Covalent Bonds

Chemistry: IB Diploma Higher Level, topic 2.2.1

Covalent Bonding

Covalent bonding happens between non-metals.

A covalent bond is one that contains a shared pair of valence electrons.
Usually, each atom gives one electron to the bond.
Covalent bonds are formed between two atoms when both have similar tendencies to attract electrons to themselves
For example, when both atoms have identical or fairly similar ionization energies and electron affinities.

Molecules have covalent bonds holding the atoms together.
Covalent bonds are strong because the shared electrons are attracted to the nucleus of both atoms.
Because the attraction between molecules, which are electrically neutral, is weaker than that between electrically charged ions, covalent compounds generally have much lower melting and boiling points than ionic compounds.
In fact, many covalent compounds are liquids or gases at room temperature, and, in their solid states, they are typically much softer than ionic solids.
ost covalent compounds are insoluble in water; since they are electrically neutral, they are poor conductors of electricity in any state.

Atoms can also form double (e.g. O₂) or triple (e.g. N₂) covalent bonds.
There are rare examples of quadruple, quintuple, and even sextuple bonds between some heavy metal compounds.
Multiple bonds contain shared pairs of electrons just like single bonds.
Multiple bonds are usually stronger than single bonds.

A coordinate bond is a special kind of covalent bond.

A coordinate bond is a covalent bond in which both electrons in the bond come from one atom.
Coordinate bonds are sometimes called dative bonds.

Ammonium ions are made of an ammonia molecule that has attached to a hydrogen ion with its lone pair.
Both electrons for the coordinate bond come from the nitrogen atom.