1. IONICIONIC
COMPOUNDCOMPOUND
FORMATIONFORMATION
5.25.2

2. IONSIONS
• Octet rule:
– all elements want 8 valence e-.
• Cations = positive
• Anions = negative, “ide”

3. Opposites AttractOpposites Attract
• Because cations are + and anions are –
they attract each other.
• This attraction forms Ionic Bonds.

4. Ionic BondsIonic Bonds
• Ionic bonds are very strong.
• Ionic Bonds are electrically neutral.
– The charges cancel each other out.
– You have to have the same number of + & -
• Ionic bonds form salts.
– Examples:
NaCl KCl CaI2 MgF2

5. Monatomic or Polyatmoic?Monatomic or Polyatmoic?
• MONATOMIC:
1 atom per ion
• Na+1
• Cl-1
• O-2
• Al+3
• POLYATOMIC:
More than one
atom per ion
• NH4
+1
• SO4
-2
• OH-1

6. Polyatomic IonsPolyatomic Ions
NH4
+1
All of the atoms in the
ion act like ONE
atom.
The nitrogen and
four hydrogens
are like one atom
with a +1 charge.

7. Writing FormulasWriting Formulas
• To write a formula, you combine the
fewest positive ions and negative ions to
make the total charge of

8. EXAMPLESEXAMPLES

9. COMBINE sodium and chlorineCOMBINE sodium and chlorine
Na+1
Cl-1
To combine, we must make the charges = zero
NaClTo name: use the names of the ions
Sodium chlorideSodium chloride

10. COMBINE calcium and bromineCOMBINE calcium and bromine
Ca+2 Br-1
We will need 2 bromine ions to match the +2 of calcium
Ca
Calcium bromideCalcium bromide
Br2

11. COMBINE magnesium and nitrogenCOMBINE magnesium and nitrogen
Mg+2 N-3
Can use least common denominator.
Mg3 N2

12. COMBINE magnesium and nitrogenCOMBINE magnesium and nitrogen
Mg+2 N-3
Mg3N2
Flip flop the charges and turn them into subscripts.

13. Ion formation shortcutsIon formation shortcuts
• If charges are the same number drop
charges and put symbols together.
– The charges cancel out and become ZERO.
• If charges are different numbers criss-
cross the charge numbers and make a
subscript on other ion.

14. Polyatomics???Polyatomics???
K+1
SO4
-2
Remember, in a Polyatomic ion all the atoms act as one,
even the subscripts. If they are already there, they
stay there!
K2SO4
COMBINE potassium and sulfate

15. COMBINE aluminum and sulfateCOMBINE aluminum and sulfate
Al+3 SO4
-2
Al2 SO4 3
( )
How do we separate the subscripts so they look separate?

16. Practice problemsPractice problems
1. Ammonium and chlorine
2. Aluminum and selenate
3. Lead II and bicarbonate
4. Mercury I and phosphate

17. answers
1. NH4Cl Ammonium chloride
2. Al2(SeO4)3 Aluminum selenate
3. Pb(HCO3)2 Lead II bicarbonate
4. (Hg2)3(PO4)2 Mercury I phosphate