Ionic Bonding

- Ionic compounds form when metals combine with nonmetallic elements.
Charges Gained on Ions:

Group	Charge
Group 1	1+
Group 2	2+
Group 3	3+
Group 5	3-
Group 6	2-
Group 7	1-
Cations formed by metals	Anions formed by non-metals

- By losing/gaining electrons on the outer shell, they end up with full/stable shells.

- Groups 1, 2, and 3 lose electrons: Metals
- Groups 5, 6, and 7 gain electrons: Nonmetals

Dot and Cross Diagrams:

Eg. sodium chloride (NaCl)

- Na⁺ is positive, as it has one more proton than an electron now.
- Cl⁻ is negative, as it has one more electron than a proton.
- When electrons transfer, they must remain unchanged.

Eg. Aluminium Oxide (Al₂O₃)

 

- We need two aluminium ions and three oxide ions to cancel out the charges.

- The positive and negative ions attract each other in the compound because opposite charges attract, causing an ionic bond.
- Ionic crystals are made up of a regular alternating pattern of cations and anions, which are held together by strong electrostatic forces of attraction. This pattern requires a lot of energy to break, which is why they have high melting points. They are found in a giant ionic lattice.
- In a giant ionic lattice, there's also a regular alternating pattern of cations and anions held together by strong electrostatic forces of attraction.

Formulae

Ions to Memorise:

Ion	Formula
Nitrate	NO3-
Ammonium	NH4+
Sulfate	SO42-
Hydroxide	OH-
Carbonate	CO32-
Zinc	Zn2+
Copper (II)	Cu2+
Silver	Ag+
Iron (II)	Fe2+
Iron (III)	Fe3+
Lead	Pb2+

Formula of Ionic Compounds:

- The ion charges must cancel out in the compound.

E.g., Magnesium Chloride
Mg²⁺ Cl^- → need 2 Cl to cancel out charge
MgCl₂

E.g., Sodium Carbonate
Na⁺ CO₃^2-
Na₂CO₃

E.g., Ammonium Nitride
NH₄⁺ N^3-
(NH₄)₃N put in brackets for extra charge

E.g., Magnesium Hydroxide
Mg²⁺ OH^-
Mg(OH)₂

E.g., Calcium Sulfate
Ca²⁺ SO₄^2- charge is even/same, so no need to be in braces.
CaSO₄

- Only the electron number can change when atoms become ions.