Unshared electron pairs, also known as non-bonding pairs, are valence electrons that are not involved in chemical bonding with other atoms within a molecule. These electrons remain exclusively associated with a single atom. For example, in a water molecule (HO), the oxygen atom has two pairs of electrons not involved in bonding with the hydrogen atoms. These are unshared electron pairs.
The presence of unshared electron pairs significantly influences molecular geometry and reactivity. The electron pairs exert a repulsive force, impacting bond angles and overall molecular shape. Furthermore, these electrons contribute to the molecule’s polarity and can act as nucleophilic sites, making the molecule susceptible to chemical reactions with electrophiles. Historically, understanding their existence has been critical to developing accurate models of chemical bonding and predicting molecular behavior.
