Why are metals conductive?

High density, metallic bonds

Explanation:

We may look at this question from the structural properties of the metals:

metals in their solid states are the most dense phases of all the standard phases we know (solids, liquids and gases). This means the particles within a metal lattice are very closely packed. Both heat and electricity is conducted when particles interact and touch one another, so that either energy or electric current might travel from one particle to the other easily. High density means low distances between the atoms, so they can interact easily; the main reason, however, is the fact that metals form metallic bonds, also known as 'sea of electrons'. We have metal cations floating in a sea of their valence electrons. This forms a medium in which both heat and electricity can travel easily.