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.


Lithium, symbol Li, silvery white, chemically reactive metallic element that is the lightest in weight of all metals. In group 1 (or Ia) of the periodic table (see Periodic Law), lithium is one of the alkali metals. The atomic number of lithium is 3.

Discovery of the element is generally credited to Johann A. Arfvedson in 1817. Chemically, lithium resembles sodium in its behavior. Lithium is obtained by the electrolysis of a mixture of fused lithium and potassium chloride. It tarnishes instantaneously and corrodes rapidly upon exposure to air; when it is stored it must be immersed in a liquid such as naphtha. Lithium ranks 35th in order of abundance of the elements in the crust of the earth. It does not occur in nature in the free state but only in compounds, which are widely distributed. The metal is used as a deoxidizer and to remove unwanted gases during the manufacture of nonferrous castings. Lithium vapor is used to prevent carbon dioxide and oxygen from forming scale in furnaces in heat-treating steel. Important compounds of lithium include the hydroxide, used for bonding carbon dioxide in the ventilator systems of spacecraft and submarines; and the hydride, used to inflate lifeboats, and its heavy hydrogen (deuterium) equivalent, used in making the hydrogen bomb. Lithium carbonate, a common mineral, is used in the treatment of bipolar disorder and some forms of depression.

Lithium melts at about 181° C (about 358° F), boils at about 1342° C (about 2448° F), and has a specific gravity of 0.53. The atomic weight of lithium is 6.941.