1. Electron Configuration: Ions
Valence Electrons

2. Electron Configuration - Cations
Cations – atoms that lose electrons - metals
Electron Configuration:
Magnesium – 12 electrons in its neutral state
1s22s22p63s2
Magnesium ion
Loses 2 electrons
New configuration: 1s22s22p6
Notice that the electron configuration is the same as the noble gas Neon
This indicates that by giving 2 electrons away, it obtains an outer octet (stable valence configuration!)

3. Electron Configuration - Anions
Anions – gain electrons – non-metals
Electron Configuration:
Chlorine – 17 electrons in its neutral state
1s22s22p63s23p5
Chlorine ion
Gains 1 electron
New configuration: 1s22s22p63s23p6
Notice that the electron configuration is the same as the noble gas Argon
This indicates that by gaining 1 electron, it obtains an outer octet (stable valence configuration!)

4. Electron Configuration
Both ions obtain a noble gas configuration
This makes the ion and the noble gas isoelectronic
Isoelectronic: when two elements and/or ions have the same electronic configurations with one another
They tend to have similar chemical properties.

5. Isoelectric Examples Li+1 1s2 He 1s2 S-2 1s2 2s2 2p6 3s2 3p6
Ar 1s2 2s2 2p6 3s2 3p6 

6. Valence Electrons
Valence electrons are the outer-most electrons in an atom
For main group elements (Groups 1, 2, 13, 14, 15, 16, 17, 18) they are the highest level s and p electrons
Example:
Chlorine
1s2 2s2 2p6 3s2 3p The 3s and 3p electrons are valence e-

7. Valence Electrons
The d orbital electrons of the transition elements can also be valence electrons, but they are complicated so we will not study them
However, this is what gives transition elements multiple oxidation states
Example:
Manganese: [Ar] 4s23d5 (neutral atom)
Possible valence electron configs: 2 to 7!