The ammonium ion NH4+ is formed when ammonia NH3 gains a proton H+ . In the ammonium ion, the central nitrogen atom is bonded to four hydrogen atoms, and it has a positive charge.Geometry:The electron-pair geometry of NH4+ is tetrahedral, as it has four bonding pairs of electrons around the central nitrogen atom. The molecular geometry is also tetrahedral, as all four electron pairs are involved in bonding with hydrogen atoms.Polarity:In the ammonium ion, the nitrogen-hydrogen bonds are polar due to the difference in electronegativity between nitrogen 3.04 and hydrogen 2.20 . However, the overall molecule is nonpolar because the four N-H bonds are arranged symmetrically in a tetrahedral shape, causing the individual bond dipoles to cancel each other out. As a result, the ammonium ion NH4+ is nonpolar.