Animation showing the structure of a metallic lattice. At the start we see one atom of magnesium, comprising a positively charged nucleus (red) and two orbiting outer electrons (blue). The view then pulls back to show the regular arrangement of atomic nuclei in the metallic lattice structure. The electrons are seen to be delocalised, that is, they do not orbit a particular nucleus, but instead can move freely about the entire lattice structure, as a \sea\ of electrons. This mobility is responsible for the electrical conductivity of metals. When an external electric field is applied, the negatively charged electrons are attracted to the positive side of the applied field, at the right of the frame here.