The best reason for why a covalent bond forms is A) two atoms exist as ions and the ions are attracted to each other. B) the atoms that form cations have low ionization energy and anions have high electron affinity, so the two atoms exchange electrons. C) nonmetal atoms cannot react with each other unless they share electrons. D) atoms with high electronegativities will not lose electrons, so instead they share electrons to reach a stable number of valence electrons.