1. Unit 2 Atomic Structure Atomic Theory What is a Theory?
A set of statements or principles devised to Explain a group of facts or phenomena.
Describe the Discontinuous Theory of Matter.
Matter is made of tiny particles that cannot be cut any smaller. 2,500 years ago, Greek for not-cut is “a-tom”  atoms (Democritus).
What Theory of Matter was commonly accepted for most of the last 2,000 years?
Four Elements: Earth, Air, Fire, and Water and Four Qualities. Matter can be Continuously Divided into smaller parts.
How did the current Atomic Theory evolve?
The modern model of the atom evolved over a long period of time through the work of many Scientists and many, many Experiments.
What does this data indicate?
1. Atoms of different elements may have ___________ ___________.
different masses
Conserved
2. Mass is ____________________ in a chemical change.
= = =
3. Different Atoms combine in ___________ _________ to form Compounds.
Definite Ratios

2. Mass is Conserved in a Chemical Change
The mass of tin usually increase as it reacts in air to form tin oxide What might this experiment show?
Matter (Mass) is Neither Created nor Destroyed in a Chemical Change.
A Chemical Change is a Rearrangement of the original Atoms.
The glass dome seemed to be “stuck” like a suction cup after the reaction. WHY?
The air inside produces a lower pressure without the Oxygen molecules. Outside air pressure has not changed and is higher by comparison.
Link to Dalton’s Playhouse Interactive.

3. Atoms Have an Electrical Nature
What did Thomson discover using a cathode ray tube?
Atoms contain “Electrons”: Negatively Charged Sub-Atomic Particles.
What Model of the Atom Resulted from such discoveries?
The “Plum Pudding” model resulted.

4. The Nuclear Atom Describe Rutherford’s Gold Foil Experiment.
Most radioactive Alpha particles go straight through thin Gold Foil.
A few (+) Alpha particles are deflected and very few bounce back.
What did Rutherford infer about the structure of Atoms?
1. Atoms are Mostly Empty Space.
2. Atoms have a very dense, very tiny, and positively charged Nucleus.

5. The Nature of Light
Does Light behave as a Particle or as Electric and Magnetic Waves?
Light shows Both types of Behaviors!
“Particle” is called a Photon.
What is Electromagnetic Radiation?
Waves of Electric and Magnetic Forces that Radiate at the speed of light.
Describe the relationship between the Wavelength, Frequency, and Energy of Electromagnetic Radiation?
Shorter Waves have a Higher Frequency and a Higher Energy.
Link to Waves Go to: Radio Waves Microwaves Photoelectric Effect
Higher Energy
Link to Electricity Go to: Balloons Generator
What is the difference between blue light and red light?
Blue light has a shorter wavelength, higher frequency and higher energy.

6. Link to Spectra (Click Emission)
The Bohr Model
How does the Emission Spectra produced by atoms relate to atomic structure?
Spectroscopes show that Atoms produce light with Distinct Amounts of Energy.
Each Electron in an Atom has a Distinct Amount of Energy.
How do atoms produce light?
1. Electrons can Absorb Energy and change to a Higher Energy State (Excited State).
Link to Model
2. When an excited electron Returns to a Lower Energy State it emits a “Quanta” of light with specific energy and specific color.
Link to Spectra (Click Emission)

7. The Wave-Mechanical Model
How does the Wave-Mechanical Model describe the behavior and the location of Electrons in an atom?
Electrons have a wave character and are located in Orbitals.
Orbitals (electron clouds) are regions of probable location of electrons.
How can one orbital hold up to two electrons?
Electrons with Opposite Spins create Opposite Magnetic Forces = Attraction.

8. Sub-Atomic Particles
Compare the three types of sub-atomic particles...
In terms of charge,
Protons are positive (+1), Electrons are equally negative (-1), and Neutrons are neutral.
In terms of location,
Protons and Neutrons are in the nucleus while Electrons are in Orbitals outside the nucleus.
In terms of mass,
Protons and Neutrons have similar masses of approximately one atomic mass unit (amu) while Electrons have much, much less mass (1/1,849 amu) often considered nearly zero or zero.
What does the Atomic Number of an Element indicate?
1. Atomic Number indicates the Number of Protons in an Atom.
2. Atomic Number indicates the Nuclear Charge (+).
3. The Atomic Number is Different for each Element.
What does the Mass Number of an atom indicate?
Mass Number is the Sum of Protons and Neutrons in the Nucleus.
How are Atoms Different from Ions?
Atoms are Always Neutral: # Protons = # Electrons.
Ions are Charged. # Protons and # Electrons are NOT Equal.

9. Isotopes and Atomic Mass
What are Isotopes?
Isotopes are Atoms of the Same Element, but with Different Masses due to Different…
numbers of neutrons.
Ex. How is Carbon-12 different from Carbon-14?
Different Mass Numbers. Both Isotopes have 6 Protons. A C-12 nucleus also has 6 neutrons while a C-14 nucleus has 8 neutrons (6p + 8n = 14 amu) *
*Both Chemically similar, however, C-14 is Radioactive while C-12 is not.
What is the Atomic Mass of an Element? 12
Atomic Number = Number of Protons in the nucleus of every atom of magnesium. Mg
Atomic Mass = Average Mass (amu) of naturally occurring Isotopes of Mg.
Magnesium
What Isotope of Mg is probably most common?
 Mg-24 is probably most common. (Round to nearest whole number)
What are the most common isotopes of Carbon, Nitrogen, Oxygen, Fluorine?
Carbon-12 Nitrogen-14 Oxygen-16 Fluorine-19

10. Determination of Atomic Mass
Given Relative Abundance of Isotopes and Actual Mass* (amu), determine the Atomic Mass of an Element.
* Note: Actual mass of protons and neutrons can vary with different nuclei!! The atomic mass unit (amu) is based on Carbon-12. (1 amu = 1/12 the mass of a C-12 atom)
Ex. Determine the average atomic mass of chlorine.
Chlorine
Isotopes
Natural % Abundance
Mass (amu)
Cl-35
75.77%
34.969
Cl-37
24.23%
36.966
75.77% 
24.23% 
+______
X amu = amu
X amu = amu
Atomic mass = amu
Copper
Isotopes
Natural % Abundance
Mass (amu)
Cu-63
69.2%
62.93
Cu-65
30.8%
64.93
Determine the atomic mass of Copper.
Atomic mass = 63.5 amu

11. Atoms, Ions and Isotopes
Differentiate between Atomic Mass and Mass Number.
Atomic Mass is a Measured* Average Mass of all naturally occurring Isotopes of an element.
* Includes significant figures.
Mass Number is the Sum* of protons and neutrons in specific atom of an element.
*A Counted value: No significant figures Always a Whole Number. Never given in the Periodic Table.
How can one properly represent a specific atom of an element?
A Chemical Symbol is either a single capital letter or a capital and a lower case letter.
How can one give the proper notation to represent a specific isotope? Ex. Carbon-14…..
C C C ?
Protons = At. No.
How can one represent the charge of an ion? Ex. Magnesium with 12 protons and 10 electrons. 2+ Mg
Give the proper notation for a particle containing 8 protons, 9 neutrons, and 10 electrons.
(+8) + (-10) = -2
Sum of protons + neutrons
Link to Build an Atom
178O2-
8 protons = Oxygen

12. Practice With Particles
Complete each item with what can be known Use “?” for what cannot be known.
Isotopic Notation
Number of Protons
Number of Neutrons
Number of Electrons
42He
14__C 13 14 10
3216S 18
23Na

13. Practice With Particles
Complete each item with what can be known Use “?” for what cannot be known.
Isotopic Notation
Number of Protons
Number of Neutrons
Number of Electrons
42He 2
14_6_C 6 8
2713Al3+ 13 14 10
3216S2- 16 18
2311Na+ 11 12

14. Practice With Particles 2
Complete each item with what can be known Use “?” for what cannot be known.
Isotopic Notation
Number of Protons
Number of Neutrons
Number of Electrons 15 7
K + 32 17 36 24 27 22

15. Practice With Particles 2
Complete each item with what can be known Use “?” for what cannot be known.
Isotopic Notation
Number of Protons
Number of Neutrons
Number of Electrons 15 N 7 8 ?
K + 19 18 32
P2- 17
3617Cl
5124Cr2+ 24 27 22

16. Definite Ratios
What seems to be true regarding the Volume of a Gas and the Number of Gas Molecules?
At same Temperature and Pressure, Equal Volumes of Gases contain Equal Number of Gas Molecules.
How does the mass of one Oxygen (O2) balloon compare with the mass of one Hydrogen (H2) balloon?
O2 = amu X 2 atoms/molecule = amu
H2 = amu X 2 atoms/molecule = 2.02 amu
For a Simple Ratio: Set Smaller number equal to one, determine Larger value.
X = 32 x 1 ÷ 2.02 = 15.8 x
mass O2
32.00 amu O2
= __________
O2 Balloon is 15.8 times heavier than H2 Balloon.
2.02 amu H2 1
mass H2

17. Additional mass came from something in the air
Percent Oxygen in Air
What does this experiment demonstrate about the apparent increase in mass of product?
Additional mass came from something in the air
Why did the water rise into the glass jar during the reaction?
Outside Air pressure pushes the water up against the weaker Inside Air pressure until all forces are balanced
What percentage of the original volume of air was taken up by the water after the reaction? Why?
If All the Oxygen in the air reacts, then approximately 21% of the volume will be water. Oxygen gas occupies much, much more volume than Oxygen in solid phase as Tin Oxide