1. TOPIC: Electrons in Atoms
Ground/Excited States
Do Now: Draw Bohr’s Model for Argon

3. Memory Jogger Cathode Ray Tubes & Discovery of Electrons
Movie of cathode ray tube

4. Thomson’s Plum-Pudding Model
The positive charge is evenly smeared out.
The negative charge is in bits – like chips.
source

5. Rutherford’s Experiment - 1911
source

6. Problems with the Rutherford Model
Why don’t electrons crash into nucleus?
How are electrons arranged?
Why do different elements exhibit different chemical behavior?

7. Bohr Model
Bohr - electrons in atom can have only specific amounts of energy NEW idea!
Each specific energy is associated with specific orbit
--electrons are restricted to these orbits

8. Bohr assigned quantum number (n) to each orbit the smallest orbit (n= 1) is closest to nucleus has lowest energy larger the orbit, more energy it has
n=3
n=2
Lowest energy
(most stable)
Highest energy
(least stable)
n=1

9. Max Capacity of Bohr Orbits
2n2 n 32 4 18 3 8 2 1
Max # of Electrons
Orbit

10. energy levels get closer together the farther away they are from nucleus
Larger orbits can hold more electrons

11. Electron Transitions EXCITED STATE:
If electron gains (absorbs) specific amount of energy it can be excited to higher energy level (farther from nucleus – less stable)
Endothermic process
GROUND STATE:
Energy released when electron:
drops to lower orbit (closer to nucleus – more stable)
Exothermic process

12. Ground State vs. Excited State
Lowest energy state of atom
electrons in lowest possible energy levels
Configurations in Reference Tables are ground state
Excited state:
Many possible excited states for each atom
One or more electrons excited to higher energy level

14. Ground State comes from the reference table
Ar = 2-8-8
Total number of electrons = 18
Total number of protons = 18
Atomic Number = 18

15. Excited State comes from the reference table
Total number of electrons = 18
Total number of protons = 18
Atomic Number = 18
Look on the periodic table for the atomic number 18, what is the ground state electron configuration

16. Which principal energy level of an atom contains electron with the lowest energy?
B) n=2
C) n=3
D) n=4

17. What is total # of occupied principal energy levels in atom of neon in ground state?
B) 2
C) 3
D) 4

18. Which atom in ground state has five electrons in its outer level and 10 electrons in its kernel?
A) C
B) Cl
C) Si
D) P
Kernel electrons = inner electrons

19. Which electron configuration represents atom in excited state?
B) 2-8-1
C) 2-8
D) 2-7-1

20. Which electron configuration represents atom of Li in an excited state?
B) 2-0-1
C) 2-1
D) 2-2