ATOMIC THEORY Chemistry Unit
The Atomic theory unit covers...how our understanding of how the universe came to be...how everything is made of tiny things called atoms...
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Black Boxes & the Heart of the Atom Models are used to help us visualize atoms. Atoms are so small that it is impossible to see them. The following chart presents the assumed diameters of some atoms:
Atom
Diameter
Hydrogen Lithium Nickel
6.2 x 10-11 m 3.0 x 10-10 m 2.5 x 10-10 m
This means that across the diameter of a nickel, there are about 8.0 x 107 atoms or 80 000 000 atoms.
The whole top surface of the nickel would have about 5.0 x 1015 atoms on it! Scientists call an unobservable object, such as an atom, a BLACK BOX. There are many examples of black boxes in everyday life. One example of this is a pop machine, if you have never seen the inside of one. However you do know something about a pop machine because of the experiments you have performed on the machine, you usual receive a can of pop. Therefore, you have a mental picture or model of what must go on inside a pop machine. To find out more about the inside of this type of machine, you would have to come up with a hypothesis or idea of how the machine actually works and then test your hypothesis many times to see if you could complete or add to your model. You have been given a black box. It is not empty. The object of this activity is for you to examine the box in every possible way you can think of and learn as much as you can about the inside of the box. Do not damage or open the box.
Observations Observations
Inferences
The Black Box In the space below and using your observations and inferences, clearly draw what you think the inside of the box looks like. Clearly label your diagram (to scale) and give reasons for the contents the black box.
Box Letter: Diagram Scale:
QUESTIONS 1. Were any of the objects in the box round? Did any of the objects roll smoothly as you tilted the box? How do you know?
2. Did the objects make a noise when they collided? If so, how many? How do you know?
3. Were any of the objects attracted by a magnet? If so, how many? How do you know?
4. Could you tell the number of objects in the box by the sounds made as the box is moved or by the way the objects moved when the box was tilted?
5. As you gradually tilt the box do all the objects in it begin to move at the same time?
6. What other questions can you ask yourself about the contents of the box?
7. Without ever opening the box to peer inside, how would you prove that your model of the inside of the box was correct?
The Atomic Theory Story... Greeks
Billiard Ball
Raisin Bun
Rutherford
Bohr
Quantum Mechanics
String Theory?
GUT?
?
? 900 BC labs of the mind
1803
1890 cathode ray tubes
1911 Gold Foil Experiment
1920
1920 - present
21C
22 C
atoms
atoms
electrons (e)
electrons (e) protons(p) neutrons(n)
electrons (e) protons(p) neutrons(n)
electrons (e) protons(p) neutrons(n) gluons quarks neutrinos muon tau gluon
superstrings? Higgs boson?
gravitons? tachyons? dark matter?
The Standard Model
The Bohr Diagram
Bohr Diagram (expanded)
Bohr Diagram (condensed)
Atomic Notation (ZXA) Atomic Mass Number (A) = # of protons + # of neutrons Atomic Number (Z) = # of electrons = # of protons (A) > (Z) All atoms are NEUTRAL (X0) if the number of electrons = number of protons, since the number of negative charges balance out the number of positive charges.
Electron Arrangement in Atoms 1. The outermost energy level (farthest from the nucleus) can have up to a maximum of 8 electrons. (Octet Rule) 2
2. The maximum number of electrons in all inner energy levels is determined by 2n (n, represents the number of the energy level)
outermost energy level ‌ fourth energy level third energy level second energy level first energy level
n=4 n=3 n=2 n=1
nucleus
8 electrons ‌ 2 2 2n = 2(4) = 32 electrons 2n2 = 2(3)2 = 18 electrons 2n2 = 2(2)2 = 8 electrons 2n2 = 2(1)2 = 2 electrons
How to Draw a Bohr Diagram
Bohr Diagram Practice Draw the Bohr diagrams for the following elements:
23
Na11 (Na0)
35
Cl17 (Cl0)
10
Mg12 (Mg0)
40
Ar18 (Ar0)
B5 (B0)
14
P15 (P0)
1
Kr36 (Kr0)
12
31
84
24
N7 (N0)
H1 (H0)
C6 (C0)
27
Al13 (Al0)
39
K19 (K0)
40
Si14 (Si0)
32
S16 (S0)
Ca20 (Ca0)
64
Cu29 (Cu0)
O8 (O0)
19
F9 (F0)
20
Ne10 (Ne0)
He2 (He0)
7
Li3 (Li0)
9
16
4
28
Be4 (Be0)
Bohr Model – Atomic Particles Practice Element Name
Element Symbol
Mass Number
Atomic Atomic Number Notation
Number Number Number of of of electrons protons neutrons
H He Lithium
Li Be B C N O F Ne Na Mg Al Si P S Cl Ar
7
3
3
Li7
3
3
(7-3) = 4
Bohr Model – Atomic Particles Practice 2 Element Name
Element Symbol
Mass Number
Atomic Atomic Number Notation
Number Number Number of of of electrons protons neutrons
19 20 23
V51
Cr 55 26 Co 28 29 65 75
As33
bromine
Kr 88 56 47 aurum
53
Atomic Mass Challenge
Determine the mass of a single unit in the sample that you have been given.
Questions 1. Find the mass of 1 bean if 20 beans have a mass of 44g.
2. Twelve peas have a mass of 48 g. Find the mass of 6 peas.
3. Find the mass of 100 grains of rice if 250 grains have a mass of 7.5 g.
4. A mass of 60 g of beans contains how many beans, if each one has a mass of 0.3 g?
5. The mass of 1 grain of rice is 0.020 g. How many grains are in 0.453 kg?
6. The mass of 6.02 x 1023 atoms of copper is 63.5 g. Find the mass of one atom.
Beanium Activity Sample #:
To practice the concept of isotopes using a sample of Beanium. Total number of "atoms" in the Beanium sample =
Measured total mass of sample =
kidney bean isotope
soya bean isotope
pinto bean isotope
Number of isotope "atoms"
Total mass of each isotope
Average mass of one isotope atom average mass = total mass รท number
Numerical percentage (%) of each isotope % = (part รท whole) x 100
Calculated average mass (weighted) of one atom of Beanium = calculated average mass (weighted) = [(% isotope 1) x (average mass of one atom of isotope 1) + (% isotope 2) x (average mass of one atom of isotope 2) + .... (% isotope n x average mass of one atom of isotope n)] รท100
Calculated total mass of Beanium sample = calculated total mass = (total number of atoms) x (calculated average mass of one atom of Beanium)
QUESTIONS 1. There are 125 navy beans, 56 pinto beans and 144 black-eyed peas in a container. Find the percentage of each of the beans in the container.
2. Suppose your chemistry grade is broken down so that 60% of it is based on exams, 20% on lab reports and 20% on homework. Find your average mark based upon these individual scores: Exams: 78, Labs: 85, Homework: 91
3. There are three isotopes of Neon: Ne 20, Ne 21 and Ne 22. The percentage (relative abundance) of Ne 20 is 90.92%, Ne 21 is 0.257% and Ne 22 is 8.82%. Calculate the average atomic mass for neon, expected to be found on the periodic table. Compare your calculated result to the accepted value for neon.
4. Compare the measured total mass of the sample with the calculated total mass. Discuss why or why not this is the case.
Isotopes – Average Atomic Mass 1. Calculate the average atomic mass of lithium if the percentage (relative abundance) of each isotope is: Li6 - 7.4%, Li7 - 92.6%
2. Calculate the average atomic mass of an atom which has two isotopes. One isotope has a mass of 235 amu and is 0.7% abundant while the other isotope has a mass of 233 amu.
3. Calculate the average atomic mass of an element given that the percentage is 92.3%, 4.70% and 3.00% for isotopic masses of 28 amu, 29 amu and 30 amu respectively. Identify the element.
Isotopes – Average Atomic Mass 4. Chromium has four isotopes. The atomic masses and percentages of these isotopes are listed below: Mass 50 52 53 54
Percentage (relative abundance) 4.31% 83.76% 9.55% 2.38%
Calculate the average atomic mass of chromium.
5. Naturally occurring silicon consists of three isotopes as follows: 92.23% 4.67% 3.13%
Si28 Si29 Si30
Calculate the average atomic mass of silicon.
6. Silver has two isotopes Ag109 (48%) and Ag108 (52%), what is the average atomic mass for silver?
Isotopes – Relative Abundance 1. Iridium has two isotopes with masses of 191 amu and 193 amu and its average atomic mass is 192.2 amu. Calculate the percentage of each of these isotopes.
2. Calculate the percentages of two isotopes of mass 20 amu and 22 amu if the average atomic mass of the element is 20.18 amu.
3. A chemist is given an unknown element A which has an average atomic mass of 210.197 amu. She finds that the element A has only 2 isotopes A 210 and A 212 . What is the percentage of the two isotopes?
Isotopes – Relative Abundance Trick Question: Magnesium has three isotopes with mass numbers of 24 amu, 25 amu and 26 amu. If the last two are present in equal numbers and the average atomic mass is 24.32 amu, calculate the percentage of each isotope.