Ionization Energy

The first ionization energy is the energy required to completely remove an electron from a neutral atom. Ionization energy generally decreases as we move down a group. Because the outermost electrons are increasingly distant from the nucleus, less energy is required to completely remove the first one. As we move from left to right in a given row, the ionization energy increases dramatically because of increasing effective nuclear charge. Notice the periodic character of the change in ionization energy as we move across each row. As we move across the first transition element series, the ionization energies increase slowly in proceeding toward the right. The same trend in increasing ionization energy across the transition series is observed in the second long row consistent with the periodic character of this property. However, ammonia is a weak base. The equilibrium forming the hydroxide and ammonium ions lies largely to the left. At any given time, most of the ammonia in solution exists as NH3 molecules rather than as ammonium and hydroxide ions.