Question

Why hydrogen ions are electro positive and OH ions are electro negative ??

Answer 1

Electronegativity is affected by two factors primarily: the charge density in the nucleus and the shielding effect of filled electron shells. The reason that fluorine is the most electronegative element on the periodic table is because it has a nucleus with 9 protons and 10 neutrons and it only has one filled shell beneath its valence electrons. This means that there is not much shielding from the filled shells preventing the positive charge of the nucleus from taking an electron from another element. In the case of hydrogen, they only need to gain or lose a single electron in order to have a filled valence shell. The reason that they don’t gain electrons very readily is that the H+ ion is very stable as opposed to the H- ion, which reacts easily to lose the electron it had gained.