Structure 2.2.5-10 & 2.4

Difference in electronegativities of bonded atoms

Measure of the atom’s relative ability to attract a shared pair of electrons towards itself in a covalent bond

Between two different non-metal atoms with different electronegativites

Making the more electronegative atom appear as if it had a negative pole and the less electronegative atom appear as if it had a positive pole

Greater electronegativity difference

A permanent negative dipole, due to greater electronegativity

A permanent positive dipole, due to less electronegativity

The distribution of electrons throughout the whole molecule

Polar bonds within the molecule Molecular geometry

No polar bonds If polar bonds are arranged symmetrically and cancel each other out

If polar bonds are arranged asymmetrically, so don’t cancel each other out

Covalent network structures

Atoms held together by covalent bonds in a continuous 3D lattice

Different structural forms of the same element in the same physical state

Different bonding and structural patterns

Each carbon atoms are covalently bonded to four other carbon atoms in a tetrahedral shape, with each bond being of equal strength, and each atom packed in the most efficient way. Each carbon atom forms only single bonds

Most efficient way

Very hard, due to strong covalent bonds High melting point, due to strong covalent bonds Poor electrical conductor, as no free moving electrons Very good thermal conductor

Each carbon atom forms 3 single covalent bonds with other carbon atom, forming covalently bonded layers of atoms. The fourth electron is delocalised between layers, and can travel across them. London dispersion forces between layers are weak

High melting point, as carbon atoms are covalently bonded. Can conduct electricity due to free fourth electron Soft and slippery, as forces between layers are weak

Covalent network lattice

Covalent layer lattice

Trigonal planar

Tetrahedral