1. Class Notes-Bohr & New Atomic Model (Chapter 4, Section 1)
Arrangements of Electrons in Atoms
Thursday, October 29th, 2015

2. The Development of a New Atomic Model
Rutherford’s model was incomplete
How were electrons distributed?
What prevents negative electrons from crashing into positive nucleus?
1900s-New Atomic Model (revolutionary)
Relationship between light & electrons

3. How many Electrons Can Fit in Each Energy Level?
Energy level is also called “principal quantum number”
Energy Level = n
n max. # electrons
1 2
2 8
3 18
4 32
5 50
6 72
Max # e = 2n2
Big Question: Why?

4. There are two ways to state the location of an electron…
Quantum numbers – the location of a specific electron
Electron configurations – the addresses of every electron in an atom (read the periodic table like a book!)

5. Quantum numbers
Principle quantum number (n) = identifies the energy level of the electron
Angular momentum quantum number (l) = identifies the sublevel
Spin quantum number = identifies the orientation in the pair

7. Properties of Light Before 1900s-thought light behaved as a wave
During 1900s-also has particle characteristics
Electromagnetic Radiation

9. Electromagnetic Spectrum
High Freq Low Freq
High E Low E

10. Wavelength & Frequency
Speed of light = 3.00 x 108 m/s c
Wavelength = distance between waves 
Frequency = # waves that pass point in 
given time
c =  
as  increases,  decreases
as  increases,  decreases
(slinky analogy)

12. Emission of electrons from a metal when light shines on metal
Light of minimum frequency was required to eject electron from metal
Problem-wave theory of light predicted light of any frequency could eject electron
Photoelectric Effect

13. Is Light a Particle?
Max Planck-hot objects emit energy not as waves, but in packets called “quanta”
“quantum”-minimum energy that can be gained or lost by an atom
E = h
E = energy
h = Planck’s constant (6.626 x Js)
 = frequency (in s-1)

14. Light as a Wave & Particle
Einstein’s radical idea!
Dual wave-particle nature of light
Called particles of light “photons” (no mass)
Explained photoelectric effect (photon must have minimum energy)
Light is absorbed only in whole numbers of photons
Light as a Wave & Particle

16. Emission Spectra White light -continuous spectrum Hydrogen atoms
-line-emission spectrum
Big Question
-Why did hydrogen
atoms only give off
specific frequency
(colors) of light?

17. The “Fingerprints” of Atoms

18. Atomic Spectra
The atom is quantized, i.e. only certain energies are allowed.

19. Neils Bohr Solved the Mystery
Electron circled nucleus in “orbit” of fixed energy
Absorption-electrons can “hop” from ground state to excited state
Emission-when electrons “fall” from excited state to ground state
Energy difference corresponds to hydrogen’s spectral lines
Ladder analogy

21. Remaining Mystery Bohr’s model only explained hydrogen atom
What about other elements with more than one electron?