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.


Element 116, also called ununhexium (Uuh), chemical element with atomic number 116. Each ununhexium atom has a nucleus, or inner core, containing particles called neutrons and protons (see Atom). The number of protons in the nucleus of an atom determines the element’s atomic number. The nucleus of an atom of ununhexium, therefore, contains 116 protons. Ununhexium has never been found in nature but can be produced in the laboratory by nuclear fusion (a process in which a chemical element with larger atoms is produced by fusing together two smaller atoms of other elements).

Scientists at the Joint Institute for Nuclear Research in Dubna, Russia, created the first atom of ununhexium in mid-2001. They produced ununhexium by using a machine called a particle accelerator to accelerate calcium atoms to a very high velocity and then smashing them into atoms of the element curium. In a very small percentage of these collisions, an atom of calcium combines with an atom of curium to form an isotope of ununhexium called ununhexium-292. Isotopes are varieties of an element that all contain the same number of protons in their cores but contain different numbers of neutrons. Ununhexium-292 contains 116 protons and 176 neutrons (116 + 176 = 292). The Dubna scientists have since produced additional atoms of the element, but their discovery has not yet been confirmed by another laboratory.

Atoms that contain many more than 200 protons and neutrons tend to be unstable and split apart into atoms of elements containing fewer protons and neutrons. This decay is called spontaneous fission, a process in which the atom breaks into smaller “daughter” components. In general, the more particles a nucleus contains, the quicker it tends to decay. Like most of the other known atoms with large numbers of particles packed into their nuclei, ununhexium-292 breaks down very quickly, taking an average of only about 76 milliseconds to decay.

Scientists have been unable to examine ununhexium’s chemical properties because of the limited amount of ununhexium-292 that has been produced and its short life span. Scientists suspect, however, that ununhexium’s properties will turn out to resemble those of the naturally occurring element polonium (Po). Ununhexium belongs to Group 16 (or VIa), a column of the periodic table that also contains polonium. Elements in the same group of the periodic table often share similar properties (a pattern known as the periodic law).

The International Union of Pure and Applied Chemistry has not yet approved permanent names to several recently discovered elements, including ununhexium. Ununhexium is a temporary name based on the element’s atomic number that uses Latin prefixes for the digits of the atomic number (un = 1, hex = 6) followed by the suffix -ium.