Bonding, structure and the properties of matter

2.1 · Free notes

Ionic, covalent and metallic bonding

Key points

• Ionic bonding occurs between metals and non-metals: electrons are transferred, forming oppositely charged ions held in a giant lattice by strong electrostatic forces.
• Covalent bonding occurs between non-metals: atoms share pairs of electrons, forming simple molecules (e.g. water) or giant covalent structures (e.g. diamond).
• Metallic bonding: metal atoms form a giant lattice of positive ions surrounded by a 'sea' of delocalised electrons, free to move throughout the structure.
• All three bonding types involve strong electrostatic forces of attraction, requiring a lot of energy to overcome, though the resulting structures give very different properties.

In more detail

• Dot and cross for NaCl: sodium (2,8,1) transfers one electron to chlorine (2,8,7), giving Na⁺ [2,8] and Cl⁻ [2,8,8], drawn in square brackets with the charge outside.
• Formulae from charges: Mg²⁺ and Cl⁻ give MgCl₂; Al³⁺ and O²⁻ give Al₂O₃ (charges must cancel: 2 × 3+ = 6+, 3 × 2− = 6−).
• Covalent examples: H₂ (one shared pair), H₂O (two single bonds), O₂ (a double bond), N₂ (a triple bond), CH₄ (four single bonds).
• Limitations of diagrams: dot and cross diagrams do not show 3D shape; ball and stick models wrongly suggest big gaps between atoms.