### Oxidation States and Criss Cross Method

```Topic: Oxidation States and Criss Cross
Method
• Do Now: Ionic, Covalent or Metallic
1.
2.
3.
4.
5.
Mg
MgO
NaCl
CO2
H2O
1.Metallic
2.Ionic
3.Ionic
4.Covalent
5.Covalent
Ionic bond is a bond between:
positive ion and negative ion
• Metals: lose valence electrons
–form cation (+ ion)
• Nonmetals: gain electrons
–form anion (- ion)
• Metals lose their valence electrons and
nonmetals gain
IONIC BONDING
• Ionic compounds are electrically neutral
overall
1 Ca = +2 x 1 = +2
2 Cl = -1 x 2 = -2
2 K = +1 x 2 = +2
1 S = -2 x 1 = -2
2 Cr = +3 x 2 = +6
3 O = -2 x 3 = -6
Assigning Oxidation States
• You can look at your periodic table. It’s listed
in the topic right corner.
• What do you do if there is more then one?!
What to do if more then 1 oxidation
state
• V2S5
–Nonmetal = top number
–So S would be -2
+5
-2
–V2S5
____
+5 x 2 = +10
-2 x 5 = -10
• Then determine the oxidation state of the
metal that will give you the same number
but positive
You try…
+2 O= ____
-2
• FeO Fe=____
-2
+3 O= ____
• Fe2O3 Fe=____
Criss-Cross Method
Mg+2 and Cl-1
Crisscross and Drop
Mg1Cl2
but if subscript is 1, forget it!
MgCl2
means 1 Mg+2 and 2 Cl-1
NOTE: The formula has to be in the
simplest whole number ratio (this is
called the empirical formular
Be2O2 = BeO
Al3N3 = AlN
Try a few formulas:
•
•
•
•
•
•
•
Ca+2 + Cl-1
Na+1 + O-2
Cs+1 + S-2
Al+3 + Cl-1
Al+3 + Se-2
Mg+2 + F-1
Ca+2 + S-2
CaCl2
Na2O
Cs2S
AlCl3
Al2Se3
MgF2
CaS
```