 Metallic bonding occurs between metal atoms. The valence electrons of a metal atom have a low ionization energy and the atom itself has low electronegativity. This means that the valence electrons are not strongly tied to their parent atom and this leads us to a model of metallic bonding called the electron C model. When metal atoms are close to one another they no longer behave like neutral atoms. Instead the valence electrons can leave their parent atom and move around forming a C of delocalized electrons between the atoms. Because each atom has lost valence electrons it's now a positive ion. As a consequence there's an electrostatic attraction between the metal cations and the C of negatively charged electrons. And because the electron C is able to move freely all around the metal cations we say that this form of bonding is non-directional because the electrostatic attraction operates in all directions.