1. 11.4 Electron Configurations
And the Periodic Table

2. 11.4 Electron Configurations (p377)
The electron configuration of hydrogen is “1s1”
This means there is one electron in the 1s orbital.

3. 11.4 Electron Configurations
Rule 1: Electrons occupy the lowest orbital energies first. 2p
Energy 2s
Then here 1s
First here

4. 11.4 Electron Configurations
Rule 2: Pauli Exclusion Principle: Two electrons can occupy the same orbital.
They have different “spins” 2p
Energy 2s 1s
One
Two

5. 11.4 Electron Configurations
Rule 3: Electrons will not “pair up” in the same orbital until all energy levels are occupied. 2p
Energy 2s 1s

6. Example: Sodium (Na)
Start by drawing a dashed line for each sub-orbital needed in the correct order. 1s 2s
2px
2py 3s
2pz

7. 11.4 Electron Configurations
Look at your field diagram
The order of the “seats” is the same as the order of orbitals.
Notice the 4th energy level has seats closer than some of the 3rd energy level.
Which orbital fills up first, 4s or 3d?
Yes, 3d.

9. Electron Configuration
Quicker way to write the orbital notation
Example: sodium
Becomes s22s22p63s1 1s 2s
2px
2py 3s
2pz

10. 11.4 Electron Configurations
Examples: Li (Z=3), N (7), O(8) (See book)
Mg can be written as [Ne]3s2
Valence electrons are the electrons in the highest principal energy level of an atom. They are involved in bonding with other atoms.
Nitrogen has electrons in n = 1 and 2. Level 2 is the valence level. 1s22s22p3
Nitrogen has 5 valence electrons.

11. 11.4 Electron Configurations
The core electrons are the inner electrons, and are not involved in bonding.
Question: What elements have the same number of valence electrons as N?
Where are they on the periodic table?
Elements with the same number of valence electrons have similar chemical properties.

12. Number one less than row number Number two less than row number
B. Electron Configurations and the Periodic Table.
Helium actually part of s-block 1 2
s-block 3
p-block
d-block
Number one less than row number 4 5 6 7
f-block
Number two less than row number

13. Example: Germanium (Ge)
Do the orbital notation 1s 2s 2p 2p 2p 3s 3p 3p 3p 4s 3d 3d 3d 3d 3d 4p 4p 4p

14. 11.4 C. Atomic Properties and the Periodic Table
Representative Elements - groups 1A-8A
Ionization – ionization is when an atom loses an electron.
Remember: ______________ lose electrons.
_______________ gain electrons.
Going down a group, atoms are more likely to lose an electron. Cs is more likely to lose an electron than Li.
Metals
Nonmetals

15. 11.4 C. Atomic Properties and the Periodic Table
Atomic size – decreases going up and right.
Decreases going up because electrons are closer at lower principal energy levels.
Decreases going right because the + charge in the nucleus is stronger.

16. Atomic Size
Size generally decreases
Size generally decreases

17. 11.4 C. Atomic Properties and the Periodic Table
Ionization energy - the energy required to remove an electron from an atom in the gas phase.
increases up a group
increases to the right

18. Ionization Energy
Increases
increases

19. Checkpoint Which element has a larger atomic size?
Sulfur or chlorine?
Answer: Sulfur
Which element has the larger ionization energy?
Sodium or potassium?
Answer: Sodium