1. Modern Atomic Theory
Physical Science

2. State Standards
CLE.3202.Inq.1 – Recognize that science is a progressive endeavor that reevaluates and extends what is already accepted

3. Review of First Models Democritus : Used atomos to describe matter
No experiments, just observation with naked eye
John Dalton : Experiments to combine gases
Developed Law of Definite Proportions
J.J. Thompson : Cathode-Ray Tube
Discovered electrons / Plum Pudding model
Earnest Rutherford : Gold Foil experiment
Discovered nucleus ( protons ) / Modern view
Electrons orbit nucleus in definite paths ( planets/sun )

4. What Do We Know Now?
Model ( conceptual view ) of the atom has changed significantly since Rutherford’s model
Now know that electrons are found only in ( at ) certain energy levels – not between levels
Electrons act like waves
Exact locations of electrons cannot be determined

5. Electron Energy Levels
In 1913, Niels Bohr suggested that electrons can reside only at certain energy levels
Electrons must gain energy to move up
Electrons must lose energy to move down
ELEVATOR MODEL

6. Electrons – Particles and Waves
By 1925, Bohr’s model no longer explained all aspects of electron behavior
Electrons act like particles but they also act like waves too
Wave-Particle duality
Smaller the particle, the more it acts like a wave
Concept of electrons redefined
Imagine a wave vibrating on a string ( demo? )

7. Wave-Particle Duality
In 1923, Louis de Broglie ( a French physicist ) made a hypothesis that led to a statement of the WAVE-PARTICLE DUALITY of nature.
It included the present theory of atomic structure
De Broglie used research by Albert Einsten and Max Planck to develop an equation relating mass and velocity of a particle to its wavelength

8. Electron Energy Levels
Number of levels filled depends on electrons
specific to an element
Valence electrons are those on the outer level
Valence e- determine properties ( reactivity )
Energy Level 1 holds 2 e-
Energy Level 2 holds 8 e-
NUCLEUS
Energy Level 3 holds 18 e-
Energy Level 4 holds 32 e-

9. Electron Energy Levels of Li
Lithium as example
3 electrons in Li
1 Valence electrons
In level that holds 8
Energy Level 1 holds 2 e-
Energy Level 2 holds 1 e-
NUCLEUS
Energy Level 3 holds 0 e-
Energy Level 4 holds 0 e-

10. Location of Electrons Imagine the moving propeller of an airplane
Now determine the location of any blade at any time
How would you do this?
Exact position of electrons also hard to calculate
Moving very fast always ( never stop or slow down )
Orbitals ( regions where electrons might be ) are thus used to describe an approximate location
Different orbital SHAPE for different orbital types

11. Bellwork – 02/21/17
What are the orbitals named [ where electrons may be found ]?

12. Electron Orbitals Four orbitals : s, p, d, and f
d and f orbitals are more complex
5 possible d orbitals ( holds up to 10 electrons total )
7 possible f orbitals ( holds up to 14 electrons total )

13. Energy Levels and Orbitals
1st energy level has only s orbital
2nd energy level has s and p orbitals
3rd energy level has s, p, and d orbitals
Energy Level 1 holds 2 e-
s orbital ONLY
Energy Level 2 holds 8 e-
s and p orbitals
Energy Level 3 holds 18 e-
s, p and d orbitals
Energy Level 4 holds 32 e-
s, p, d, and f orbitals

14. Energy Levels and Orbitals of Li
1st energy level has only s orbital
2 electrons
2nd energy level has s and p orbitals
1 electron
Energy Level 1 holds 2 e-
s orbital ONLY
Energy Level 2 holds 1 e-
s and p orbitals
Only 2s orbital used
Energy Level 3 holds 0 e-
s, p and d orbitals
Energy Level 4 holds 0 e-
s, p, d, and f orbitals

15. Energy Levels and Orbitals
Each energy level has a unique orbital layout
Orbitals in each energy level decide total number of electrons that can be at each energy level
Example – the 2nd energy level holds 8 e-
has an s ( holds 2 e- ) and a p ( holds 6 e- )orbital
Energy Level
Number of Orbitals by Type ( for each energy level )
Total
Orbitals
2 e- per orbital
Number e- spots s p d f
x2 for all 1
1 = 1 2 3
1 + 3 = 4 8 5
= 9 18 4 7
= 16 32

16. Electron Transitions
Electron locations limited to certain energy levels
How do electrons move between levels?
When an atom gains or loses energy
Ground state – lowest energy level of electron
At normal (room) temps, electrons at ground state
Excited state – when electron has gained energy

17. Atoms Emit & Absorb Light
Photons are absorbed by electrons to move it from ground to an excited state
Released when they go down the elevator
Photon – a particle of light
Photons have different energies
Elevator model – energy of emitted photon depends on how many levels are crossed

18. Atoms Emit & Absorb Light
Energy of photon is related to wavelength of light
High-energy photons have short wavelengths
Low-energy photons have long wavelengths
Wavelengths emitted depend on element
Since each element has a unique structure
Atomic “fingerprint”
Neon signs : Neon ( Ne ) gas produces red light
other gases emit different colors of light
Color depends on wavelength of light emitted