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.


Indium, symbol In, soft, malleable, silvery white metallic element. The atomic number of indium is 49; the element is in group 13 (or IIIa) of the periodic table.

Indium was discovered spectroscopically in 1863 by the German chemists Hieronymus Theodor Richter and Ferdinand Reich. It ranks 63rd in order of abundance of the elements in the surface of the earth. Indium melts at about 157°C (about 315°F), boils at about 2080°C (about 3776°F), and has a specific gravity of 7.3. The atomic weight of indium is 114.82.

Indium never occurs as a free metal and is usually found as the sulfide; in certain zinc blendes; and in tungsten, tin, and iron ores. It is used as an alloying agent with nonferrous metals, in bearing alloys, and in nuclear-reactor control rods. Certain indium compounds have unique semiconductor properties.