Answer:
Closely packed cations with loosely held valence electrons
Step-by-step explanation:
Pure metals contain so-called metallic bonds. These metallic bonds are often referred to as sea of electrons. Metals consist of closely packed cations (and, hence, that's why they have a high density) with loosely held valence electrons (this is the reason why metals tend to lose their electrons rather than gain, besides, it's also the reason why the first ionization energy for the metals is relatively low).