Atoms bond together to form compounds. There are three main types of chemical bonds: ionic (transfer of electrons), covalent (sharing of electrons), and metallic (sea of electrons). The type of bond determines the properties of the substance formed.
Ionic bonding
Ionic bonds form between a metal and a non-metal. The metal LOSES electrons to become a positive ion (cation); the non-metal GAINS electrons to become a negative ion (anion). The opposite charges attract. Example: Sodium chloride (NaCl) Na → Na⁺ + e⁻ (sodium loses one electron) Cl + e⁻ → Cl⁻ (chlorine gains one electron) Na⁺ and Cl⁻ attract each other to form NaCl. Properties of ionic compounds: high melting point, conduct electricity when dissolved or molten, form crystals.
Covalent bonding
Covalent bonds form between two non-metals. Atoms SHARE pairs of electrons. Single bond: one shared pair (e.g. H-H in H₂) Double bond: two shared pairs (e.g. O=O in O₂) Triple bond: three shared pairs (e.g. N≡N in N₂) Draw dot-and-cross diagrams to show the shared pairs. Only show the outer shell electrons. Properties of covalent compounds: usually low melting point, do not conduct electricity (no ions), can be gases or liquids at room temperature.
Metallic bonding
In metals, atoms release their outer electrons into a 'sea' of delocalised electrons. The positive metal ions are held together by the attraction to this electron sea. This explains why metals: • Conduct electricity (delocalised electrons carry charge) • Conduct heat (electrons transfer energy) • Are malleable and ductile (layers of ions slide without breaking bonds)
Key points
- Ionic: metal + non-metal, electron TRANSFER
- Covalent: non-metal + non-metal, electron SHARING
- Ionic compounds: high MP, conduct when dissolved
- Covalent compounds: usually low MP, poor conductors
- Metallic bonding: sea of electrons, explains conductivity
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WAEC tip
WAEC frequently asks you to draw dot-and-cross diagrams. Practice NaCl (ionic) and H₂O (covalent) until they're automatic.
Practise this
Draw dot-and-cross diagrams for: (a) NaCl, (b) H₂O, (c) N₂. Label which type of bond each is.
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