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.


Fermium, symbol Fm, artificially created radioactive element with an atomic number of 100. Fermium is one of the transuranium elements in the actinide series of the periodic table. The element was isolated in 1952 from the debris of a hydrogen bomb explosion by the American chemist Albert Ghiorso and coworkers. Subsequently fermium was prepared synthetically in a nuclear reactor by bombarding plutonium with neutrons and in a cyclotron by bombarding uranium-238 with nitrogen ions. Isotopes with mass numbers from 242 to 259 have been produced; fermium-257, the longest-lived of these isotopes, has a half-life of 80 days. The element was named fermium in 1955 in honor of the Italian American nuclear physicist Enrico Fermi. Fermium does not have any industrial applications. See also Radioactivity.