1. Getting from the orbitals to the elements
All elements have the same set
Atomic number dictates how many are filled – how many electrons are added
Filling orbitals follows a fixed pattern: lowest energy ones first
Questions:
What is the order of the energies?
And how many electrons per orbital?

2. Orbital energy levels and order of filling

3. Electrons share orbitals (only two allowed) – a consequence of spin

4. Capacities of the sublevels – 2 x number of orbitals
Number of members
Electron capacity
1s, 2s etc 1 2
2p, 3p etc 3 6
3d, 4d etc 5 10
4f, 5f etc 7 14

5. Add electrons to the orbitals – lowest first2p 3d 3p 4p 4s 3s 2s 1s
H(z = 1)

6. Fill lowest orbital 2p 3d 3p 4p 4s 3s 2s 1s
He(z = 2)

7. Begin next orbital 2p 3d 3p 4p 4s 3s 2s 1s
Li(z = 3)

8. Fill 2s 2p 3d 3p 4p 4s 3s 2s 1s
Be(z = 4)

9. Begin filling 2p 2p 3d 3p 4p 4s 3s 2s 1s
B(z = 5)

10. Electrons don’t like to pair
C(z = 6)

11. 2p 3d 3p 4p 4s 3s 2s 1s
N(z = 7)

12. 2p 3d 3p 4p 4s 3s 2s 1s
O(z = 8)

13. 2p 3d 3p 4p 4s 3s 2s 1s
F(z = 9)

14. Filled 2p – neon (unreactive)4s 3s 2s 1s
Ne(z = 10)

15. 4s is lower in energy than 3d
Next electron enters 4s not 3d 2p 3d 3p 4p 4s 3s 2s 1s
K(z = 19)

16. But 3d is lower in energy than 4p
Next electron enters 3d not 4p 2p 3d 3p 4p 4s 3s 2s 1s
Sc(z = 21)

17. Follow the red brick road: fill orbitals in correct order
Practice makes perfect

18. Electronic configurations
Provides a complete description of all electrons in atom according to orbital occupancy
Consider Al: atomic number 13
Has thirteen electrons
Orbitals occupied in order:
1s22s22p63s23p1
Occupancy
“Sublevel” quantum number
Principal quantum number

19. Abbreviated configurations
For large elements, the full configuration becomes unwieldy
Substitute the largest noble gas for all the filled rows, but not the unfilled rows
Na is 1s22s22p63s1
Ne is 1s22s22p6
Na is [Ne]3s1
Leads into concept of valence and core electrons

20. Shells
The orbitals with the same Principal Quantum number (1,2,3 etc) are grouped into shells (levels)
Filled shells have special significance
Filled shell 1
Filled shell 1
Unfilled shell 2
Filled shell 2

21. Shells
A shell (level) contains all the orbitals with the same principal quantum number
Filling shell corresponds to filling entire period in table (2, 8 or 18 electrons)
Filled shells are in the core – they do not participate in the chemistry

22. # of valence electrons = group number
The electrons in the unfilled shell are called the valence electrons
This unfilled shell is the valence shell
The valence electrons are involved in bonding
For any element:
# of valence electrons = group number
Quantum number of shell (n) = period number

23. Shape of the periodic table explained by orbital picture
6 groups
2 groups
10 groups
14 groups