Chemistry - 3.1.3: Bonding

Ionic bond

Electrostatic force of attraction between anions and cations

Covalent bond

Strong electrostatic force of attraction between the nuclei of 2 atoms and a shared pair/pairs of electrons

Metallic bond

Electrostatic force of attraction between cations (positive metal ions) and sea of delocalised electrons

Dative covalent bond

A covalent bond where one atom supplies both electrons required to form a covalent bond

Requirements for formation of a dative covalent bond (2)

• One atom must have a vacant orbital

• Another atom must have a lone pair of electrons

Dimer/dimerisation

When two of the same small molecule join together via dative covalent bonding

3 types of intermolecular forces from weakest to strongest

• Van der Waals forces of attraction

• Dipole-dipole interactions

• Hydrogen bonds

Van der Waals forces of attraction

The weakest intermolecular force. Caused by the movement of electrons within a molecule

Factors determining strength of VdWs (2)

• Size of the molecule - bigger molecule = more electrons = stronger VdWs foa between molecules

• Shape of the molecule - straighter chains can pack together closer = stronger VdWs foa between molecules

Electronegativity

The ability of an atom to draw electron density towards itself in a covalent bond

Dipole-dipole interactions depend on:

• Presence of electronegative atoms resulting in polar bonds

• Shape of molecule - distribution of charge must be asymmetric - overall dipole moment

Hydrogen bonding

The strongest intermolecular force. Happens between molecules containing H directly bonded to F, N or O.

Factors affecting electronegativity (2)

• Nuclear charge

• Atomic radius

Deviations from perfect ionic model (i.e. covalent character of ionic bonds) require:

• A polarising cation - small, highly charged ion

• A polarisable anion - larger, diffuse ion

Shape of molecules containing 2 bonding pairs

Linear

Shape of molecules containing 3 bonding pairs

Trigonal planar

Shape of molecules containing 4 bonding pairs

Tetrahedral

Shape of molecules containing 5 bonding pairs

Trigonal bipyramidal

Shape of molecules containing 6 bonding pairs

Octahedral