Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Terbium, symbol Tb, metallic element with an atomic number of 65. Terbium is one of the rare earth elements in the lanthanide series of the periodic table.

Terbium was discovered in 1843 by the Swedish chemist Carl Gustav Mosander. It ranks about 58th in natural abundance among the elements in crustal rock. It occurs in minute quantities as a white oxide known as terbia, in such minerals as gadolinite. Terbium has potential applications in alloys, refractory (high-temperature) materials, and electronic apparatus.

Terbium melts at about 1356° C (about 2473° F), boils at about 3230° C (about 5846° F), and has a specific gravity of 8.23. The atomic weight of terbium is 158.925.