Handbook c5 atomic structure by Agastya International Foundation

Agastya International Foundation

Atomic Structure Handbook C5

â&#x20AC;&#x153;When it comes to atoms, language can be used only as in poetry. The poet, too, is not nearly concerned with describing facts as with creating images. â&#x20AC;&#x153; - Neils Bohr (1885-1962)

Handbook C5 Atomic Structure OVERVIEW OF HANDBOOK ABL

CONCEPT

ABL1

Atoms and their composition

ABL2

Combination of atoms to form molecules and compounds Mole concept

ABL 3

NO. OF ACTIVITIES 4

PAGE NO. 3

ABLs WITH REFERENCE TO STANDARD SERIAL NUMBER 1 2 3

STANDARD 9, 10 9, 10 9, 10

RELEVANT ABL ABL1 ABL2 ABL3

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TIME (min)

LIST OF FIGURES, CHARTS AND WORKSHEETS

S. No Fig 1 Fig 2 Fig 3 Fig 4 Chart 1 Chart 2 Chart 3 Chart 4 Chart 5 Chart 6- flip chart Worksheet 1 Worksheet 2

Name Electronic configuration of Nitrogen Electronic configuration of Rubidium Puzzle cards Atomic mass representation Size comparison chart – Table 1 Size comparison chart – Table 2 Periodic table Bohr’s atomic model – 3D representation Electronic configuration chart Mole problems – 1,2,3,4 Organizer sheet 1 Organizer sheet 2

Page No 11 12 20 8 5 5 7 10 10 28 25 27

Note to Instructor: All the figures in this handbook are for the Instructor’s reference only. The Charts need to be printed and shown to the learners during the course of the activity. Worksheets need to be printed out in advance for the students. The number of worksheets required is mentioned in the Material List.

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ABL 1 – ATOMS AND THEIR COMPOSITION Activity

1.1

Learning Objective

How small is an atom?

Key Messages

Time (Min)



Atoms are smaller than anything that we can imagine. Size of an atom or Atomic radius is measured in nanometres

Atoms are different from each other based on the substance/ element that they form. Atoms of different elements are represented by specific symbols. Atoms of each element have a characteristic atomic mass One atomic mass unit (AMU) is equal to exactly one-twelfth the mass of one atom of carbon-12.

 

 1.2

Are all atoms the same?

 



1.3

What is an atom made up of?

An atom is made up of Protons, Neutrons and electrons  Neil Bohr’s model shows that atoms have positively charged protons and neutrons without charge in their nuclei.  Mass of an atom is the sum of the masses of protons and neutrons.  Electrons are negatively charged particles that revolve around the nucleus in specific orbits.  The number of electrons equals the number of protons in each atom and this number is the Atomic Number, which is characteristic to each element.  Valency is the combining capacity of an atom. Total Time

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4 Time: 15 min

ABL 1.1 LEARNING OBJECTIVE – How small is an atom? Note to Instructor – In this activity, please make sure you give the right size of paper to the learners at the beginning of the exercise. This will help them make the right comparisons later.

ADVANCE PREPARATION Material List S. No. 1 2 3 4 5

Material Paper Squares – 11’ X 11’ (28cm X 28cm) Scissors Meter rule Size comparison chart- Table 1 Size comparison chart- Table 2

Required Quantity 14 per class 14 per class 1 per class 1 per class 1 per class

Things to Do Cut the pieces of paper to 11’ X 11’ (28cm X 28cm) before the class and keep it ready for distribution. Safety Precautions Not Applicable

SESSION Link to known information/previous activity Let us do a simple experiment to understand how tiny things can be. Procedure Have a two-minute discussion with the class on what matter is made up of. Point to simple things in the classroom like books and pencils, and ask what their smallest unit could be. Facilitate this discussion till you get the answer ‘Atom’. Now ask them if they have ever seen an atom. Do they know how small an atom really is? Tell them that they will now perform a group activity to understand why we cannot see an atom and how small it really is. Tell them that in order to understand this activity, they must understand measurements. Show them the meter rule and tell them that this measures 1 meter. This will be a reference to explain the different measurements in the chart which has terms like nano, pico etc. [For example: if you take ten of these meter rules, you will get one decametre OR if you divide this meter rule into 100 equal parts, each part will form one centimetre]. You can ask the learners to give some examples of things from their Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies to handbooks.agastya@gmail.com

surroundings corresponding to each measurement so that they can connect those values to their daily lives. You can also refer to the examples given in Chart 2.

CHART 1 - SIZE COMPARISON CHART- Table 1

CHART 2 - SIZE COMPARISON CHART - Table 2 CUT 1 2 3 4 6 8 10 12 14

SIZE 14 cm 7 cm 3.5 cm 1.75 cm 0.44 cm 1 mm 0.25 mm 0.06 mm 0.015 mm

1 micron

500 nano-meters

COMPARISON Child's hand, pockets Fingers, ears, toes Watch, mushroom, eyes Keyboard keys, rings, insects

Mustard seeds Thread Fine pencil lead Hair, microscopic range Width of paper, microchip components Water purification openings, bacteria Visible light waves

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15 nano-meters

0.1 nano-meters

Electron microscope range, membranes The size of an ATOM!

Explain that the power (number superscript above 10) is the number of zeroes following 1 in the number we are multiplying or dividing by. When it is a division, the power has a minus sign. It is enough if you understand this much now to do the following activity. Put up the Size Comparison Chart-Table 2. Divide the learners into groups of three and follow these steps.   

  

Give each group the paper square (11’/11’) and scissors. Tell learners that if they can cut the square in half 31 times, they will be able to see how small ATOMS are. Tell them to fold the paper square and cut it into equal halves. Tell them to say “ONE” when they make the first cut. Notice that your square is now 14cm, which is approximately the size of a child’s hand, or a pocket. Tell them to look at Size Comparison Chart- Table 2. Now they should take one of the new pieces, and cut it into half saying “TWO”. Repeat this process by cutting one of the new pieces each time, and calling out the number of the cut. With each cut, ask them to refer to the size of the new paper and corresponding object in Table 2. Tell them to continue this process, cutting each new piece in half, until it is no longer possible. Each group should remember how many times they cut the paper before they had to stop. (Note to Instructor: Most groups will give up by cut 10.)

UNDERSTANDING THE ACTIVITY Leading Questions 1. What do you think all matter is made up of? What is the smallest particle/unit that you can think of? 2. Have you ever seen an atom? 3. Can we understand the size of the atom in relation to objects that we see in our daily life? Discussion and Explanation 1. All matter is made up of small particles called atoms. 2. We cannot see an atom, as it is extremely small. 3. Ask them to look carefully at Table 2. We can see that cut 10 brings us to 0.25mm, which is the size of a fine pencil lead. If we had been able to cut 12 times, we would have reached 0.06mm, which is the size of an average hair. (At this point, you can pass around a few rulers for them to see how tiny 1 mm really is.) We can see as we go down the table, at cut 18, we reach the size of a bacteria which cannot be seen by the naked eye. If we continue this way, at the 24 th cut, we reach 15 nanometres, which is the thickness of a cell membrane. Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies to handbooks.agastya@gmail.com

When we reach the 31st cut, we will reach 0.1nm, which is the size of an Atom. So you can imagine how tiny the atom is. The size of an atom is measured in nanometres. One nanometre is 109 meters.We measure the radius of the atom to indicate size. This is called atomic radius.

KEY MESSAGES:  Atoms are smaller than anything that we can imagine.  Size of an atom or Atomic radius is measured in nanometres. LEARNING CHECK: Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

WEB RESOURCE: http://www.spitzinc.com/pdfs/educ_guide_molecularium.pdf

ABL 1.2

Time: 15 min

LEARNING OBJECTIVE – Are all atoms the same? Note to Instructor –This activity is a quick discussion that should not take more than 10to 15 minutes. Spend maximum time on atomic mass and about 5 minutes on the rest.

ADVANCE PREPARATION Material List S. No. 1 2 3 4

Material Periodic table chart – Chart 3 Pencil and stick Sponge (or anything soft) and stone Atomic mass representation (cardboard circles)

Required Quantity 1 per class 1 per class 1 per class 1 set per class

Things to Do Not Applicable Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies to handbooks.agastya@gmail.com

Safety Precautions Not Applicable

SESSION Link to known information/previous activity In the previous activity we learnt that all matter is made up of very small units called atoms. Here we will find out if all atoms are the same. Procedure Pass the sponge and stone around the class and ask the learners to touch/feel and observe the objects. Ask the learners what these objects are made of. They should be able to tell you that it is made up of atoms. Now hold one in each hand and press hard. Next pass around the pencil and the stick and tell them to observe and think what these objects are made of. Ask them a set of leading questions about these things that will help them understand atoms better.

UNDERSTANDING THE ACTIVITY Leading Questions 1. 2. 3. 4.

What happened when the sponge and stone were pressed? Why? Can you write with the stick in the same way that you can write with the pencil? Why? Why do you think these things show these differences? Doatoms of all elements have the same mass? (Take a vote by raise of hands to make learners feel more involved.) 5. How do you think atomic mass is measured? Discussion and Explanation 1. The sponge being soft changes shape and the stone, being hard, did not because they are made of different materials. 2. We cannot write with the stick as the lead inside the pencil is the material that helps us to write. 3. Each of these materials is made of different atoms with different properties. A material/substance made of one specific type of atoms is called an element. We recognize these elements by a specific name. These names come from the Latin or Greek words that were used for these elements. Ex: Graphite is the name given to the element inside your pencil. The property of this element allows it to write on paper. The names of these elements with some of their properties are listed in a table called the periodic table (SHOW THE PERIODIC TABLE). The names of elements are all given short symbols which are mostly one or two letters taken from their name. This makes it easy for us to use them in the study of higher chemistry. These symbols are taken from their English names â&#x20AC;&#x201C; for example, the symbol Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies to handbooks.agastya@gmail.com

for Carbon is C; Sometimes the symbol is taken from the Latin name of the element, for example, the symbol for Silver is Ag, taken from its Latin name Argentum. Note to Instructor: reference – C6 - Periodic Table ABL 1.1 4. Different atoms have different properties and therefore their mass is also different. This is called atomic mass and is unique to each element. 5. Because atoms are so tiny, it was difficult to find a unit like Kg etc. to measure atomic mass. Therefore, scientists decided to use an atom of carbon as a reference to measure atomic mass. Imagine you have an atom of Carbon (show one circle). This atom was then divided into twelve. (Show pieces or cut the carbon atom into twelve equal parts). The mass of each unit was said to be one atomic mass unit/ 1 Amu. The mass of each of these units was taken as reference and the mass of all other elements was found relative to these units.

Figure 4 – Atomic mass representation For example, indicate a weighing balance with your hands and put one of the pieces on one palm and an imaginary element like oxygen on the other. Explain that oxygen was found to be 16 times as heavy as that one piece and hence the atomic mass of oxygen was found to be 16 Amu. (This means that an atom of oxygen has a mass that is 16 times the mass of 1/12th atom of carbon.)

KEY MESSAGES:  

Atoms are different from each other based on the substance/ element that they form. Atoms of different elements are represented by specific symbols.

 Atoms of each element have a characteristic atomic mass.  One atomic mass unit (AMU) is equal to exactly one-twelfth the mass of one atom of carbon-12. The atomic masses of all elements have been found relative to this.

LEARNING CHECK: If an atom of nitrogen has a mass that is fourteen times that of 1/12th the mass of an atom of carbon, then what is its atomic mass? (Answer for Instructor’s reference –14) Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies to handbooks.agastya@gmail.com

TRY IT YOURSELF: Ask 10th standard students to go home and check in their texts, how many elements have symbols derived from other languages in the periodic table. Time: 30 min

ABL 1.3 LEARNING OBJECTIVE – What is an atom made of?

Note to Instructor–Please keep the explanation within ten minutes so that learners have enough time for trying out the activity.

ADVANCE PREPARATION Material List S. No.

Material

3-D representation chart of Bohr’s atomic model Slates Chalk Small red buttons Small blue buttons Small yellow buttons Periodic table chart Electronic configuration chart (Image source http://commons.wikimedia.org)

2 3 4 5 6 7 8

Things to Do Make sure all the material is in order before you start the activity. Safety Precautions Not Applicable

SESSION Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies to handbooks.agastya@gmail.com

Required Quantity 1 per class 10 per class 10 pieces 150 pieces 150 pieces 150 pieces 1 per class 1 per class

Link to known information/previous activity We now know that atoms have specific properties like atomic radius and atomic mass. Now let us see if there are even smaller structures that make up an atom. Procedure Note to Instructor – If the group is aware of the information that you are going to share in the following section, try and involve learners by asking questions and involving them as much as possible. Ask the classwhether an atom can be divided into even smaller parts. Explain that it cannot easily be broken up further, but it consists of three kinds of sub-atomic particles: -The Proton, which has a positive charge. -The Neutron, which has no charge. -The Electron, which has a negative charge. Neil Bohr proposed a model for the arrangement of these sub-atomic particles. Now put up the chart of the Bohr’s model, and explain the following points:

CHART 4 – Bohr’s atomic model – 3D view (Image source - http://commons.wikimedia.org)     

Every atom has a nucleus where most of its mass is concentrated. All the protons and neutrons are in the nucleus of the atom.The total number of protons and neutrons in an atom is called the mass number. The number of protons in an atom is unique to that particular element. This is called the atomic number. The Atomic mass of an atom is the sum of the total mass of the protons and neutrons. The third sub-atomic particle is the Electron, which has a negligible mass and a negative charge. The electrons are equal in number to the protons and revolve around the nucleus in specific paths called orbits or shells. The orbits get bigger as you move away from the nucleus and they have an almost circular shape called an ellipse. Only to understand it easily, we draw the orbits as concentric circles. The orbit

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

closest to the nucleus is known as the ‘K’ orbit or ‘K Shell’. The next orbits are known as L, M, N and so on. Now divide the class into 10 groups and give each group a slate and some chalk. Ask them to draw a central nucleus and four concentric circles around it, and label the shells as you have explained. Note to Instructor: An example is given below for your reference:

Figure 1 – Electronic configuration of Nitrogen (Image source - http://commons.wikimedia.org)   

   

Now explain the following: You can see from the Bohr’s model that different electrons are in different orbits. How do we know how the electrons are distributed in the different shells of an atom? This arrangement is not random, but specific to each kind of atom to make it a stable structure. This arrangement of electrons in the different orbits of an atom is called the electronic configuration. The electrons fill up the shells in a step-wise manner starting with the K shell or the first shell. This shell can only take 2 electrons. The remaining electrons are sent to the outer shells. Now the next shell-the L shell- can accommodate 8 electrons. Think of an atom that has 2 electrons in the K shell and 8 electrons in the L shell, but still has some electrons left. These will now go to the third or M shell. So how do we find out how many electrons can fit in any given shell? There is a formula for finding out how many electrons a shell can accommodate. This is 2n2, where n is the position of a shell. For example, L is the second shell, so n=2. Therefore, the number of electrons it can take is 2X22 =8 If n=3 (M shell), 2n2=2X(3)2=18. So the M shell can have a maximum of 18 electrons. However, the maximum number of electrons that the outermost shell can accommodate is always 8. Give example of rubidium where the electrons in the fourth shell (9 remaining) get split into 8 and 1.

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Figure 2 – Electronic configuration of Rubidium (Image source - http://commons.wikimedia.org) 

The data of the atomic mass and number for each element is given in the periodic table that we saw in ABL 1.1. Show them a particular element and show them where the atomic number and atomic mass of each element is written.

Now let us use the concentric circles on your slates to understand some more about the electronic configuration. Each group will now get 15 red buttons for electrons, 15 blue buttons for protons and 15 yellow buttons for neutrons. Tell them that you will work with them on the first example.Let us take the element Neon, which is written as– Ne1020.Here, Ne is the symbol for Neon, 10 is the atomic number, and 20 is the mass number. Having given this information, ask each group to pick the right number of buttons for protons, neutrons and electrons in Neon. Note to Instructor: Learners must take 10 buttons of each colour to represent the atom of Neon. Now with the information that you know, place the electrons, neutrons and protons on your drawing of the atom. You will get five minutes to complete the activity. Note to Instructor: Learners must pile up the ten protons and neutrons within the nucleus and distribute the electrons as 2 in the first shell and 8 in the second shell. They should leave the third and fourth shell empty. If they are unable to do this, help the groups to get the correct arrangement. UNDERSTANDING THE ACTIVITY 1: Leading questions 1: 1. 2. 3. 4. 5. 6.

What is the number of protons in Neon? What is the number of electrons in Neon? What is the number of neutrons in Neon? How many electrons go in shell 1? How many electrons go in shell 2? Are there any electrons left?

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Discussion and Explanation 1: 1. 2. 3. 4. 5. 6.

The number of protons in Neon is the atomic number, whichis 10. The number of electrons in Neon equals the number of protons, which is 10. The number of neutrons in Neon is the mass number – atomic number = 10. The first shell will have 2 electrons. The second shell will have 10-2 = 8 electrons. No electrons are left so the third shell remains empty.

Once they have completed this, assign a different element to each group and give them five to ten minutes arrange the buttons correctly.At the end of the exercise, put up the ‘Electronic Configuration’ Chart – Chart 5. The entire class will now compare their slates with the corresponding electronic configuration in the chart. After they complete the activity, take five minutes to explain valency using the leading questions.

UNDERSTANDING THE ACTIVITY 2 Leading Questions 2: 1. As we already know, the maximum number of electrons in the outermost shell cannot be more than 8. But did you notice cases where electrons in the outermost shell did not add up to eight? Discussion and Explanation 2 1. Yes, there are cases where the outermost shell does not fill completely. In this case, that outermost shell can accommodate more electrons. Their electrons can come from another atom of another element. This gives the atom an ability to combine with other elements that can give it electrons or take electrons from it. Atoms that have complete outermost shells (also called valence shells) are stable and show no chemical activity. Other atoms, that do not have a complete outermost shell, will react with each other by gaining or giving away electrons to attain a stable state with a complete valence shell. For example: sodium has an electronic configuration of 2,8,1. Its valence shell has 1 electron. Hence it can give away one electron to attain stability. This number of electrons that it can give away is called its valency. Since it is giving away a negative charge, its valency is +1.Chlorine has an electronic configuration of 2,8,7. Its outermost shell has 7 electrons. So it needs to gain one electron to achieve a stable configuration. Since it will get one electron/negative charge, its valency is -1. Thus, valency is the combining capacity of an atom.

KEY MESSAGES: Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies to handbooks.agastya@gmail.com

     

An atom is made up of Protons, Neutrons and Electrons. Neil Bohr’s model shows that atoms have positively charged protons and neutrons without charge in their nuclei. Mass of an atom is the sum of the masses of protons and neutrons. Electrons are negatively charged particles that revolve around the nucleus in specific orbits. The number of electrons equals the number of protons in each atom and this number is the Atomic Number, which is characteristic to each element. Valency is the combining capacity of an atom.

LEARNING CHECK: If time permits you can point out an element in the periodic table and ask them to do the configuration and tell you the valency of that atom as an evaluation.

TRY IT YOURSELF: Use household items to try out the electronic configuration for elements with higher atomic numbers in the periodic table. You can also just draw it out and use coloured pens or pencils to mark the electrons.

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ABL 2– HOW DO ATOMS COMBINE? Activity

Learning Objective

Key Messages

Time (Min)



An ion is a charged particle that can be positively or negatively charged and is formed when an atom loses or gains electrons Many atoms combine to form molecules so that they can exist in a stable form. If atoms of the same element combine, the molecule of an element is formed If atoms of different elements combine, the molecule of a compound is formed.

The valency of atoms helps to determine how they will combine to form a compound.  A chemical formula is a symbolic representation of the composition of a compound.  We can write a chemical formula using the symbols and the valency of the atoms in a compound. Total Time

 2.1

What are molecules and ions?

 



2.2

What is a chemical formula and how do you write it?

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ABL 2.1

Time: 20 min

LEARNING OBJECTIVE – What are ions and molecule? Note to Instructor – In this activity we will only be introducing how ions and molecules are formed. All bonds will only be of one type and will be referred to as “bond”. We will not be getting into covalent and ionic bonds.

ADVANCE PREPARATION Material List Sl.No. 1 2

Material Ball and Stick Model Electronic configuration chart (from ABL 1.3) – Chart 5

Required Quantity 10 each 1 set per class

Things to Do Not Applicable Safety Precautions Not Applicable

SESSION Link to known information/previous activity In ABL 1.3 we learnt about valency, which is the combining capacity of atoms. The number of electrons that an atom is capable of gaining or losing when its valence shell is not full is called its valency. Here we will see how exactly atoms become stable. Procedure Explain that atoms will always try to have a complete valence (outermost) shell with eight electrons so as to be stable. In order to have a complete valence shell, they may gain or lose electrons. Atoms are electrically neutral because they have the same number of negative charges (electrons) and positive charges (protons). But when they gain or lose electrons,the number of electrons will no longer be the same as the number of protons. Because of this, the atom will become a charged particle, which is called an ION. Now use the chart of the electronic configuration chart to explain the cases of Sodium and Chlorine. Sodium has one electron in the valence shell and it will be easy for it to lose this and be stable. When Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies to handbooks.agastya@gmail.com

the sodium ion loses its electron it has one extra positive charge and hence becomes a positively charged ion. Positively charged ions are called cations. Similarly, Chlorine has seven electrons in its valence shell. It is easy for Chlorine to gain one electron (instead of losing 7 electrons) in order to become stable. This will give it one extra negative charge and make it a negatively charged ion. Negatively charged ions are called anions. Now using the ‘Electronic Configuration’ chart (from ABL1.3) – Chart 5, go to the leading questions.

UNDERSTANDING THE ACTIVITY Leading Questions 1. 2. 3. 4.

What kind of ion do you think aluminium will form? What charge will it take? What kind of ion do you think fluorine will form? What charge will it take? How do you think these ions actually combine with other to gain or lose electrons? Is ionic bonding the only way to form a molecule?

Discussion and Explanation 1. Aluminium has three electrons to give away and hence, will form a cation with a charge of 3+ 2. Fluorine will gain one electron and will form an anion with a charge of -1 3. Ions come together with ions formed from other atoms and form bonds with each other in order to be stable. These bonds are called ionic bonds. And the group of two or more atoms that combine together using these bonds form a molecule. For example, (show on the chart), sodium having +1 charge will form and ionic bond with chlorine having a -1 charge to form a compound called sodium chloride. 4. Some atoms do not form ions but actually share electrons with other atoms to form molecules. These atoms also form bonds within the molecule called covalent bonds. Atoms of the same element can form molecules. For example, two atoms of oxygen combine to form one oxygen molecule so that they can exist stably. (Use the ball and stick model, with two identical balls to show similar atoms combining to form a molecule.) Atoms of different elements that bond together can also form molecules. Ex: water is formed when oxygen and hydrogen atoms share electrons to form a stable structure. Looking at the electronic configuration of hydrogen and oxygen, we can see that oxygen needs two valence electrons but hydrogen has only one. Therefore, two hydrogen atoms come together to bond with one atom of oxygen by giving it one electron each to form a stable structure. (Use two different coloured balls to show Hydrogen and Oxygen in the water molecule)

KEY MESSAGES:   

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

If atoms of different elements combine, the molecule of a compound is formed.

LEARNING CHECK: Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation.

Time: 30 min (15 +15)

ABL 2.2

LEARNING OBJECTIVE – What is a chemical formula and how do we write it? Note to Instructor – In this activity, 2.2a is only to illustrate how atoms share electrons and is a good way to explain why we do the crossing of valency to write a chemical formula. If time does not permit, this activity may be skipped.

ADVANCE PREPARATION Material List Sl.No. 1 2 3 4

Material Marbles Plastic cups Configuration chart Puzzle cards of different elements

Required Quantity 30 per class 6 per class 1 per class 1 set per group

Things to Do Not Applicable Safety Precautions Not Applicable

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Link to known information/previous activity In the previous discussion, we saw that atoms bond with each other based on their valency to form stable compounds. Now let us see how we represent these compounds. SESSION 2.2a Procedure Explain to the learners that they will now play a small game that will help them understand how atoms share electrons. The Marble Game: Purpose: learners will begin to understand the principle of electrontransfer as they transfer marbles to one another and form groups in order to satisfy the conditions stated bythe Instructor. 1) Choose 18 learners and give 1 small cup to each learner, four marbles for half of the learners (the otherhalf of the learners get no marbles – just an empty cup). 2) Learners who have marbles are told that they are the marble givers while thosewithout marbles are told that they are the marble acceptors. 3) When a giver wants to give amarble to an acceptor he must place the marble in the acceptors cup and then must remainnext to the acceptor. Each giver must give as many marbles as possible to a single acceptor and only them must he/she consider giving marbles to another acceptor. An acceptor can take marbles from more than one giver. 4) When a group of learners believe they have satisfied the Instructor’s conditions, they must raise their hands, and the Instructor will check to see if they are correct. (Ask the other learners to observe and then try it once with other learners while the first batch of learners observe) Game Play: 1) Instructor calls out the conditions: e.g. Each GIVER must give 3 marbles; Each ACCEPTOR must accept 2 marbles.Begin with easy conditions: e.g. Each GIVER must give 1 marble; EachACCEPTOR must accept 1 marble. 2) Learners must begin the transfer process as givers and acceptors interact: e.g. in the situation above learners will have to realize that there need to be 3 givers and 2acceptors in order to satisfy the conditions stated. (So all these five children should be standing together as a group at the end) 3) When a group of learners raises their hands, check to make sure they havetransferred the marbles correctly. 4) Discuss with entire class how to arrive at correct grouping of GIVERS andACCEPTORS. NOTE: Before calling out each new condition, please make sure the learners give the marbles back to the givers and acceptor cups are empty and givers have four marbles as they did initially. CONDITIONS AND SOLUTIONS – EXAMPLES 1) Each giver must give one marble and acceptor must accept one marble – At the end, the learners must be standing in pairs of one giver and one acceptor. Giver will Have 3 marbles and acceptor will have one. This is similar to NaCl. Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies to handbooks.agastya@gmail.com

2) Each giver must give one marble and acceptor must accept two marbles – At the end, the learners must be standing in groups of three with 2 givers and one acceptor. Givers will Have 3 marbles and acceptor will have two. This is similar to water molecules, Copper Oxide etc. 3) Each giver must give 3 marbles and acceptor must accept 2 marbles – At the end, the learners must be standing in groups of five with two givers and three acceptors. Giver will have 1 marble left and acceptor will have three.

UNDERSTANDING THE ACTIVITY Leading Questions 1. In every case, were the number of givers and acceptors the same? 2. If the givers are one kind of atom and the acceptors are another kind of atom, what are the marbles and do you think defines the instruction that the Instructor gave? Discussion and Explanation 1. The number of givers and acceptors are very different in each case. It depends on the combination that allows them to satisfy the condition given by the Instructor. 2. The marbles symbolize electrons and the condition stated by the Instructor is nothing but the valency of the atoms. This shows us that the valencies of the atoms that form that compound determine the chemical formula of a compound. SESSION 2.2b Procedure Explain to the learners that they will now try writing chemical formulae for compounds. Tell them that they will first try it with a few puzzle cards that will represent the molecules. Show them with an example,

Figure 3 – Puzzle cards Here, sodium and chlorine have only one groove (valency is 1) each and hence only one Sodium atom is needed to combine with one chlorine atom to give Sodium chloride. When we write it as a chemical formula, we write the symbols of the elements beside each other (symbol of metal first followed by the non-metal)with a subscript that shows the number of atoms. This number is the number of atoms of that element that combine to form the compound molecule. Here it will be – Na1Cl1. Since the subscripts are 1, we can write it as NaCl. Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies to handbooks.agastya@gmail.com

Take a moment to explain that there are polyatomic ions like OH- that can be considered as one entity by the learners by the use of a bracket. Divide the class into groups and give each group one set of puzzle cards. Now call out the following element pairs one by one. Ask learners to combine them in such a way that all the grooves fit into each other. 1) 2) 3) 4)

Hydrogen and chlorine Aluminium and oxygen Magnesium and chlorine Calcium and hydroxide

Answer for Instructor reference: Answers- 1) HCl 2) Al2O3 3) MgCl2 4)Ca(OH)2 Now ask the groups to write down the formula for the compound depending on how many atoms were needed to form it.

UNDERSTANDING THE ACTIVITY Leading Questions 1. Are the two elements in the compounds we just made similar to each other? 2. What do the numbers in the subscripts of the chemical formulae show?

Discussion and Explanation 1. No, the two elements are not similar. Every compound has a metal combining with a non-metal. There was no case where two metals found a way to combine with each other. 2. The numbers in the subscripts define the number of atoms of that element that are required to satisfy the valence electrons of the other element in the compound. This is also the number of atoms of that element that are present in the molecule.

Now tell the learners the following: Puzzle cards and games help us understand how atoms combine. We can also use a simple crisscross technique to write chemical formulae. Here, we simply write the valencies as charges and exchange the valencies between the two combining atoms. This serves as a quick shortcut to use in class. Use the following examples to indicate this:

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(Image source - http://commons.wikimedia.org)

KEY MESSAGES:  

The valency of atoms helps to determine how they will combine to form a compound. A chemical formula is a symbolic representation of the composition of a compound.

 We can write a chemical formula using the symbols and the valency of the atoms in a compound. LEARNING CHECK: Ask learners to list the key things they have learnt. Guide them to the key messages listed and then put up the key messages chart. If you have time during the class, make up a small game or quiz or match the following as a learning check. This may have to be done as part of advance preparation. Note to Instructor – Take about 10 minutes to discuss the interesting information with the students after a quick learning check.

INTERESTING INFORMATION: ISOTOPES AND ISOBARS We have learnt about atoms, molecules and ions. Another form in which we find atoms is as Isotopes and Isobars. What are isotopes and isobars? We have learnt about atoms having an atomic number and a mass number. We know from ABL1 that the atomic number is unique to an element but this is not the case for the mass number. There are a few cases where the atoms of the same element will have the same atomic number but different mass numbers. These are called isotopes of the same element. Isotopes do not differ much in chemical properties and so can be considered the same in mixtures but one area of interest is that some isotopes show very interesting applications: 1) An isotope of uranium is used as a fuel in nuclear reactors 2) An isotope of cobalt is used in treatment of cancer 3) An isotope of iodine is used in treatment of goitre For these reasons the interest of scientist in isotopes is increasing in today’s world. Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies to handbooks.agastya@gmail.com

Isobars â&#x20AC;&#x201C; sometimes there are atoms of two different elements which have different atomic numbers but happen to have the same mass number. These are called isobars. Ex:Calcium and Argon with atomic numbers 20 and 18 respectively, both have a mass number of 40.

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ABL 3– MOLE CONCEPT Activity

Learning Objective

3.1

What is the relation between mole and number of molecules?

Key Messages

Time (Min)



A mole is a standard unit of counting in chemistry. One mole of a substance always contains 6.022 X 1023 molecules of that substance.

 3.2

What is the relation between mole and mass?

Evaluation

Mole is a standard unit to measure mass in chemistry.  One mole of a substance always contains one gram molecular mass or molar mass of that substance.  Mole concept problems from syllabus Total Time

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15 55

ABL 3.1

Time: 20 min

LEARNING OBJECTIVE – What is the relation between mole and number of molecules? Note to Instructor – In this activity we will introduce an imaginary counting unit to help learners understand the concept of mole as a standard unit of measuring number in chemistry. Please use the term‘mole’only after learners are comfortable with the concept of a standard unit.

ADVANCE PREPARATION Material List S.No. 1 2 3 4

Material A bag of chocolates (20 chocolates) A bag of buttons/blocks (24 buttons) A bag of erasers (or any other object) (15 erasers) Organizer sheet 1

Required Quantity 1 per class 1 per class 1 per class 1 per learner

Things to Do Print copies of organizer sheets for learners. Each sheet will have three organizers so you need not print too many copies. Safety Precautions Not Applicable

SESSION Link to known information/previous activity Not Applicable Procedure Explain the concept of a unit of measure as follows: when you buy eggs you usually ask for a __dozen___ eggs? When you buy milk, you ask for a __litre___ of milk. These words are standards of measurement that have been created to make our lives easier. We know that a dozen is always twelve of anything. We know that a litre is a standard amount of any liquid that it may measure. Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies to handbooks.agastya@gmail.com

Now imagine that you have a chance to create your own unit of measure today. What would you name it and what would be its standard? Ask learners to suggest a name. Let us assume they say the unit will be named STAR. And each star will contain four items. (Take both these suggestion from the learners). Make sure they do not give a number higher than ten as a measure of a single unit. Now tell learners that their unit can now be used to count anything. To try this out, call volunteers to count the number of sweets, buttons and erasers in each bag. Have two sets of learners repeat it for each bag and write down the results of the count on the board. Hand out the organizers and ask learners to ask write down the count.

Name of items Sweets Buttons Erasers

Number

Tell them that since they know that one STAR has 4 units â&#x20AC;&#x201C; Make them write this down. They need use this to do a few calculations for you. Call out each question (leading questions) and take an answer from the learners and move on. If the learners need to write for the tougher questions, they may do so at the back of the organizer. Answers in decimal are accepted.

UNDERSTANDING THE ACTIVITY Leading Questions 1 1. 2. 3. 4. 5. 6. 7. 8. 9.

How many oranges are there in one STAR of oranges? How many atoms of iron are there in one STAR of iron? How many buttons are there in one STAR of buttons? How many erasers are there on 6 STARS of erasers? How many sweets are there in a Â˝ STAR of sweets? How many STARS as 100 sweets? How many STARS are 40 books? How many STARS is 2 buttons? How many STARS of erasers did they measure?

Discussion and Explanation1 1. 2. 3. 4. 5.

4 oranges 4 atoms 4 buttons 24 erasers 2 sweets

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6. 7. 8. 9.

25 STARS 10 STARS 0.5 STARS No. Of erasers / 4

Now explain the following – Similar to the star always measuring a count of four, in chemistry there is a similar standard unit to count units like molecules and atoms and all other substances. But since atoms are so small the standard number is much higher than 4. Here1 mole = 6.022 X 1023 units.

Leading Questions 2 1. How many sweets make up one mole? (Ask after explaining mole) 2. How many atoms of sodium are in two moles? 3. How many moles of pens are 12.04 X 1023number of pens? Discussion and Explanation 2 1. 6.022 X 1023 sweets make up a mole 2. 12.04 X 1023 atoms of sodium 3. 2 moles of pens

KEY MESSAGES:  

A mole is a standard unit of counting in chemistry. One mole of a substance always contains 6.022 X 1023 molecules of that substance.

LEARNING CHECK: 1. How many molecules of water, make up five moles? 2. How many moles are in 6.022 X 1023 atoms of any substance?Answers for Instructor’s reference – 1. 30.1 X 1023 molecules of water 2. 1 mole

ABL 3.2

Time: 20 min

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LEARNING OBJECTIVE â&#x20AC;&#x201C; What is the relation between mole and mass? Note to Instructor â&#x20AC;&#x201C; In this activity we will introduce an imaginary counting unit to help learners understand the concept of mole as a standard unit of measuring mass in chemistry. Try not to use mole in the beginning of the explanation till learners are comfortable with the concept of a standard unit.

ADVANCE PREPARATION Material List Sl.No. 1 2 3 4 5 6

Material A bag of chocolates A bag of buttons/blocks A bag of erasers (or any other object) Weighing balance Organizer sheet 2 Evaluation flashcards with one problem on each (flip-chart of 4)

Required Quantity 1 per class 1 per class 1 per class 1 per class 1 per learner 1 set per class

Things to Do Print copies of organizer sheets for learners. Each sheet will have three organizers so you may not need to print too many copies. Safety Precautions Not Applicable

SESSION Link to known information/previous activity We have already created our own unit, the STAR in the previous activity as a standard to count the number of any item. Now, we will use the STAR as a unit to measure mass. Procedure Since we know that one star is 4 units. Let us measure the mass of one STAR (four pieces) of sweets, buttons and erasers. Have learners count four pieces out and weight them and note it down in the table. Name of items Sweets Buttons Erasers

Mass of one STAR (in gms)

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Tell them that they will notice there is a difference here. The mass of one STAR is a standard specific amount for a particular substance only. (Not in general like before). Ex: the mass of one STAR of sweets is not the same is the mass of one STAR of buttons even thought the count is the same. They need use this to do a few calculations for you. Call out each question (leading questions) and move on to the next after the class responds. If the learners need to write for the tougher questions, they may do so at the back of the organizer. Answers in decimal are also accepted. The questions and answers must progress fast.

UNDERSTANDING THE ACTIVITY Leading Questions 1. 2. 3. 4. 5.

What is the mass of 2 STARS of sweets? What is the mass of 100 STARS of buttons? What is the mass of 0.5 STARS of erasers? How many STARS is 400gms of sweets? How many STARS is 1000gms of erasers?

Discussion and Explanation1 1. 2. 3. 4. 5.

2 X measured weight 100 X measured weight 0.5 X measured weight 400 / measured weight 1000 / measured weight

Similar to our STAR, the mole also applies to mass. The mole is a standard measure of mass for a particular substance. This standard measure for a substance can be found out by finding the gram atomic mass or Molar mass of that substance. [Demonstrate how this is done for a substance – H2O will be = (atomic mass of hydrogen X 2) + Atomic mass of oxygen = 2+16 = 18g. This means that one mole of water contains 18g of water in it. This will always be a standard unit of measuring the mass of water. This standard can thus be found in the same way for all substances. Leading Questions 2 1. Find the mass of three moles of each of the following – Ca(OH)2 , H2SO4, Al(NO3)3 [ Ask after the explanation and give learners five minutes to solve it. Provide them with the atomic weights of the elements on a board.] Atomic weights of elements: Calcium – 40 Oxygen - 16 Hydrogen - 1 Agastya International Foundation. For Internal Circulation only. Request to Readers- Kindly mail details of any discrepancies to handbooks.agastya@gmail.com

Sulphur - 32 Aluminium - 27 Nitrogen - 14 Discussion and Explanation 2: 1. Answer key: The mass of three moles of Ca(OH)2is – 222g (74 X 3) The mass of three moles of H2SO4is – 294g (98 X 3) The mass of three moles of Al(NO3)3is – 639g ( 213 X 3)

KEY MESSAGES:  

Mole is a standard unit to measure mass in chemistry. One mole of a substance always contains one gram molecular mass or molar mass of that substance.

LEARNING CHECK: If time permits, put up flash cards with one or two mixed problems on mole concept based on syllabus and have learners solve it in pairs for about ten minutes. You can even divide the learners into four groups and have four corners of the room with one flash card in each corner. Learners can go from one station to another as they solve the problems and aim to finish all the stations in ten minutes.

WEB RESOURCES: http://www.terrificscience.org/lessonpdfs/MoleIntro.pdf

REFERENCES: 1) 2) 3) 4)

National Council of Educational Research and Training, Class IX, October 2013 National Council of Educational Research and Training, Class X, November 2012 Stage 1 – Chemistry – ‘O’ level – Nuffield foundation, Heinemann Educational Books Ltd., 1978 Introduction to the Mole- By Golda Steiner, Park Ridge High School, Park Ridge, NJ: Developed through the National Science Foundation-funded Partnership for the Advancement of Chemical Technology (PACT)

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APPENDIX ELECTRONIC CONFIGUATION CHART

ATOMIC NUMBER

ELECTRONIC CONFIGURATION DIAGRAM

ELECTRONIC CONFIGURATION IN WORDS

1 1 2

2,1

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2,2

2,3

2,4

2,5

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2,6

2,7

2,8

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2,8,1

2,8.2

2,8,3

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2,8,4

2,8,5

2,8,6

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2,8,7

2,8,8

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