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.


Bromine, symbol Br, poisonous element that at room temperature is a dark, reddish-brown liquid. In group 17 (or VIIa) of the periodic table, bromine is one of the halogens. The atomic number of bromine is 35.

Bromine is widely distributed in nature. It melts at -7.25° C (18.95° F), boils at 58.78° C (137.8° F), and has a specific gravity of 3.10; the atomic weight of the element is 79.90. Bromine is so similar in its chemical properties to chlorine, with which it is almost invariably associated, that it was not recognized as a separate element until 1826, when it was discovered and isolated by the French chemist Antoine Jérôme Balard.

Bromine is very soluble in a wide variety of organic solvents, such as alcohol, ether, chloroform, and carbon disulfide. It reacts chemically with many compounds and metallic elements and is slightly less active than chlorine.

Bromine does not occur in nature as a free element, but is found in bromide compounds. It was formerly a by-product of the production of common salt or of potassium from brines rich in bromides. Elemental bromine can be prepared from bromides by treatment with manganese dioxide or sodium chlorate. Increasing demand has led to the production of bromine from seawater, which contains on the average 65 parts of bromine per million.

Bromine has been used in the preparation of certain dyes and of dibromoethane (commonly, ethylene bromide), a constituent of antiknock fluid for leaded gasoline. Bromides are used in photographic compounds and in natural gas and oil production.