alkali metals have low electronagetivity hence they can lose electrons easily. lithium can even force hydrogen to accept electrons. to my knowledge only alkali metals form stable binary hydrides . this is because thier outer most electron is not coupled,and is effectively shielded. you shouldn't touch Na because it keeps reacting with moisture in air and can react with the same on u'r skin(i have touched it its quite hot in air).nacl is hard because of strong electrostatic attraction while Na have mettalic one.