Copper (Cu). Diagram of the valence orbitals of an atom of copper-64 (atomic number: 29), an isotope of this element. Copper is a transition metal in group 11, period 4, and the d-block of the periodic table. It has a melting point of 1084 degrees Celsius. The trends across the transition metals are due to electrons filling an inner d-subshell, shielding the outer (valence) electrons from the increasing nuclear charge.