In a 32-column table arranged by ascending atomic number, lanthanum (atomic number 57) follows barium (number 56) to start the f-block, with actinium below it.

Barium is a metal in group IIA of the periodic table with atomic number 56, an atomic weight of 137.34, and a density of 3.5 Mg/m 3. Its melting point is 714 C, and it boils at 1640 C. The electronic ...

Even the rarest rare earth, thulium, with atomic number 69, is 125 times more common than gold. And the least-rare rare earth, cerium, with atomic number 58, is 15,000 times more abundant than gold.