron filings can be separated by means of a magnet).
A homogeneous mixture has particles of uniform composition and therefore in the same phase, i.e. you cannot distinguish two different layersor phases, e.g. air, ink and brine (salt water).
In homogenised milk the fatty particles are broken to be of uniform size, resulting inlittle separation of milk and cream.(‘homo-‘ means ‘same’.)
A heterogeneous mixture has particles of non-uniform composition and thus in different phases or similar phases that do not mix (e.g. water and oil).(‘hetero-‘ means ‘different’)
Exercise 1:
1Give ONE word/term for
1.1a mixture in which the particles are of uniform composition. (1)
1.2a mixture that has particles which are in different phases. (1)
1.3a solution in which all components are in the same phase. (1)
1.4 the type of properties under which melting points, boiling pointsand densities are classified.(1)
1.5the type of mixture under which salt water can be classified. (1)
1.6the physical property that explains why oil floats on top of water (1)
2Classify each of the following substances as a homogeneous mixture or a heterogeneous mixture Explain your choice in each case.
2.1Tapwater 2.2Blood
2.3Food colouring and water
2.5Mixture of sand and water
2.7Iodine dissolved in ethanol
2.4Grapejuice
2.6Coffee
Method C:Separation of sulphur and iron filings by using a magnet
Method D:Evaporation of a sodium chloride solution
Method E:Separation of a water-sunflower oil mixture by using a separating funnel
3.1Are the separation methods above physical or chemical processes? Explain. (2)
3.2List THREE essential pieces of equipment that you will use to carry out method A. (3)
3.3Consider method B:
3.3.1What phase change occurs when a substance boils? (1)
3.3.2Does condensation require heating or cooling? (1)
3.3.3Which compound has the strongest intermolecular forces –water or ethanol?
Give a reason for your answer. (2)
Sample
2.8Iodine that does not dissolve in water (16)
3It is sometimes necessary to separate mixtures into their components. Below are five examples of separation techniques.
Method A:Filtering of a sand-water mixture
Method B:Distillation of a water-ethanol mixture to remove water. Ethanol boils at 78 ºC and water at 100 ºCat sea-level. Distillation is the process by which a liquid solution is heated to produce a vapour which is then condensed.
3.3.4On which property of compounds does distillation depend? (1)
3.3.5A certain whiskey is triple distilled. Why would consumers of alcohol find this attractive?(1)
3.4Write the balanced chemical equation for the reaction when a mixture of sulphur and iron filings is heated to produce iron(II) sulphide. (2)
3.5Write down the chemical formula for sodium chloride. (1)
3.6Consider method E:
The sunflower oil has a lower density than water.
3.6.1Which liquid forms the top layer in the water-sunflower oil mixture? (1)
3.6.2Which liquid will have the higher mass: 250 m water OR 250 m of sunflower oil?
Explain the answer. In your explanation, make use of the definition of density.(4)
3.7Classify each of the following mixtures as heterogeneous or homogenous:
3.7.1Sand and water (1)
3.7.2Ethanol and water (1)
3.7.3Water andsunflower oil (1)
3.8Consider method C:
Which property of the components in this mixture makes the separation method described possible? (2)
4A learner investigates the separation of mixtures into separate components.
During his investigation he comes across the terms and separation techniques shown in the table.
Terms Separation techniques
Compounds
Pure substances
Homogeneous mixtures
4.1Define each of the following terms:
Evaporation
Distillation
Filtration
Magnetic separation
Crystallisation
4.1.1Pure substance (2)
4.1.2Homogeneous mixture (2)
4.2Give an example of a:
4.2.1Pure substance (1)
4.2.2Homogenous mixture (1)
4.3The learner writes the following statement in his exercise book:
Metals and non-metals are compounds.
Classify this statement as TRUE or FALSE. (2)
4.4From the list of separation techniques in the above table, choose the technique that will best separate each of the following mixtures:
4.4.1Oil and water (1)
4.4.2Copper and steel nails (1)
4.4.3Sugar and water (1)
4.4.4Water and alcohol (1)
4.5Which ONE of the methods listed in the table above will you use to separate sand and sugar?
Briefly describe the steps that you will follow during this separation. (4)
Matter and Classification: Pure Substances: Elements and Compounds
A pure substance is an element or compound with definite composition.
Pure matter can be classified as elements and compounds
Elements and compounds can be represented microscopically as shown in the diagrams:
An element is a substance that cannot be broken down into simpler substances, i.e. it is made of only one kind of atom.(Diagrams1 and2).
1Give ONE word/term for
1.1more than one type of compound mixed together. (1) 1.2a substance that is made of only one kind of atom. (1) 1.3a chemical combination of two or more different elements. (1) 1.4a composition of two or more atoms that act as unit. (1)
Element consisting of single atoms
Element consisting of molecules of the same atoms
Compound consisting of molecules made up of different atoms
Note that some elementsexist as single atoms(diagram 1)and some exist only as molecules of the same atoms (diagram 2).
A compound is a chemical combination of two or more different elements(diagram 3), i.e. it can be broken down chemically into two or more different elements. Please note that if that more than one element combine, the result is a compound But if more than one atom combine, the result is a molecule.
From the diagram above onecan see that a compound consists of a collection of molecules, which are made up of different types of atoms.
An element consists of a collection of identical atoms or molecules made up of identical atoms. A pure substance consists of only one type of atom (i.e.one element), e.g. sulphur (S)as in diagram 1 oroxygen (O2)as in diagram 2, etc. OR one type of compound, e.g. only water (H2O) or only hydrochloric acid (HC ),as in diagram 3,etc.
An impure substance consists of more than one type of atom mixed together, e.g. iron (Fe) andsulphur (S) ornitrogen (N2) and oxygen (O2), etc. OR more than one type of compound mixed together, e.g. brine, which issalt (NaC ) in water (H2O) orsoda water, which iscarbon dioxide (CO2) in water. The purity of a substance can be determined by using its physical properties, e.g. by determining whether itsboiling or melting pointorits density, etc.is what it is supposed to be. For example, the density of pure water is 1 g cm-3. If however we find that the density of a sample of water is greater than 1 g cm-3, one can assume that the water is impure –something is dissolved in the water. It can also be determined whether a substance is pure by trying to separate it into different components, e.g. using chromatography.
Chromatography can e.g. be usedin the following wayto show that watersoluble ink isa mixture of colours:
Cut filter paper into strips and draw a bold linewith each ink colour pen on a separate strip about 5 cm from the top of the strip. Place the top of the strips in a beaker filled with water and allow the strips to hang down the outside of the beaker. After a while the single colour will separate into different colours, because the particles of different colours have different sizes, resulting in the smaller particles moving faster through the filter paper and the larger particles staying behind.
What we have learned so far can be summarised in the following diagram:
2Water can be classified as a/an Aelement. Bcompound.
Sample
Chomogeneous mixture. Dheterogeneous mixture. (2)
3Which ONE of the following is NOT an element?
4Which of the following statements is/are correct?
IAll elements consist of single atoms. IISome elements consist of molecules. IIIAll compounds consist of molecules.
5Which of the following substancesare pure substances?Give a reason for your answer in each case.
5.1Seawater 5.2Tea 5.3Table salt 5.4Copper 5.5Brass 5.6Air 5.7Nitrogen 5.8Steel 5.9A softdrink such as Coca Cola. (16)
Matter and Classification: Names and Formulae of Substances
Elements Compounds Homogeneous mixtures Heterogeneous mixtures
Matter can also be classified by its name, e.g. the carbonates, the sulphates, the hydroxides, etc. The Periodic Table (see in back of book)lists the elements known to man. The elementsare arranged in order of increasing atomic number or number of protons. Each column is called a group and the elements in the same grouphave similar chemical properties. Each row iscalleda period.
You should at least know the names and symbols of the following elements:
SymbolNameSymbolNameSymbolNameSymbolName HHydrogenNeNeon KPotassiumSnTin HeHeliumNaSodiumCaCalciumIIodine LiLithiumMgMagnesiumMnManganeseBaBarium BeBerylliumA AluminiumFeIronPtPlatinum BBoronSiSiliconNiNickelAuGold CCarbonPPhosphorousCuCopperHg Mercury NNitrogenSSulphurZnZincPbLead OOxygenC ChlorineBrBromine FFluorineArArgonAg Silver
The scientific name of a compound indicates the names of the elements from which it is made, e.g.: Hydrogen chloride (HC )is made up of hydrogen(H)and chlorine(C ) Calcium oxide (CaO) is made up of calcium (Ca) and oxygen (O), etc.
Metals are always named first, followed by the non-metal, e.g. magnesium oxide (MgO).
In the case of two non-metals, the element to the left on the Periodic Table is named first, e.g. silicon dioxide (SiO2) andhydrogen bromide (HBr).
If the two non-metalsare in the same group, the one lower down is named first, e.g. sulphur dioxide (SO2).
Diagram 1 Diagram 2 Diagram 3
Anions are negatively charged ions. They always form the last part of the molecule. The following table of anions will be provided:
fluoride F- oxide O2chloride C - peroxide O22bromide Br- carbonate CO32iodide I- sulphide S2hydroxide OH- sulphite SO32nitrite NO2- sulphate SO42nitrate NO3- thiosulphate S2O32hydrogen carbonate HCO3- chromate CrO42hydrogen sulphite HSO3- dichromate Cr2O72hydrogen sulphate HSO4- manganate MnO42dihydrogen phosphate H2PO4- oxalate (COO)22-/C2O42hypochlorite C O- hydrogen phosphate HPO42chlorate C O3- nitride N3permanganate MnO4- phosphate PO43acetate (ethanoate) CH3COO- phosphide P3-
Note that the suffix ‘-ate’ indicates the presence of oxygen atoms. Carbonate is made up of carbon and oxygen, sulphate is made up of sulphur and oxygen, nitrate is made up of nitrogen and oxygen and phosphate is made up of phosphorous and oxygen.
The suffix ‘-ite’ is also used to indicate the presence of oxygen, but one oxygen atom less than the corresponding ‘-ate’, e.g. sulphate is SO4 2-, but sulphite is SO3 2-, nitrate is NO3 -, but nitrite is NO2 -
The ‘-ide suffix is used when a cation (positive ion, which could be a metal, hydrogen or NH4+ ion) is bonded to a monatomic anion (anion made up of just one type of atom), e.g. hydrogen sulphide (H2S), sodium chloride (NaC ), carbon dioxide (CO2), etc.
The only exception is the hydroxide ion (OH-), e.g. sodium hydroxide (NaOH).
Cations arepositively chargedions and they form the first part of a molecule.
The following table of cations will be provided:
hydrogen H+ beryllium Be2+ aluminium A 3+ chromium(VI) Cr6+
lithium Li+ magnesium Mg2+ chromium(III) Cr3+ manganese(VII) Mn7+
sodium Na+ calcium Ca2+ iron(III) Fe3+
potassium K+ barium Ba2+ cobalt(III) Co3+
silver Ag+ tin(II) Sn2+
mercury(I) Hg+ lead(II) Pb2+
copper(I) Cu+ chromium(II) Cr2+ ammonium NH4+ manganese(II) Mn2+
iron(II) Fe2+
cobalt(II) Co2+
nickel Ni2+
copper(II) Cu2+
zinc Zn2+
Know the following substances –you will encounter them quite often:
FormulaName
HC Hydrochloric acid (called hydrogen chloride in gaseous form)
H2SO4 Sulphuric acid (hydrogen sulphate)
H2SO3 Sulphurous acid (hydrogen sulphite)
HNO3 Nitric acid
H2CO3 Carbonic acid (hydrogen carbonate, soda water)
NaOHSodium hydroxide (caustic soda)
Na2CO3 Sodium carbonate (soda ash or washing soda)
CaCO3 Calcium carbonate (marble or limestone)
NH3 Ammonia
NaC Table salt
The following prefixes indicate the number of atoms attached to the central atom:
Mono-indicates one, e.g. carbon monoxide – one oxygen (CO)
Di-indicates two, e.g. carbon dioxide – two oxygen atoms (CO2)
(Do not confuse ‘di’ with ‘bi’. ‘Bi’ is often used to indicate hydrogen, e.g. bicarbonate is –HCO3)
Tri-indicates three, e.g. sulphur trioxide – three oxygen atoms (SO3)
Tetra-indicates four, e.g. carbon tetrachloride – four chlorine atoms (CC 4)
The valency of an element is an indication of the number of electrons involved in a chemical bond. The valency of an element is usually determined by its position in the Periodic Table:
The valency of an element in group I is usually 1, in group II it is 2, in group III it is 3, in group IV it is 4, in group V it is 3, in group VI it is 2, in group VII it is 1 and in group VIII it is 0.
The valency of thetransition elements varies, butisusually 2, except silver, which is always 1.
If the valency deviates from these rules, the valency is usually indicated in brackets (Stock notation) e.g. iron(III)oxide, where the valency of the iron is 3; copper(I)chloride–valency of copper is 1, etc.
The valency of an ion is the same as the charge of the ion:
Ions with a valency of 1: NO3-,OH-,CH3COO-, MnO4-, Na+,NH4+, etc.(Charge is +1 or –1)
Ions with a valency of 2: SO42-,CO32-,Cu2+,Mg2+, etc.(Charge is +2 or –2)
Ions with a valency of 3: PO43-,N3-,Cr3+, etc.(Charge is +3 or –3)
The formula of a compound can be determined as follows:
Write down the two elements or ions, of which the molecule consists, e.g. A O
Write down their valencies above each. 32 A O
Simplify the ratio of the valencies if possible, e.g. 4 and 2 become 2 and 1.
Take the numbers in the direction indicated by the arrows:
The formula then becomes A 2O3
Another example: 2 1
The formula of copper(II) nitrate: Cu NO3 becomes Cu(NO3)2
Exercise 3:
1Give ONE word/term for
1.1an ion carrying a negative charge. (1)
1.2Na2SO3 (1)
1.3the household (general) name of sodium chloride. (1) 1.4SO42- (1)
1.5the formula for the carbonate ion. (1) 1.6CO32- (1)
Elements K, Ca, S and Br appear in the Periodic Table in the groups as shown here. Which formula is correct for a compound formed between two ofthese elements? 2 32 A O
ACaBr BKBr2 CCa2SDK2S (2)
3The formula of a compound of element X with atomic number 9 and element Y with atomic number 20 is AYX BY2X3 CY2XDYX2 (2)
IAIIAVIAVIIA KCaSBr
4A most likely formula for the compound formed from arsenic and oxygen is AAsO2 B As2OCAs3O2 DAs2O3 (2)
5A compound consists of the ions A3+ and B2-. A possible formula for the compound is
AA3B2 BA2B3 C(AB)6 D2A3B (2)
6The correct formula for aluminium oxide is:
AA 2O2 BA 2OCA 2O3 DA 3O2 (2)
7The correct name for CuC 2 is:
ACopper(I) chloride BCopper(II) chloride
CCopper(III) chloride DCopper chloride (2)
8The correctformula for aluminium hydroxide is:
AA 3(OH)2 BA 3(OH) CA 2(OH)3 DA (OH)3 (2)
9The correct formula for the phosphate ion is:
APO34- BPO43- CPO33- DPO44- (2)
10The common name of NH3 is:
ANitro BAmmoniumCHydromoniaDAmmonia (2)
11Work out the name and formula of the substance formed when the following elements bond:
11.1Na and S11.2Mg and N2 11.3Ca and O2 11.4P and O2 (8)
12Name the following substances:
12.1CaSO4 12.2CaCO3 12.3ZnSO4 12.4LiOH 12.5Mg(NO3)2 12.6SO2 12.7K2O12.8Mg(OH)2 (8)
13Writethe chemical formulae of the following:
13.1Beryllium oxide
13.2Hydrogen oxide
13.3Phosphorous pentoxide 13.4Calcium iodide
13.5Potassium sulphate 13.6Lithium carbonate
13.7Sodium nitrate 13.8Calcium hydroxide
13.9Sodium chloride 13.10Copper(II)sulphate (10)
14Write down the chemical formula for:
14.1Sodium carbonate 14.2Potassium nitrate
14.3Ammonium sulphate (6)
Matter and Classification: Metals, Metalloids and Non-Metals
Matter can be classified as metals, metalloids (semi-metals)or non-metals by using their properties.
Metalsand non-metals:
Most, but not all, metals and non-metals have the following properties:
Metals
Non-metals
Solids at room temperature (except mercury (Hg) Solids, liquids and gases at room temperature
Malleable, i.e. it can be beaten into different shapesBrittle –they are not malleable or ductile
Ductile, i.e. it can be drawn out into thin wires
Conductors of electricity Poor conductors of electricity –good insulators, exceptcarbon, in the form of graphite, which conducts electricity very well
Heat conductors Poor thermal (heat) conductors
Sonorous, i.e. rings when struck
New surfaces have a lustre, i.e. shiny
Hard
Strong
Metalloids are elements that have properties of both metals and non-metals, but mainly non-metallic.
Thefollowing can be considered as metalloids: Boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), polonium(Po)and astatine (At).
All elements in the lightly shaded area on the Periodic Table provided in the back of the bookare nonmetals, those in the non-shaded areaare metals and those in the darkly shaded area aremetalloids.
Matter and Classification: Electrical Conductors, Semiconductors and Insulators
Another way of classifyingmatter is as electrically conducting, semi-conducting or insulating
All metals are conductors of electricity.
Their conductivity decreases with increasing temperature
Metals that are good conductors of electricity can be used as conducting wires
Silver is the best conductor, but too expensive to use in transmission lines. Copper is almost as good as silver, hence copper is used instead. Although aluminium has a slightly higher resistance, its density is much less than that of copper and thereforetransmission lines are often made of aluminium.
Metals that conduct electricity, but havea high resistance, e.g. tungstenor nichrome (alloy of nickel, iron and chromium),can be used as heating elements in electric kettles, irons, heaters, etc.
All non-metals are not conductors of electricity and can be used as insulators (except graphite).
Some of the metalloids, such as silicon and germanium, are semi-conductors
Their conductivity increases with increasing temperature, the reverse of metals.
They can be used in diodes in computers and other electronic equipment.
Exercise 4:
1Give ONE word/term for
1.1elements that have properties of both metals and non-metals. (1)
1.2the electrical conductivity of the metalloids ….. with decrease in temperature. (1)
1.3the property of metals illustrated by stretching them to form wire. (1)
1.4the group ofelements to which boron belongs. (1)
1.5an example of a substancethat is malleable and ductile. (1)
1.6an example of a semi-conductor. (1)
1.7the type of elements that are malleable and ductile. (1)
1.8an element in Period 3that has greatly influenced the electronic industry. (1)
2Which ONE of the following regarding thermaland electrical conductivity in metals is TRUE?(2)
Thermal
3A hat will not be made of copper because
Acopper conducts electricity. Bcopper is malleable. Ccopper conducts heat. Dcopper is a pure compound. (2)
4Which ONE of the following elements will be the best conductor of electricity?
ASi BK CC DH (2)
5Classify the following elements as insulator, conductor or semi-conductor:
5.1Aluminium 5.2Arsenic 5.3Zinc5.4Lithium
5.5Silicon 5.6Oxygen 5.7Sulphur (7)
6A learner wants to determine which of a wooden ruler, a strip of aluminium foil or a polystyrene strip will conduct electricity. The learner is supplied with the following apparatus:
Two 1,5 V cells, a light bulb, conducting wires andcrocodile clips.
Write an experimental plan that the learner can follow to conduct this investigation. Include the following steps in the experimental plan:
Investigative question
Hypothesis
Method –steps that the learner can follow to perform the investigation Circuitdiagram –include a circuit diagram to support the method
Results –include a table that the learner can use to record the results
Conclusion –how to use/interpret the results to draw a conclusion (16)
7Write down THREE properties of metals.
8.1Is diamond a metal, a semi-metal or a non-metal?
8.2The properties of gold differ from that of diamond.
List TWO physical properties of gold that are not properties of diamond. (2)
9A learner collects materials listed in the table in order to investigate some of their physical properties.
Three of the observations made during the investigation are shown (as YES or NO) in the table, whilst others are represented by the letters (a) to (f).
Matter and Classification: Thermal Conductors and Insulators
Matter can be classified as thermally conducting or insulating In general metals are good conductors of heat. Silver is best, followed by copper, aluminium, steel. If different pieces of metal, e.g. spoons, are placed in the same beaker of hot water, you can feel the other end of the silver spoon getting hot faster than the stainlesssteel spoon. Non-metals are poor heat conductors and thus good insulators, e.g. asbestos, wood, cork, down, air. Soft clothing and bedding, a wet-suit, etc. have air (poor conductor)trapped in the material, hence loss of energy takes place slowly.
Exercise 5:
1Give ONE word/term for
9.1To investigate the conductivity of the materials, the learner connects the materials alternately in a closed circuit containing a battery and a light bulb. For this investigation, write down:
9.1.1The independent variable
9.1.2The dependent variable
9.1.3An investigative question
9.2Briefly describe how you will test whether the above materials are:
9.2.1Shiny or not
9.2.2Ductile or not
Sample
9.3Write down the observations, represented by the letters (a) to (f) in the above table thatthe learner should make. Copy the letter (a) to (f) into your answer book. Next toeach letter, only write down YES or NO. (6)
9.4Give TWO reasons why lightning conductors are made of copper. (2)
9.5State TWO other physical properties of magnesium not investigated in this investigation.(2)
1.1an example of a good thermal insulator. (1)
1.2an example of a good thermal conductor. (1)
1.3a material that does not allow the transfer of electricity or heat. (1)
2If it is cold, we get goose bumps, which push up the hair, trapping air between skin and hair. How does this help in cold weather? (2)
3Why do you think do buildings have a cavity wall trapping air and ceilings have insulation material trappingair? (2)
4Why do you think petanimals moult at the end of winter? What was the function of the fur they are now losing? (2)
5What sort of substance do you think is put into the wall of a fridge?Why? (2)
6Why is itbetter to use a wooden spoon to stir a pot on the stove, than one made from metal?(3)
7Matsoai wants to go camping and is looking for a suitable insulator to put underneath her mattress in hertent. She’s got a choice of three substances: NEWSPAPER, PLASTIC and TOWELS.
In order to assist her in her decision, she uses a sample of each material and conducts an experiment to test the insulating properties of each material. She uses the apparatus illustrated in the diagram and measures the decrease in temperature of the water over a fixed period of time for each of the three materials as insulator respectively.
Water Smaller container Material tested Larger container
7.1Explain the difference between a thermal conductor and an insulator. (2)
7.2Write down an investigative question for this investigation. (2)
7.3Write down a possible hypothesis for this investigation. (2)
7.4Name any TWO other apparatus needed to conduct this experiment. (2)
7.5Write down the independent variable for this investigation. (1)
7.6Write down the dependent variable for this investigation. (1)
7.7Write down ONE variable that has to be kept constant during this investigation (controlled).(1)
Matter and Classification: Magnetism
Matter can be classified as magnetic or non-magnetic
All substances can be magnetised, but some far moreand easierthan others. Only iron and a few other materials such as cobalt and nickel are attracted by a magnet. They are called ferromagnetic materials.
If a substance, e.g. iron, is magnetised and itretains its magnetism, it is classified as hard iron, if it loses its magnetism easily, it is called soft iron.
The ability to retain magnetism is called its retentivity –hard substances have a high retentivity. Hard substances areused to make permanent magnets and soft substances for electromagnets. Susceptability is the ease with which a material is magnetised.
It is usually difficult to magnetise a hard substance(we say it has low susceptibility) but once made, it retains itsmagnetism(we say it has high retentivity).
A soft magnet on the other hand has a high susceptibility and a low retentivity, i.e. it is easily magnetised, but loses its magnetism very easily.
Examples of magnetic substances:
Three metals in the Periodic Table that are magnetic areiron, cobalt and nickel.
Alnico is an alloy consisting mainly of aluminium, nickel and cobalt.Itis a very strong magnet. They have a wide variety of applications includingspeakers,motors, telephones, radars, relay switches, compasses, etc.
Ceramic magnets consist of two metals, one usually being iron, chemically combined with oxygen. They are cheaper to produce than Alnico magnets. They are used inspeakers, dc motors, etc.
Fridge magnets consist of a magnetic material mixed with a polymer.
Exercise 6:
1Give ONE word/term for
1.1material that can be attracted by a magnet. (1)
2Which ONEof the following is correct? Soft iron has
Aa low susceptibility and a high retentivity.Ba low susceptibility and a low retentivity.
Ca high susceptibility and a high retentivity.Da high susceptibility and a low retentivity. (2)
3Four classes of materials are given below:
metals ceramics glass plastics
Choose from the above list the class to which each of the following materials belongs:
3.1A is flexible, easily melted, can be moulded and does not conduct electricity. (2)
3.2B is strong, hard, can be bent and is a good conductorof both heat and electricity. (2)
3.3C is hard, transparent, strong when compressed, but weak when stretched. It is brittle.(2)
4Completethe following table giving examples of different materials and some of theirproperties: ExamplePossible use
5Consider the list of substances. The phase of each substance is written between brackets. Na(s) Air(g) Cu(s) O2(g)
Sb(s) Si(s) S(s) CuSO4(s)
Choose from this list:
(Only write down the number of the question and the substance or substances you choose next to it.) (Asubstance may be used more than once when answering the questions.)
5.1An element that is a non-metal. (1)
6Study the list of substances given below. Plastic H2SO4 Air Ge Sulphur Cu Fe B H2O( )
Choose from this list a substance that is:
(Only write down the substanceyou choose from the list next to the question number.) (A substance in the list can be used more than once.)
6.1An insulator 6.2A homogeneous mixture6.3Magnetic
6.4An intrinsic semi-conductor6.5Sulphuric acid 6.6A thermal conductor
Sample
5.2A substance that is a compound. (1)
5.3An element that is a good conductor of electricity. (1)
5.4Two elements that are semi-metals. (2)
5.5A substance that is a homogeneous mixture. (1)
5.6An element that is a semi-conductor. (1)
5.7Two substances that are metals.
5.8A molecule that is an element.
5.9A substance that is a good thermal insulator. (1)
6.7Asemi-metal 6.8An electrical conductor6.9A non-metal
6.10A pure substance (10)
The Kinetic Theory of Matter
The Kinetic Molecular Theory provides a model for the three phases of matter –solids, liquids and gases. Matter consists of small particles that are in constant motion
In solids the particles are packed closely together in a regular pattern and vibrate about a fixed point. In liquids the particles are arranged randomlyand also close togetherand they can move past one another.
In gases the particles are arranged randomly and far apart. They move very fast and collide with one another and the sides of the container, exerting pressure.
The particles have potential energy due to the forces of repulsion and attraction between them. It is important to notice that when a substance changes phase, the forces between the particles change (it is different for solids, liquids and gases) and hence the potential energy changes
The particles have kinetic energy due to their motion
The temperature of a substance is directly proportional to the average kinetic energy of the particles. It is important to notice that while the temperature increases, the average kinetic energy of the particles also increases and constant temperature implies constant average kinetic energy.
As the temperature of a solid increases, the particles move faster. The particles’ energy of motion (kinetic energy) overcomes the forces of attraction between the particles and the solid melts.
If the temperature is further increased, the kinetic energy further increases, weakening the forces of attraction and the liquid evaporates.
Exercise 7:
1Give ONE word/term for
1.1the measure for the average kinetic energy of the particles of a substance. (1)
1.2thephysical quantity that is a measurement of the average kinetic energy of a substance.(1)
2The volume of a fixed mass of gas is reduced without a change in the temperature.
The gas pressure increases because
Athegas particles are now moving faster.
Bthe gas particles have increased in number.
Cthere is a greater distance separating the gas particles.
Da greater number of collisions per unit time now occurs against the container walls.(2)
3The liquefaction of gases is evidence of the fact that
Amolecules are moving.
Bmolecules occupy volume.
Cthere exist forces between molecules.
Dmolecules have open spaces between them. (2)
4Temperature is a measurement of the … of the particles of a substance.
Apotential energy Baverage kinetic energy
Cinternal energy Dkinetic energy (2)
5On aerosol cans there is a warning not to leave them in strong sunlight or to throw them onto a fire. In terms of the kinetic theory explain why this warning is necessary. (2)
States of Matter and the Kinetic Molecular Theory
Physical state is another way of classifying materials.
There are three physical states of matter – solid, liquid and gas
Intermolecular forces determine the state of a substance –if the forces are very strong, it is a solid, if the forces are not so strong, it is a liquid and if the forces are weak, it is a gasat room temperature.
Kinetic Molecular Theory:All substances are made up of small particles that are in constant motion. This can be verified by Brownian motion and diffusion.
Brownian motion:Tiny suspended particles, e.g. smoke in air or pollen on motionless water, studied through a microscope, are constantly ‘pushed’ around by the moving air or water particles.
Diffusion is the spontaneous movement of asubstance from a region of higher to a region of lower concentration, e.g.: If a drop of food colouringor a potassium permanganate crystalis carefully placed in a glass of water, the coloureventually spreadsuniformlybecause of the random movement of the molecules. The odour of perfume spreadingis another example.
The diagrams illustratethe arrangement of particles for the three states of matter:
In a solid:
The particles are closely packed in an orderly pattern with little space between the particles.
The particles vibrate about a fixed position.
A solid maintains a fixed shape and size.
It is not readily compressible.
The forces of attraction between the particles arevery strong. In a liquid:
The particles are also rather closely packed withlittle space between the particles. The particles move around freely and the liquid takes on the shapeof the container.
Like a solid, it is not readily compressible.
The forces of attraction between the particles arefairly strong, but weaker than in solids. In a gas:
The particles are very far apart and they move about freely to fill the whole container. It is easily compressed.
The forces of attractionbetween the particles arevery weak.
Property Solid Liquid Gas
Spacing of particlesVery little space between particles Space between particles slightly more than solid Distance between particles very large
Movement of particlesVibrate about fixed position Free to move about in liquid due to spaces Free to move
Arrangement of particlesOrderly –fixed patternDisorderly Disorderly
Forces between particlesVery strong Not so strong Very weak
Shape Fixed shape and size Fixed volume, but takes onshape of container Takes on volume and shape of container
Compressibility Not compressibleNot readily compressibleCompressible
Melting is the change from solid to liquid.
Freezing is the change from liquid to solid.
Evaporation is the change from liquid to gas.
Condensation is the change from gas to liquid.
Sublimation is the direct change from solid to gas.
from solid to liquid (melting) or from liquid into gas (boiling). We learn in a later chapter about these forces, but for now it will suffice to know that the greater the molecules, the greater the force and the higher the melting and boiling points
If the temperature of a substance is above its boiling point, the substance will be a gas
If the temperature of the substance is between boiling and melting point, the substance isa liquid
If the temperatureof the substanceis below the melting point,the substance will be a solid
A heating curve for water is obtained by starting with a thermometer in a beaker of ice that is heated. The temperature is determined every 10 seconds, whilst stirring with the thermometer.
Heating curve of water
Cooling curve of water
Boiling point
The freezing point of a substanceis the constant temperature while a liquid changes into a solid.
The melting point of a substance is the constant temperature while the solid changes into a liquid.
The boiling point of a substance is the constant temperature while the liquid changes into gas.
Evaporation takes place at the surface at all temperatures, but at the boiling point evaporation takes place throughout the liquid.
The melting and boiling points of a substance aredetermined by the forces keeping the molecules together. If these forces are strong, a lot of energy is required to separate the molecules to change
Sample
Boiling point Water starts boiling
Melting point
All the water has changed into steam
Ice starts melting
Melting complete
Melting point
Freezing starts
Freezing complete
A cooling curve is obtained by starting with a thermometer in a beaker of boiling water. The temperature is determined every 10 seconds, whilst stirring with the thermometer. Note that in both the heating and cooling curve of water the temperatureof the waterremains constant while the water is changing state.The reason is that while it is changing state, all the energy is involved in changing the arrangement of the particles and no energy is used to change the kinetic energy of the particles, hence no change in the temperature.
A very important aspect to understand at this point is:
While ice is melting (solid to liquid) the temperature of the water remains constant, but it absorbs heat from the surroundings –in the absence of a flame, the container will become cold.
This also explains why it is so cold whensnow is melting.
While water is boiling (liquid to gas) the temperature of the water remains constant, but it absorbs heat from the surroundings, e.g. a flame. If however evaporation takes place at normal temperatures, water absorbs heat from its surroundings and the container will become cold E.g. during perspiration it evaporates, cooling you down; a wet clay pot or wine cooler keeps the contents cool, because the water in the clay evaporates;a wet cloth is cooler than a dry one, etc.
While steam condensates (steam to liquid) the temperature of the water remains constant, but it releases heat to its surroundings. This explains why steam at 100 ºC causes more damage than boiling water at 100 ºC. If however condensation takes place at normal temperatures, the water releases heat to its surroundings, e.g. during cloud formation in the air.
While water freezes (liquid to solid) the water releases heat to its surroundings.
Summarized: While it melts or boils,it absorbs energy
The temperature (i.e. kinetic energy)of the substance remains constant, but the potential energy (to move the particles further apart) increases
While it freezes or condenses, it releases energy. The temperature (kinetic energy)of the substance remains constant, but potential energy (when the particles move closer) increases
In between, when thetemperature changes, the kinetic energy changes and the potential energy remains almost the same.
Exercise 8:
1Give ONE word/term for
1.1the temperature at which a liquid changes into a solid. (1)
1.2theprocess during which a liquid changes into a gas. (1) 1.3the spontaneous movement of a substance from a region of higher to a region of lower concentration. (1)
1.4the direct change from solid to gas. (1)
1.5thetheory that states that all substances are made up of small particles that are in constant motion. (1)
1.6the change from solid to liquid. (1)
2Study the following list of melting and boiling points and answer thequestions thatfollow:
NameFormulaMelting pointBoiling point
OxygenO2 –219ºC–183 ºC
NitrogenN2 –210ºC–196 ºC
EthanolC2H5OH–114ºC78ºC
Ammonia NH3 –78ºC–33 ºC
LeadPb327ºC1750ºC
MethaneCH4 –183ºC–162ºC
ButaneC4H10 –138ºC0ºC
OctaneC8H18 –57ºC126ºC
HexadecaneC16H34 19ºC288ºC
EicosaneC20H42 37ºC344ºC
2.1Which of the substances are gases at room temperature(25 ºC)? (5)
2.2Which of the substances are liquids at room temperature? (3)
2.3Which of the substances are solids at room temperature? (2)
2.4What tendency do you notice in the melting and boiling points of methane to eicosane?(2)
2.5C25H52 is one of the main ingredientsin the candles we buy but C20H42 is not. Explain why not. (5)
2.6You need to separate oxygen and nitrogen. One possible method is by selecting a temperature at which one of the two substances is a gas and one is a liquid. Suggest a suitable temperature.(2)
3Explain why a motor car engine will never overheat while it has water circulating in its cooling system. (3)
4Water is an exceptional liquid in many ways and makeslife on earth possible. The heating curve for water is illustrated.
4.1Which letter on the graph represents water in the liquid phase? (2)
4.2Write down the phase change represented by the letter D. (2)
4.3The temperature does not increase during the phase change mentioned in the previous question.
Write down a reason for this observation. (2)
4.4We normally experience cold weather when the snow on the mountains starts melting.
Give a reason for thisphenomenon. (2)
5During strenuous exercise athletes sweat. In this process, a breeze helps their bodies to cool down.
7A learner returns home from school on a hot afternoon. In order to get cold water to drink, she puts ice cubes into a glass of water. She makes the following observations:
Observation I:The ice cubes float in the water.
Observation II:After a while the water becomes cold and the ice cubes melt.
7.1What property of ice cubes allows them to float in the water? (1)
7.2Briefly explain why the water gets cold as the ice cubes melt. (4)
7.3Briefly describe how the property mentioned in question 7.1 affects the sustainability of aquatic life during winter. (2)
8The kinetic theory is a study of the microscopic behaviour of matter to enable us to explain the macroscopic properties of matter.
Sample
The following are some of the assumptions of the kinetic theory:
All matter consists of small particles that are in constant motion.
Particles can move closer or further apart from each other. There are forces of attraction between particles.
8.1Write down the macroscopic property of matter that is related to the average kinetic energy of molecules. (1)
8.2Refer to the assumptions listed above to explain the difference between the solid phase and the gaseous phase of matter. (3)
8.3Referto the kinetic theory of matter to explain why there needs to be gaps between railway bars.(3)
9Boiling point is a physical property of substances.
9.1State ONE factor that determines the boiling point of substancesat constant pressure. (1)
9.2Which one of octane (C8H18) or wax (C23H48) will have the higher boiling point?
Explain your answer. (4)
The Atom: Basic Building Block of all Matter
Everything in the world is made up of different combinations of atoms from the elements on the Periodic Table.
The Periodic Table displays the elements in increasing atomic number.
5.1Explain how the breeze helps their bodies to cool down when they sweat. (2)
5.2Copy the diagram in your book. During the cooling process the molecules undergo a phase change. Use circles (O) to represent the molecules in each phase. Indicate the name of the phase change above the arrow. (4)
5.3Name the type of energy involved in the phase change. (2)
6.1Define the term boiling point (2)
6.2Is boiling a physical or chemical change? Give a reason for your answer. (2)
The Periodic Tableshows how periodicity of the physical and chemical properties of the elements relatesto atomic structure.
Please note that the list of key discoveries re the atom is not for exam purposes.
The atomic radius (size of atom) decreases from left to right on the Periodic Table (because the larger charge on the nucleus exerts a stronger force on the outerelectrons) and increases from top to bottom (because the number of energy shells increases).
The size of the nucleus relative to thatof the atom is like amarble lying on a rugby field, i.e. the atom is mainly an empty space with the nucleus occupying a very smallspacein any atom.
The atomic mass generally increases as the atomic number increases.
The mass of the hydrogen atom is approximately 1,7 x 10-27 kg –most of this mass is concentrated in the small nucleus. (Masses and diameters will be providedif needed.)
Relative atomic mass Ar, is a number, without units, indicating how many times the mass of the atom is larger than 1/12 of the mass of a C-12atom.
Rutherford’s alpha–particle scattering experiment confirms the above properties of the atom: -particles(an alpha-particle is a helium nucleus consisting of two protons and two neutrons)was directed at a thin gold foil. A fluorescentscreen was used to detect particles passing through.
What he observed was that most of the particles passed throughundisturbedas expected, but the surprising observation was that some were slightly deflected, whilstafew others were reflected.
The conclusion was that most of the particles passed through because the atoms are mostly empty space, with almost all the mass concentrated in the very small positive nucleus –the negative electrons in the empty space hardlyhave any mass.
Those positive particles that passed close to the positive nucleus wererepelled, i.e. they wereslightly deflected, but those few colliding head-on with a nucleus, were deflected backwards.
Fluorescent screen
Undeflected -particles
Reflected -particles
Structure of the Atom: Protons, Neutrons, Electrons
1Give ONE word/term for
An atom consists of:
Protons in the nucleus. Each proton has a charge of +1 and a mass of 1 u.
(1 u is the mass of 1/12 of the C-12 atom.)
Deflected -particles
Gold foil
Source of narrow beam of fast- -particles
Exercise 9:
1.1the mass of an atom on a scale where carbon-12 has a mass of 12. (1)
2If a beam of alpha-particles is directed at thin gold foil, most of the particles pass through without change in direction. A small percentage, however, is scattered through large angles. From this it can be deduced that
Aalpha-particles are not charged.
Bgold nuclei are surrounded by electrons. Cgold has a high density.
Dthe greatest part of the mass of an atom is concentrated in the positive nucleus. (2)
3If Rutherford used neutrons instead of alpha particles in his scattering experiment, the neutrons would …
Anot deflect because it has no charge.Bhave deflected more often. Chave been attracted to the nucleus easily.Dhave given the same results.(2)
4An alpha-particle is a helium nucleus consisting of two protons and two neutrons.
4.1What is the relative massof an alpha-particle? (3)
4.2The fact that most of the particles went through the thin foil leads us to what conclusion?(2)
4.3The fact that one of the alpha particles was reflected, leads us to what conclusion? (1)
5One atom of carbon has a mass close to 2 x 10-23 g. How many atoms would there be in 12g of carbon? (3)
6Why do values of relative atomic and relative molecular mass have no units? (2)
7During his studies of the atomic theory, Rutherford bombarded a gold foil with alpha particles.
The results obtained are illustrated in the diagram. The arrows represent the paths taken by the alpha particles.
7.1Write down the notation for an alpha particle.(3)
Gold foil enlarged showing gold atoms allowing -particles to pass through, deflecting one slightly and reflecting one backwards. e A Z n X
7.2Describe the THREE observations that Rutherford made.(3)
7.3State THREE conclusions regarding the structure of an atom that Rutherford made from this experiment. (3)
Source of alpha particles
Neutrons in the nucleus. Each neutron has no charge and it has a mass of 1 u.
Electrons moving in different energy levels around the nucleus. Each electron has a charge of –1 and a negligible mass.
The atomic number (Z) is the number of protons in the nucleus of the atom –this is given on the Periodic Table.
The mass number (A) is the number of nucleons (protons + neutrons) in the nucleus. In a neutral atom the number of electrons is the same as the atomic number(number of protons). When a neutral atom loses one or moreelectrons, a positiveion (cation)is produced with a charge equal to the number of electrons lost.
When a neutral atom gains one or moreelectrons, a negativeion (anion)is produced with a charge equal to the number of electrons gained.
An atom (nuclide)X can be represented by where X represents the element, A the mass number and Z the atomic number.
The number of neutrons is A –Z.
1Give ONE word/term for
Exercise 10:
1.1protons and neutrons in the nucleus of an atom. (1)
1.2the number of nucleons in the atom. (1)
2The nucleus of contains
A23 protons and 11 neutrons. B23 protons and 11 electrons. C11 protons and 12 neutrons. D11 protons and 12 electrons. (2)
3An approximate value for the relative atomic mass of an element may be obtained by
Acounting the number of electrons in one atom of the element.
Bcounting the number of protons in one atom of the element.
Ccounting the number of neutrons in one atom of the element.
Dadding together the number of protons and neutrons in one atom of the element. (2)
4How many protons, neutrons and electrons are there in an A 3+ ion of an atom? (2)
ProtonsNeutronsElectrons
A1314 11 B1314 10
C1013 27 D1427 13
5Which of the following is not true for (2)
AThe atom has a mass number of 14.
BThe atom is an isotope of .
CThe nucleus contains 8 protons.
DThere is a total of 14 protons and neutrons in the nucleus.
6Write down the number of protons, the number of neutrons and the number of electrons in (6)
7Potassium ion, sulphur atom, fluoride ion, bromine atom, carbonate ion.
From the above, name the one
7.1with only 16 protons; (2)
7.2that contains more than one element; (2)
Gold foil
7.3whichhas the same electron configuration as an atom of neon; (2)
7.4with the smallest mass. (2)
Structure of the Atom: Isotopes
Isotopes areatoms of the same element (same atomic number Z) but havingdifferent numbers of neutrons (different mass number A).
The majority of elements are found in nature as a mixture of isotopes.
The relative atomic mass Ar(X) of an element iscalculated by using the percentage of each isotope in asample of the naturally occurringelement and the relative atomic mass of each of the isotopes.
This is the number that is given on the Periodic Table.
Write down the number of the question on your answer sheet with the answer next to it.(9)
8Calculate the relative molecular masses of the following substances: (10)
Example:A sample of chlorine contains 75% of the isotope and 25% of the isotope. This means that 75out ofevery 100 chlorine atoms will have a relative mass of 35 and 25atomswill have a relative mass of 37.
The average mass ofchlorine atomswill thus be(75/100)(35) + (25/100)(37) = 35,5
The relative mass provided on the Periodic Table gives the average relative mass of its isotopes. The fact that it is not a whole number does not mean that it contains a fraction of a proton or neutron, but merely that it is the average of the isotopes
The relative formula mass, Mr(X), of a compound is obtained by adding the relative mass numbers of the atoms composing the molecule and it has no units.
Exercise 11:
1Give ONE word/term for
1.1atoms of the same element with different numbers of neutrons. (1)
2Two particles, X and Y,have the following composition:
X:16 protons, 16 neutrons, 18 electrons Y:17 protons, 20 neutrons, 18 electrons X and Y are
Aisotopes. Batoms of alkali metals. Cnegative ions. Datoms of metals. (2)
3Which ONE of the following pairs of elements contains the same number of neutrons?
and B and C and D and
4Which ONE of the following pairs represents two atoms with the same number of neutrons?
and B and
5Define the term isotopes
and D and
6An element X consists of the following five types of atoms:
6.1What are the five types of atoms of X called?
6.2Concerning the composition of atoms of X, in what 6.2.1 two ways do they correspond?
6.2.2
Sample
9The three isotopes of hydrogen haverelative masses of 1,0078, 2,0141 and 3,0161. Their respective % abundances are 99,985%, 0,015% and 0%.
Calculate the relative atomic mass of hydrogen, correct to the third decimal place. (3)
10The three isotopes of magnesiumhave relative masses of 24, 25 and 26. Their respective % abundances are 79%, 10% and 11%.
Calculate the relative atomic mass of magnesiumcorrect to the second decimal place. (3)
11Two carbon atoms X and Y are shown here:
11.1They are called …….. of the same element. (1)
11.2Which has the largest atomic number? (1)
11.3How many neutrons does X have? (2)
12Complete the table: (30)
NameSymbolMass number Atomic number Number of protons
7One of theisotopes of sodium is . Complete the following table with reference to the isotope.
and
13Uranium exists as two isotopic forms: uranium-235 ( ) and uranium-238 ( ). Enriched uranium-235, which is highly reactive, is used in the generation of electricity and in nuclear weapons. When a country acquires enriched uranium-235, their neighbouringcountries become nervous and suspicious.
Uranium-235 forms about 0,7% of the total uranium content of the earth.
Stable uranium-238, which is not suitable for use in nuclear reactors, makes up 99,3%.
13.1Define the term ‘isotope’. (2)
13.2Calculate the relative atomic mass of uraniumcorrect to the second decimal place. (4)
13.3Explain why uranium-238, although more abundant, is not suitable for use as fuel in nuclear reactors. (2)
13.4Name ONE benefit and ONE disadvantage of uranium-235 to humanity. (4)
18
and 8 X2-
14Study the following notation that represents an unknown ion and then answer the questions that follow.
14.1Write down the number of protons X has. (1)
14.2Calculate:
14.2.1The number of neutrons X has. (1)
14.2.2The number of electrons Xhas. (1)
14.3Write down the:
14.3.1 Atomic number of X. 14.3.2 Mass number of X. (2)
14.4Identify X. (3)
14.5Provide an explanation for your answer in question 14.4. (3)
Read the following paragraph and then answer the questions that follow.
ATOMIC MASS
Something that puzzled scientists in the past considerably was the fact that the relative atomic masses of elements are not integral multiples of that of carbon. This fact can now be explained. The atoms of the elements are mixturesof isotopes of different masses and the values obtained were the average masses of the atoms as they occur in nature. The percentages in which the different isotopes of a given element occur are practically constant and hence the average values are reliable for most practical purposes.
14.6Provide a definition for ‘relativeatomic mass’ of an element. (2)
14.7Neon (Ne) has three isotopes. Use the information in the table below tocalculate the relative atomic mass of neon correct to the first decimal place. (4)
Isotope of neon Percentage occurrence in nature
20Ne 90,0%
21Ne 0,27%
22Ne 9,73%
15.1Define the term ‘isotope’.
Give a reason for the answer. (2)
17.4Copper occurs in the following atomic forms: :69,2% and : 30,8%
Use the above information to calculate the relative atomic mass of copper. (4)
Electron Configuration
Electrons are arranged in different energy levels around the nucleus. The first energy level(n = 1)is closest to the nucleus and haslowest energy. The second and higher energy level (n = 2) is further away from the nucleus, etc.(Similar tofloors in a building.)
Each energy level contains one or more orbitals.(Similar to each floor containingone or more flats.)
An orbital is the space in which an electron can probably be found.
Thefirst energy level contains a singleSorbital, which has a spherical shape and called the 1S orbital. The second energy level has one spherically-shaped S orbital (called 2S orbital) and three dumbbellshaped p orbitals –one along the X-axis, the other along the Y-axis and the other along the Z-axis (called 2px, 2py and 2pz).The S orbital in an energy level has a slightly lower energy thanthe p orbitals in the same energy level, but all the p orbitals in the same level havethe same energy.
15.2.1Its mass number
15.2 , also called tritium,is an isotope of hydrogen. Write down:
15.2.2Its atomic number (1)
15.2.3The number of electrons it has (1)
15.2.4The number of neutrons it has (2)
15.2.5The number of nucleons it has. (1)
15.3Deuterium is another isotope of hydrogen.
15.3.1Use the notation to write down this isotope. (2)
15.3.2. Compare deuterium to the isotope of hydrogen in 15.2. (4)
15.4The mass spectrogram of magnesiumshows that it has three isotopeswith the following compositions:
Magnesium 24 –80%
Magnesium 25 –10%
Magnesium 26 –10%
15.4.1Write down the atomic number of magnesium in each of these isotopes. (2)
15.4.2Calculate the relative atomic mass of magnesium. (5)
16Magnesium has three naturally occurring isotopes.
The magnesium isotopes Mg-25 and Mg-26 are used to study the absorption and metabolism of Mg in the human body and are also used to study heart disease. The relative abundances and masses of the threeisotopes of magnesium are given in the table.
Sample
16.1How many protons, electrons and neutrons does a neutral atom of Mg-25 have? (3)
16.2Write down the electron configuration, using the sp-notation, of the isotope Mg-26. (3)
16.3Using the information abovecalculate the relative atomic mass of magnesium. (4)
17Many elements occur in different atomic forms.
2 3 1 , als H n A Z to w X as 1 1 H 2 , 1 , an H d nd 3 1 H
Energyleveldiagram(AufbauPrinciple):
Energy level diagram (Aufbau Principle):
The Aufbau Principle states that the orbital that fills firstwith electrons is the orbital withlowest energy. In atoms the order for filling of orbitals is 1S, 2S, 2p, 3S, 3p, 4S, 3d, 4p, …..
Rules for occupation of orbitals:
The number of electrons can be determined from the atomic number –if the atom is neutral, the number of electrons will be the same as the atomic number, but if it is an ion, the atom has gained or lost electrons and thishas to be taken into consideration.
The orbitals are filled from the lowest level, i.e. 1S, 2S, 2p, 3S, etc.
Pauli’s Exclusion Principle:An orbital can accommodate a maximum of two electrons with opposite spin.
These two electrons with opposite spin, occupying the same orbital, are called an electron pair. Hund’s Rule: If more than one orbital with the same energy, e.g. 2px, 2py and 2pz, haveto be filled up, each of themwill receive only one electron before any one receives a second electron.
An electron can absorb energy and go to a higher energy level –it is then in an excited state
The spectroscopic electron configuration can be written as 1S2 2S2 2p6 3S2 3p6, etc., where the 1 in 1S2 indicates the main energy level in which the electron is, the S in 1S2 indicates the type of orbital it is occupying and the 2 in 1S2 indicates the number of electrons occupying that orbital.
Valence electrons are the electrons in the outermost energy level.
The arrangement of the electrons around the nucleus can also be indicated using the orbital box diagrams or Aufbau diagrams or arrow in a block diagrams
Each arrow represents an electron and the direction of the arrow indicates the directionof spin, which can either be up or down.
The following example shows the arrangementof 14 electrons.
Exercise 12:
For example, hydrogen occurs as , , and .
17.1Write down TWO similarities in atomic structure of the above three hydrogen atoms. (2)
17.2Write down TWO differences in atomic structure between the above three hydrogen atoms.(2)
17.3How do the chemical properties of these three hydrogen atoms compare?
1Give ONE word/term for
1.1the principle that the orbital that fills first is the orbital with the lowest energy. (1) 1.2the principle which states that an orbital can accommodate a maximum of two electrons.(1) 1.3the space around an atom's nucleus where the probability of finding an electron is the greatest. (1)
1.4the region (in space) where electrons will be found in an atom. (1)
2The particle which does not have the same electron distribution as the neon atom, is
AF- BBe2+ CO2- DA 3+ (2)
3The number of electrons which an orbital may contain is
Aequal to the atomic number of the element.
B2, 8 or 18 depending on the main energy level concerned.
C0, 1 or 2.
D2 only. (2)
4The valence electron configuration of element X is 3S2 and that of element Y is3S2 3p2
What is the empirical formula for a compound of X and Y?
BXY2 CX2YDX2Y3 (2)
5Which ONE of the following has the same electron configuration as a potassium ion?
ANa+ BMg2+ CA 3+ DC - (2)
6The ion 12X+ has the same electronic structure as the element
BNe CSi DF (2)
7How many valence electrons does helium have?
A0B1C2D3 (2)
8The natural valency of a nitrogen atom is 3 because
Anitrogenis in period 3 of the Periodic Table.
Bthe electron structure of nitrogen is 1S2 2S2 2p3
CHund’s rule for electron structure applies.
Dthe hybridisation theory may be applied to a nitrogen atom as it is applied to carbon.(2)
9Which ONE of thefollowing represents an atom in the excited state?
A1S2 2S2 2p1 B1S2 2S2 2p6 3S1
C1S2
10The total number of electrons needed to completely fill all the orbitals in an atom's second principal energy level
11Which ONE of the following electron configurations represents a sodium ion?
12.312.3.1In what respect does IV differ from II? 12.3.2What is IV of II? (4)
13The atomic numbers of elements X and Y are 12 and 18respectively. Write down the electron configuration of 13.1X; 13.2Y. (4)
14.1What is meant by the term atomic orbital? (3)
14.2What is the shape of 14.2.1an Sorbital? 14.2.2a p orbital? (4)
Sample12The electron configurations of four sodium particles are given below:
12.112.1.1Howdoes the energy content of I differ from that in II?
12.1.2What is I called of II?
12.2.2Whatare
14.3The electron configurationfor an atom with 11 electronsis: 1S2 2S2 2p6 4S1 Write down the ground state electronic configuration of this atom. (2)
15.1Write down the electron configuration of a magnesium atom. (2)
15.215.2.1Write down the electron configuration of a magnesium ion. (2)
15.2.2What is the symbol for this ion?
15.3What is the empiricalformula for the compound which forms betweenmagnesium and fluorine?(2)
16An atom of element A can be represented as .
Alongside is a diagrammatic representation of the electron structure of the ion of a certain isotope of A.
16.1Write down the name of element A. (2)
16.2How many neutrons are therein one atom of this isotope?(2)
16.3Draw a sketch which shows the shapes and relative sizes of the orbitalswhich contain the valence electrons of a neutral atom of A (in the ground state.)(6)
16.4Write down the formula and name of the compound which is formed when element A combines with hydrogen. (4)
17The electron structure of a hydrogen atommay be represented as follows: 1S1 Use this notation in answering questions 17.1, 17.2 and 17.3.
17.1Write down the electron structure of an ion of the aluminium-27 isotope in the ground state.(3)
17.2Write down the electron structure of a neutral atom (in the ground state) of any other isotope of aluminium. (3)
17.3Write down the electron structure of any neutral aluminium atom inthe excited state. (3)
18The carbon atom in the ground state has 2 unpaired electrons and for this reason might be expected to form, at most, 2 covalent bonds. Carbon is however tetravalent. Give the energy level diagram (arrows in a circle) for the carbon atom in an excited state.(2)
19An excited scandium atom with 44 nucleons has the following electron configuration: 1S2 2S2 2p6 3S2 3p6 4S2 5S1
19.119.1.1What is meant by the excited state of this atom? (2)
19.1.2Is the excited state a stable or unstable state? Explain your answer. (4)
19.2Write the electron configuration of 19.2.1this atom in the ground state. (3)
19.2.2a triple positively charged ion of this atom. (3)
19.3Write down a symbol of an isotopeof this scandium atom in the form where x and y are appropriate numbers. (3)
20Use the ‘arrows in circles’ (or ‘arrows in boxes’) notation with labels to represent theelectronic structure of . (5)
21Show the electron distribution of the following using Aufbau diagrams: 21.1Ar21.2Ca2+ 21.3C - 21.4Na
AXY3
A2 B8 C16 D32 (2)
22Write down the electron configuration of the Na+ ion using the S,p,d notation. (3)
23Silicon is one of the most abundant materials in the earth’s crust.
Silicon is also one of the materials that caused the revolution in the computer industry.
23.1Howmany valance electrons does asilicon atom have?
23.2What property of silicon makes it so useful in the electronic industry?
23.3Name TWO other household uses of silicon.
The Periodic Table
The Periodic Table displays the elements in increasing atomic number. The columns are called Groups
All the elements in the same group have the same valence electron structure
The chemical and physical properties of an element dependon its valence electron structure –hence all the electrons in the same group have the same chemical and physical properties
The first column is called Group 1 or I, the second column is Group 2 or II, etc.
All the elements in group 1 or Ihave just one valence electron and they are called the alkali metals
All the elements in group 2 or IIhave 2 valence electrons and they are called the alkali earth metals
All the elements in group 17 or VII have 7 valence electrons and they are calledthe halogens
(Please note that all the elements ending on –gen are diatomic, i.e. they do not exist as single atoms, but as moleculesconsisting of two atoms, e.g. hydrogen, nitrogen, oxygen and all the halogens.)
All the elements in Group 18 or VIII have 8 valence electrons and are called the noble gases
All elementsin the centre block (Groups 3 –12) are the transition elements
Each row is called a Period
The first row, or Period 1, contains the elements of which the valence electrons (outermost electrons) are in the 1st energy level(n = 1). The second row, or Period 2, contains all the elements of which the valence electrons are in the 2nd energy level(n = 2), etc.
The first energy level can accommodate a maximum of two electrons, hence there are two elements in period 1; the second energy level can accommodate a maximum of 8 electrons,hence there are 8 elements in Period 2, etc.
Therefore, if for example, an element is in row or Period 3, we know that it has 3 energy levels,andif it is in column or Group 2, it has 2 electrons in the outer energy level, with the inner levels filled.
Density generallyincreases in a period from left to right with highest density in Group IIIwhere afterit decreases.
From top to bottom in a period the density generally increases, but K is less dense than Na.
Melting point as well as the boiling point generally increasesfrom left to right in a period, with the highest boiling and melting point in Group 14,where afterthey gradually decrease.
From top to bottom in a group, the melting and boiling point generally decrease.
Atomic radius decreases from left to right in a period due to the stronger attraction by the larger positive nucleus on the negative electrons. It increases from top to bottom in a group due to the extra energy level that each new period attains.
Formulae of halides (halogen-containing compounds) of Period 2 are LiX, BeX2, BX3, CX4, NX3, OX2, XX, where X represents any halogen.
Formulae of oxides of Period 2 are Li2O, BeO, B2O3, CO2 and there are several forms of nitrogen oxide –the most abundant in the air are N2O, NO and NO2
Electronegativity is the tendency of an atom to attract the shared electrons in a bond.
The first ionisation energy increases from left to right (because of increasing charge on nucleus) resulting in the metals (left on Periodic Table) having the lowest ionisationenergies. Hence metals easily lose electrons, forming positive ionswhile non-metals (on the right, with high ionisationenergies) tend to gain electrons, forming negative ions.
The ionisationenergy decreases from top to bottom (because the inner electrons shield the valence electrons andthe valence electrons are alsofurther away from the nucleus).
The ionisationenergy to remove an electron from the inner electronsis very high.Hencealthough the elements in Group 1 have low first ionisationenergies,their secondionisationenergyis very high.
Similarities in Chemical Properties among Elements in a Group
Sample
Electronegativity increases from left to right in a period on the Periodic Tableand decreases from top to bottomin a group.
Electron-affinity (liking for electrons) is the amount of energy released when an atom in the gas phase gains an electron to form a negative ion.
Electronaffinityincreases from left to right on the Periodic Table anddecreases from top to bottom. First ionisation energy isthe amount of energy required to remove the first electron from an atom in the gaseousphase to produce a positive ion.
Similarly second ionisationenergy is energy required to remove the second electron, etc.
The elements in Group 1 or I, called the alkali metals, are hydrogen, lithium, sodium, potassium, rubidium, cesium, and francium. Hydrogen rarely behaves like the alkali metals.
All the elements in Group1 or I have a single electron in its outermost energylevel in its S orbital and hence we say that the elements of Group 1 lie in the S block.
They readily lose this electron, producing an ion with charge +1, e.g. H+,Li+,Na+,K+, etc.
The reactivity of the Group 1 metals increases from top to bottom.
All the alkali metals react aggressively with the halogens to form ionic salts.
They all react with water to form strong alkaline hydroxides –the heavier alkali metals react vigorously with water.
From the above information we can conclude what the chemical properties of any element in Group 1, which we are not familiar with, e.g. francium, will be –it will react very aggressively with the halogens to form ionic salts and extremely vigorously with water.
The elements in Group 2 or II, called the alkali earth metals, are beryllium, magnesium, calcium, strontium, barium, radium.
All the elements in Group 2 or II have 2 electrons in its outermost energy level in its S orbital and hence we say that the elements of group 2 lie in the S block.
They readily lose these two electrons, producing ions with charge +2, e.g. Be2+,Mg2+,Ca2+, etc.
The reactivity of the Group 2 metals increases from top to bottom.
All the alkali earth metals react aggressively with the halogens to form ionic salts.
They all react with water to form strong alkaline hydroxides –the heavier alkali earth metals react vigorously with water.
The elements in Group 17 or VII, called the halogens, are fluorine, chlorine, bromine, iodine,astatine. All the elements in Group17 or VII have seven electrons in its outermost energy level, with its S orbitals filled and 5 electrons in its p orbitals –hence we say that the elements of Group 17 lie in the p block.
They tend to gain one electron in order to completely fill the valance electron level, thus producing ions with a charge –1, e.g. F- , C - , Br- , I- , etc.
The reactivity of the halogens decreases from top to bottom.
The elements in Group 18 or VIII, called the noble gases, are helium, neon, argon, krypton, xenon and radon.
All the noble gases have eight electrons in its outermost energy level, with the S orbitals as well as the p orbitals filled.
They are all unreactive because they are stable –thistype of electron configuration, with the energy level completely filled, is a very stable configuration.
Exercise 13:
1Give ONE word/term for
1.1chlorine, bromine, iodine, fluorine and astatine. (1)
1.2group I elements. (1)
1.3needed when a positive ion is formed. (1)
1.4the name of the group to which copper belongs. (1)
1.5group VIII or 18 elements. (1)
1.6the amount of energy required to remove an electron from an atom in the gaseous phase.(1)
1.7the name of the group of metals to which copper belongs. (1)
1.8the name of the group of which neon is an example. (1)
2Which ONEof the following is a monatomic gas?
AChlorineBHydrogenCNeonDNitrogen (2)
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