1. Nitrogen's electronegativity: Nitrogen is more electronegative than hydrogen. This means it attracts electrons more strongly in a covalent bond. In the ammonium ion, nitrogen pulls the shared electrons closer to itself, creating a partial negative charge on nitrogen and partial positive charges on the hydrogens.
2. Nitrogen's lone pair: Nitrogen has five valence electrons and forms three covalent bonds with hydrogen atoms in ammonia (NH₃). This leaves one lone pair of electrons on nitrogen.
3. Protonation: When ammonia reacts with a proton (H⁺), the proton is attracted to the lone pair on nitrogen. This results in the formation of a fourth covalent bond between nitrogen and the proton.
4. Formal charge: Due to the addition of the proton and the sharing of the electron pair, the nitrogen atom in ammonium has four bonds and no lone pairs. This gives nitrogen a formal charge of +1.
5. Overall charge: The ammonium ion has a net positive charge because the +1 charge on nitrogen outweighs the four +1/4 charges on the hydrogens.
In summary, the positive charge on ammonium arises from the combination of nitrogen's electronegativity, the presence of a lone pair on nitrogen, and the addition of a proton to form a fourth covalent bond.
