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.


Lutetium, symbol Lu, silvery white metallic element with an atomic number of 71. Lutetium is one of the transition elements of the periodic table.

Lutetium was discovered independently by two investigators, the French chemist Georges Urbain in 1907 and the Austrian chemist Carl Auer von Welsbach about the same time. It was named by Urbain, who derived the word from Lutetia, the ancient name of Paris. Lutetium occurs in various rare earth minerals, usually associated with yttrium. It is the rarest of the rare earth elements and ranks 59th in order of abundance of the elements in the earth's crust. Several trivalent salts are known. A natural radioactive isotope of lutetium that has a half-life of about 30 billion years is used in determining the age of meteorites in relation to the age of the earth.

Lutetium melts at about 1663° C (about 3025° F), boils at about 3402° C (about 6156° F) and has a specific gravity of 9.84. The atomic weight of lutetium is 174.97.