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.


Xenon, symbol Xe, colorless, odorless gaseous element with an atomic number of 54. In group 18 (or VIIIa) of the periodic table, xenon is one of the noble gases.

Xenon was discovered in 1898 by the British chemists Sir William Ramsay and Morris Travers. It was formerly believed to be chemically inert, but since 1962 several compounds of xenon have been prepared. Xenon is used principally in such lighting devices as high-speed photographic tubes. Xenon is present in the atmosphere in minute amounts.

Xenon melts at -111.8° C (-169.2° F), and boils at -108.1° C (-162.6° F). The atomic weight of xenon is 131.29.