Ammonia (NH3) has a lone pair of electrons due to its molecular structure and the arrangement of its constituent atoms. In the ammonia molecule, nitrogen (N) is the central atom bonded to three hydrogen (H) atoms.
The molecular geometry of ammonia is trigonal pyramidal, meaning the three hydrogen atoms are arranged in a triangular fashion around the central nitrogen atom. The bond angles between the N-H bonds are approximately 107 degrees.
In the ammonia molecule, nitrogen has five valence electrons. It forms three sigma (σ) bonds with the three hydrogen atoms by sharing electrons, resulting in a complete octet for hydrogen (H) with two electrons each.
However, even after forming these three bonds, nitrogen still has one lone pair of electrons that is not involved in bonding. This occurs because nitrogen has one unshared pair of electrons that remain localized around the nitrogen atom, creating a region of electron density that is not involved in any chemical bonding.
The presence of this lone pair of electrons gives ammonia its characteristic properties, such as its ability to act as a Lewis base and form coordination complexes with other species. The lone pair can interact with other electron-deficient species, facilitating various chemical reactions and interactions.