Since a covalent bond is formed by sharing electron pairs, the attraction is between positive nuclei and the shared electron pairs. The number of bonds depends on the number of valence electrons of the atom.
When a material is heated, the kinetic energy of that material increases and its atoms and molecules move about more. This means that each atom will take up more space due to its movement so the material will expand. ... Some metals expand more than others due to differences in the forces between the atoms / molecules.
