Will magnesium and chlorine form a metallic bond?
A ionic bond will form. Magnesium will lose two electrons and the two chlorine atoms will pick up one atom each. It will become magnesium dichloride (MgCl2). I believe that a polar - covalent bond will form. .3 to1.7 difference in electronegativity is polar covalent. and when you subtract the electronegativity of the two elements you get .5 and that falls in the polar covalent area.
Magnesium atoms, which form divalent cations, can each bond ionically with two chloride ions, because chlorine atoms form anions with only one negative charge each. ("Chloride atoms" as written in the question do not exist: chlorine atoms form chloride ions by gaining one electron each from less electronegative atoms.)