Covalent structures

Covalent Bonding

Covalent bonding involves the sharing of electron pairs between atoms. These shared electrons are counted as part of each atom’s valence electrons, helping them attain stable noble gas configurations.
Covalent bonds form predominantly between non-metal atoms.
The atoms linked by covalent bond are called a molecule. For example, water molecule (H2O) has covalent bonds between two hydrogen atoms and one oxygen atom.
It’s important to distinguish between single, double, and triple covalent bonds. These refer to the number of shared electron pairs between two atoms, which in turn affect the bond’s strength and length.

Covalent Structures

There are two types of covalent structures: simple molecular and giant covalent structures.
Simple molecular structures consist of a fixed number of atoms connected by covalent bonds in a certain arrangement. These molecules are usually small, and include water (H2O), carbon dioxide (CO2), and methane (CH4).
In giant covalent structures, also known as macromolecular structures, a huge number of atoms are linked by covalent bonds in a continuous network extending in three dimensions. Examples include diamond and graphite, which are forms of carbon, and the strongest naturally occurring mineral, silicon dioxide (SiO2 or quartz).

Properties of Covalent Compounds

Simple molecular structures have low melting and boiling points. This is because the attractive forces between their molecules (intermolecular forces) are generally weak and therefore easily overcome with little energy.
However, giant covalent structures have very high melting and boiling points due to their continuous network of covalent bonds, which requires a significant amount of energy to break.
Unlike ionic compounds, covalent compounds in the solid state do not conduct electricity. This is because they do not have free moving ions or electrons.
An exception to this rule is graphite, a form of carbon with a structure that allows for the movement of electrons, thus giving it the ability to conduct electricity.

In the study of covalent bonding, it’s key to understand the concept of electron sharing, predict bond types and molecular geometry, and explain the physical properties of substances with simple molecular and giant covalent structures. Take time to practice drawing dot-and-cross diagrams, and familiarise yourself with common molecules and their structures.