Covalent Bonding

Covalent Bonding

Covalent bonding is a formation of two atoms sharing a pair of electrons. This type of bonding happens in most non-metal elements as well as in compounds formed among non-metals. These shared electrons are found in the outer shells of the atoms. Usually, each atom gives one electron to the shared pair of electrons.

Molecules

Many of the covalently bonded substances are made up of small molecules. A molecule is a group of two or more atoms joined together by covalent bonds. Molecules of the same element or compound always contain the same number of atoms of each element. The atoms in a molecule are always joined together by a covalent bond. Substances that are made up of ions do not form molecules.

Atoms form covalent bonds by sharing electrons to get a full outer shell. This means that the number of covalent bonds an atom can form is the same as the number of electrons needed to get a full outer shell.

Double and Triple Bonds

Some molecules contain a double bond, which consists of two shared pairs of electrons. For example, oxygen molecules consist of two oxygen atoms joined together. Oxygen atoms can form two covalent bonds, so to link the two oxygen atoms together, a double bond forms between them.

Properties

A substance with small molecules has strong covalent bonds that hold the atoms together in its molecules. There are weak forces between molecules and their neighbours. The structure and bonding of substances with small molecules explains their properties.

Low Melting and Boiling Points

Most substances with simple molecules have low melting points and boiling points. Many are in the liquid or gas state at room temperature.

Energy must be transferred to a substance to make it melt or boil. This energy overcomes the attractive forces between the particles in the substance:

some forces of attraction are overcome during melting, allowing molecules to move over each other

more of the forces of attraction are overcome during boiling, allowing the molecules to move freely away from each other

The more energy that is needed, the higher the melting point or boiling point.