Ionic bonding

Ionic bonding occurs when metal atoms transfer electrons to non-metal atoms.

Metals

• Metals lose their outer-shell electrons to form positively charged ions (cations), achieving a stable, full outer shell (noble gas configuration)

Non-metals

• Non-metals gain electrons to form negatively charged ions (anions), achieving a stable, full outer shell (noble gas configuration)

Electron Transfer by Group Number

• Group 1 metals lose 1 electron
• Group 2 metals lose 2 electrons
• Group 3 metals lose 3 electrons
• Group 7 non-metals gain 1 electron
• Group 6 non-metals gain 2 electrons
• Group 5 non-metals gain 3 electrons

Transition Metal Ion Charges

Transition metal ion charges such as Cu²⁺, Fe²⁺, Fe³⁺, and Zn²⁺ must be memorised, as they cannot be predicted from the group number.

Polyatomic Ions

• Hydroxide, OH⁻
• Ammonium, NH₄⁺
• Carbonate, CO₃²⁻
• Nitrate, NO₃⁻
• Sulfate, SO₄²⁻

Ionic formulae are written by balancing the ion charges so that the overall charge is zero, using brackets around a polyatomic ion when more than one of it is needed.

Key Definition An ionic bond is the strong electrostatic attraction between oppositely charged ions.

Giant Ionic Lattice

• Each ion is surrounded by ions of the opposite charge, with the electrostatic attractions extending in all directions throughout the lattice
• Ionic compounds have high melting and boiling points, because a large amount of energy is required to overcome the many strong electrostatic attractions between the ions
• Ionic compounds do not conduct electricity as solids, because the ions are fixed in fixed positions and cannot move
• When molten or dissolved in water, the ions become free to move and can carry charge, so the compound conducts electricity

Dot-and-cross Diagrams

Dot-and-cross diagrams illustrate the electron transfer by using a different symbol (a dot or a cross) for the electrons from each atom, with only the outer-shell electrons shown.