Europium 
Europium is a ductile metal with a hardness similar to that of lead . It crystallizes in a body-centered cubic lattice. [7] Some properties of europium are strongly influenced by its half-filled electron shell . Europium has the second lowest melting point and the lowest density of all lanthanides. [7]Allotropes
Some elements exist in several different structural forms, called allotropes. Each allotrope has different physical properties.

Europium