Ionic, Covalent and Metallic Bonding
Ionic Bonding
When metals react with non-metals, electrons are transferred from the metal atom to the non-metal atom. The metal atom loses electrons to form a positive ion (cation), and the non-metal atom gains electrons to form a negative ion (anion). Both ions then have full outer electron shells and are stable.
The strong electrostatic attraction between the oppositely charged ions is called an ionic bond. For example, in sodium chloride (NaCl), sodium loses one electron to become \(Na^+\) and chlorine gains one electron to become \(Cl^-\).
Ionic bonding: metal atoms lose electrons (form positive ions) and non-metal atoms gain electrons (form negative ions). The ions are held together by strong electrostatic attraction in a giant ionic lattice.
Covalent Bonding
When non-metals bond with other non-metals, they share pairs of electrons. This is called a covalent bond. Each shared pair of electrons counts as one bond. Examples include:
- \(H_2\) — a single covalent bond (one shared pair).
- \(O_2\) — a double covalent bond (two shared pairs: \(O=O\)).
- \(N_2\) — a triple covalent bond (three shared pairs: \(N \equiv N\)).
- \(H_2O\) — two single covalent bonds.
- \(CH_4\) — four single covalent bonds.
You need to draw dot-and-cross diagrams showing how electrons are shared or transferred. For ionic bonding, show the transfer of electrons and the charges on the resulting ions. For covalent bonding, show the shared pairs of electrons in the overlap between atoms. Only show outer shell electrons. Use dots for one atom and crosses for the other.
Metallic Bonding
In metals, the outer electrons are delocalised — they leave their atoms and form a “sea” of electrons that can move freely through the structure. The metallic bond is the strong electrostatic attraction between the positive metal ions and this sea of delocalised electrons.
Metallic bonding: positive metal ions surrounded by a sea of delocalised electrons. This explains why metals conduct electricity (delocalised electrons carry charge) and are malleable (layers of ions can slide over each other).
Ionic: transfer of electrons, metal + non-metal, forms a giant ionic lattice. Covalent: sharing of electrons, non-metal + non-metal, forms simple molecules or giant covalent structures. Metallic: delocalised electrons, metal atoms, forms a giant metallic structure.