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.


Seaborgium, symbol Sg, chemical element with the atomic number 106. Seaborgium is produced artificially by nuclear fusion (in which an element with larger atoms is produced by fusing two smaller atoms from other elements). Each seaborgium atom contains a large nucleus, or central mass, containing positively charged particles called protons and neutral particles called neutrons. The large number of particles in the nucleus makes the atom unstable and causes the atom to split apart into smaller components soon after it is created. The International Union of Pure and Applied Chemistry named element 106 seaborgium (Sg) to honor Nobel Laureate Glenn T. Seaborg, who codiscovered plutonium and nine other transuranium elements. Seaborgium, which was previously called unnilhexium, is the first element that was named for a living person.

Seaborgium has the atomic number 106, which means that each Sg atom contains 106 protons in the nucleus. Scientists have created several isotopes of seaborgium, or forms of the element that contain different numbers of neutrons in the nucleus. For example, seaborgium-263 contains 106 protons and 157 neutrons (106 protons + 157 neutrons = atomic mass 263). Similarly, seaborgium-265 contains 106 protons and 159 neutrons.

Seaborgium belongs to Group 6 (VIb) on the periodic table, which also contains the naturally occurring (nonradioactive) elements chromium (Cr), molybdenum (Mo), and tungsten (W). Both chromium and molybdenum are important trace elements (elements that are vital for health but occur in the body in very small amounts) and are key components of certain proteins and enzymes. Because elements in the same group, or column, on the periodic table often share similar properties, scientists expected seaborgium to share properties with other Group 6 elements.