1. 8.5 – Valence Electrons 1s2 2s22p6 3s23p6 4s1
When atoms undergo a chemical reaction, only the outermost e- are involved (furthest from nucleus and highest in energy  valence electrons

2. Electron Configuration
Valence electrons are the ones in the s and p subshells beyond the noble gas core, and partially filled d and f subshells
If all subshells are completely full in a atom (i.e. noble gas) then there are no valence electrons
Atom
Electron Configuration
# Valence e- Al Ga Pb Xe
[Ne] 3s23p1 3
[Ar] 4s23d104p1 3
[Xe] 6s24f145d106p2 4
[Kr] 5s24d105p6
0 or 8

3. Can you see a pattern for counting valence electrons on the periodic table?1 2 3 4 5 6 7
0 or 8
varied

4. 8.6 – Electron Configuration of Ions
1s22s22p4
What’s changed from O to O2-?
If you had to guess where to stick the two electrons, where would they go?
O2-: ??

5. 1s22s22p4 + 2e-  1s22s22p6 1s22s22p63s23p4 + 2e-  1s22s22p63s23p6
For negative ions, add the extra electron(s) where you left off in the neutral atom
Example: Write the electron configuration for the following negative ions:
a) O2-
1s22s22p4
+ 2e- 
1s22s22p6
b) S2-
1s22s22p63s23p4
+ 2e- 
1s22s22p63s23p6
c) Br-
[Ar]4s23d104p5
+ 1e- 
[Ar]4s23d104p6

6. Sn: Sn2+: ?? 1s22s22p63s23p64s23d104p65s24d105p2 highest n p s d
For positive ions,
Electrons in subshells with the _______________ value and highest energy are moved first
Electrons are removed from the ____ -subshell first, then ____, and then _____-subshells
highest n p s d
Sn:
1s22s22p63s23p64s23d104p65s24d105p2
What has changed between Sn and Sn2+?
Before I ask you if you had to guess where the electrons will be removed from, where are they most definitely not removed from? Which subshells are not involved in creating a positive ion?
Sn2+: ??

7. highest n p s d [Kr]5s24d105p2 - 2e-  [Kr]5s24d10 [Kr]5s24d105p2
For positive ions,
Electrons in subshells with the _______________ value and highest energy are moved first
Electrons are removed from the ____ -subshell first, then ____, and then _____-subshells
highest n p s d
a) Sn2+
[Kr]5s24d105p2
- 2e- 
[Kr]5s24d10
b) Sn4+
What has changed between Sn and Sn2+?
Before I ask you if you had to guess where the electrons will be removed from, where are they most definitely not removed from? Which subshells are not involved in creating a positive ion?
[Kr]5s24d105p2
- 4e- 
[Kr]4d10
c) V2+
[Ar]4s23d3
- 2e- 
[Ar]3d3

8. noble gas isoelectronic Ne Ar Kr
Example: Write the electron configuration for the following ions:
Neutral Atom
Ion
O2-
S2-
Br-
Sn2+
Sn4+
V2+
1s22s22p4
1s22s22p63s23p4
[Ar]4s23d104p5
[Kr]5s24d105p2
[Ar]4s23d3
+ 2e- →
+ e →
- 2e →
- 4e →
1s22s22p6
1s22s22p63s23p6
[Ar]4s23d104p6
[Kr]5s24d10
[Kr]4d10
[Ar]3d3 Ne Ar Kr
When an atom becomes an ion, its electron configuration sometimes becomes the same as the configuration for the nearest ___________________. When two atoms have the same electron configuration, they are said to be _____________________.
noble gas
isoelectronic

10. Practice: Which of the following is isoelectronic with krypton when ionized?
Cl Zn Br Ca Sr Se I

11. Consider this: If two atoms have the same electronic configuration, are they the same element?
NO!!! It is the #p that determines the element.