Cerium is especially interesting because of its variable electronic structure. The energy of the inner 4f level is nearly the same as that of the outer (valence) electrons, and only small amounts of energy are required to change the relative occupancy of these electronic levels. This gives rise to dual valency states..
Melting point: 798 °C Boiling point: 3443 °C
A foil is a thin sheet of pure metal. Given its fragile nature, some foils have protective coatings.