• When non-metals react with one another, they share electrons instead of transferring them just as in the diatomic elements.

• The bond formed by sharing of electrons between non-metals is the covalent bond.

• Sharing of one pair of electrons, i.e. two electrons, forms one covalent bond. Hydrogen has one covalent bond while nitrogen has three.

• One covalent bond is represented by one line in the structural formula.

• Compounds linked by covalent bonds are called covalent compounds or molecular compounds. Water, carbon dioxide, and methane are examples.

• Within each molecule of a simple molecular compound, there are weak intermolecular forces of attraction so they have low densities, and melting and boiling points.

• Most simple molecular compounds are soluble in organic solvents but not in water.

• They do not conduct electricity in any state due to lack of mobile electrons/ions.

GIANT MOLECULAR STRUCTURES

• Diamond and graphite, allotropes of carbon have giant covalent structures.

• Giant molecular structures are usually solids at r.t.p, have high melting and boiling points, and high densities, and do not conduct electricity in any state (except graphite).

• Graphite is slippery so it is used as a lubricant while diamond is hard and shiny so it is used for cutting purposes.

• Sand (silicon dioxide) is another giant molecular structure.

Common prefixes to name covalent compounds are mono, di, tri, tetra, penta and hexa.

METALLIC BONDING

• In metals, electrons break free of the atoms forming cations and become delocalised themselves. The electrons and cations attract each other due to opposite charges on them.

• The force of attraction between positive metal ions and ‘sea’ of delocalised electrons is the metallic bond.

• Since there are a lot of free electrons that move throughout the metallic structure, metals are good conductors of heat and electricity.

• Metals are ductile and malleable because when force is applied, layers of atoms can slide over one another without disrupting the structure.

• Due to strong forces of attraction between electrons and ions, metals have high melting and boiling points, and densities (exception: Group I)