What property of nonmetallic elements makes more likely to gain electrons than lose electrons?
Non-metals already have outside shells that are more than half filled (escept for group 4 elements) and it is easier to fill the shell by adding 2 or 3 electrons than to lose 5 or 6 electrons. For example, oxygen has an outer shell of 6 electrons. It is EASIER to gain two electrons than to lose all 6 of its electrons.