Ionic Bonding: The electrostatic attraction between oppositely charged ions.
- Ionic bonding occurs between metals and non-metals, the metal loses electrons to become positively charged, the non-metal gains electrons and becomes negatively charged.
- Ionic bonding produces giant ionic lattices, this is because each ion is surrounded by oppositely charged ions.
Properties of ionic compounds:
- Solids at room temperature.
- High melting and boiling points as large amounts of energy are required to break the strong ionic bonds.
- Ionic compounds can't conduct electricity in a solid state as no ions can move, however when molten or in solution, they can conduct electricity as the ions can move.
Covalent Bond: Bonds formed by a shared pair of electrons.
- Covalent bonds are formed between two non-metals.
- A dative covalent bond can be formed when one atom provides both bonding electrons.
Properties of Covalent Structures:
- Simple molecular structures are made up of small, simple molecules. The molecules are held together by weak intermolecular forces, and the atoms within each molecule are held together by covalent bonds.
- These have low melting/boiling points because the intermolecular forces are weak and easy to break.
- They don't conduct electricity as there are no charged particles free to move.
- Solvent in non-polar solvents as van der Waals' forces form between the simple molcular structure and the solvent.
Giant Covalent Structures
Diamond, graphite and SiO2 are examples of a giant covalent lattice.
- High melting and boiling points as high temperatures (large amounts of energy are required to break the strong covalent bonds in the lattice.
- All giant covalent structures except graphite are non-conductors of electricity as the charged particles are not free to move.
- Giant covalent structures are insoluble in both polar and non-polar substances.
Permanent Dipole-Permanent Dipole Forces- The permanent dipole of one molecule attracts the permanent dipole of another to form a weak permanent dipole-permanent dipole force.
van der Waals' Forces- Formed by the movement of electrons in their shells creating an uneven distribution of charge, and thus creating an instantaneous dipole across the molecule. This instantaneous dipole induces dipoles in surrounding molecules etc. The dipoles attract each other forming weak intermolecular forces.
- The more electrons, the larger the induced dipoles, the larger the attraction between molecules and the larger van der Waals' forces produced.
Hydrogen bonds- These form when an electron deficient H atom attracts a lone pair of electrons on an O or an N molecule. Hydrogen bonds only form between O-H and N-H.
- Ice is less dense than water as ice has an open lattice structure, holding the water molecules apart.
- Water has higher mp/bps than expected as hydrogen bonds must also be overcome.