Metals lose electrons easily, and non-metals gain electrons
easily. Metals are ductile; which means they can be stretched out
into wire, and non-metals are nonductile.
Metals differ from nonmetals merely in that they have a positive oxidation number. An element's oxidation number will be it's charge when it is ionized. For example when sodium (Na) is ionized it will lose 1 electron (to have a complete valance shell) losing this electron (a negative particle) will cause the atom to have a positive charge (and therefore a positive oxidation number too) Non metals will have negative oxidation numbers. When a non metal is ionized it will gain electrons (if it has more than four electrons in it's valence shell gaining electrons takes less energy) when it gains these negative particles it gains a negative charge. The oxidation number is determined by how many electrons are in the valence shell of an electrically neutral atom. Any less than four and the oxidation number is positive so you have a metal, more than four you have a non metal.