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.


Ununhexium, artificially produced radioactive chemical element; symbol Uuh; at. no. 116; mass number of most stable isotope 292; m.p., b.p., sp. gr., and valence unknown. Situated in Group 16 of the periodic table, it is expected to have properties similar to those of polonium and tellurium.

In 1999 a research team at the Lawrence Berkeley National Laboratory in Calif. bombarded lead-208 atoms with high-energy krypton-86 ions to create, apparently, ununoctium (element 118) atoms. The Uuo-293 isotope that they synthesized emitted an alpha particle to decay into Uuh-289, which has a life-life of about 0.6 millisecond, which then emitted an alpha particle to decay into ununquadium (element 114). Although the Berkeley laboratory retracted its claim for creating ununoctium in 2001, other research teams have since created ununhexium directly. No name has yet been adopted for element 116, which is therefore called ununhexium, from the Latin roots un for one and hex for six, under a convention for neutral temporary names proposed by the International Union of Pure and Applied Chemistry (IUPAC) in 1980.