Covalent bonding and electron domain and molecular geometries

Covalent Bonding

A covalent bond is formed when a pair of electrons is shared between two atoms. This is typically observed between non-metal elements.
Each bonded atom tends to create enough covalent bonds to fill up their outer electron shell. This is often referred to as following the octet rule.
Single, double, and triple covalent bonds can form, where one, two, or three pairs of electrons are shared respectively.
There are two types of covalent bonds: polar and non-polar. A non-polar covalent bond forms when the electronegativities of the two atoms are equal, while a polar covalent bond forms when the electronegativities are different, resulting in an unequal sharing of the electron pair.
Examples of covalent molecules include water (H2O), oxygen (O2), and carbon dioxide (CO2).

Electron Domain Geometries

The electron domain geometry of a molecule is determined by the number of electron domains around the central atom, where an electron domain can be a lone pair of electrons or a bond (single, double, or triple).
Simple geometries include linear (two electron domains), trigonal planar (three electron domains), tetrahedral (four electron domains), trigonal bipyramidal (five electron domains), and octahedral (six electron domains).
Lone pair electrons occupy more space than bonding pairs, causing the shape of the molecule to be different from the electron domain geometry.

Molecular Geometries

Molecular geometry is determined by the positions of only the atoms in the molecules, not the electron pairs.
The molecular geometry can differ from the electron domain geometry due to the presence of lone pair electrons. For example, a molecule with tetrahedral electron geometry might have a “bent” molecular geometry if there are lone pairs present.
Recognising the possible geometries based on the number of electron domains and the number of lone pairs is crucial. Common molecular geometries include linear, bent, trigonal planar, trigonal pyramidal, and tetrahedral.

It is important to familiarise with the key concepts presented here, understanding the formation and types of covalent bonds, recognising electron domain and molecular geometries, and predicting the geometry of a molecule based on its Lewis structure. Practice drawing the Lewis structures and determining the electron domain and molecular geometries of different molecules.