Types of Chemical Bonds

Covalent bonding

Covalent bonding occurs when atoms share one or more pairs of electrons. This generally happens between non-metals.
A simple example is a molecule of oxygen (O2), where each oxygen atom shares two electrons with the other, forming a double bond.
If only one pair of electrons is shared, it’s a single bond (as in H2). If three pairs are shared, it’s a triple bond (as in N2).
In a covalently-bonded molecule, the shared electrons are attracted towards both nuclei, which helps to hold the atoms together.
Water (H2O), methane (CH4), and carbon dioxide (CO2) are examples of molecules with covalent bonds.

Ionic bonding involves the transfer of electrons from one atom to another. This generally happens between metals and non-metals.
A metal atom can lose an electron (or more) to a non-metal atom, creating a positively-charged cation and a negatively-charged anion.
These oppositely-charged ions attract each other due to electrostatic forces, forming ionic bonds.
Sodium chloride (NaCl) is a classic example of an ionic compound. Sodium loses an electron and becomes a Na+ cation, whereas chlorine gains an electron to become a Cl- anion.

Metallic bonding occurs in metals, where electrons are shared amongst a lattice of positive ions.
These free electrons form a ‘sea of electrons’ that can move freely around the metal lattice, leading to properties such as good electrical conductivity and malleability.
Classic examples of metallic bonding are pure metals like iron (Fe), copper (Cu), and aluminium (Al).

Hydrogen bonding is a type of dipole-dipole interaction that occurs when a hydrogen atom bonded to a highly electronegative atom (e.g. oxygen, nitrogen or fluorine) is attracted to another electronegative atom in a different molecule.
Although weaker than ionic or covalent bonds, hydrogen bonds are significantly stronger than other types of intermolecular forces.
Hydrogen bonding is responsible for many of water’s unique properties, including its relatively high boiling point and its ability to dissolve many substances.

London dispersion forces are weak intermolecular forces that exist between all atoms and molecules.
They arise due to temporary fluctuations in the electron distribution, which create instantaneous dipoles that induce dipoles in neighbouring atoms or molecules.
The strength of London dispersion forces increases with the size and complexity of the atoms or molecules involved, but they are generally much weaker than other types of bonding.