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.


Meitnerium, symbol Mt, chemical element with atomic number 109. It is produced artificially by nuclear fusion (in which a chemical element with larger atoms is produced by fusing together smaller atoms from other elements). Each meitnerium atom has a very 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 109 meitnerium (Mt), which was previously called unnilennium, to honor Austrian Swedish physicist Lise Meitner, a pioneer in the field of nuclear fission (the splitting of atomic nuclei).

Meitnerium has the atomic number 109, which means that each Mt atom contains 109 protons in the nucleus. Scientists have created several isotopes of meitnerium, or forms of the element that contain different numbers of neutrons in the nucleus. For example, meitnerium-266 contains 109 protons and 157 neutrons (109 protons + 157 neutrons = atomic mass 266), and meitnerium-268 contains 109 protons and 159 neutrons.

Meitnerium was first created in 1982 by researchers at the Heavy-Ion Research Laboratory in Darmstadt, Germany, by nuclear fusion of the smaller elements bismuth (Bi) and iron (Fe). Because the meitnerium nucleus contains so many particles, meitnerium is unstable and undergoes spontaneous fission, a process in which the atom breaks into smaller “daughter” components. When the atom splits, it releases energy in the form of electromagnetic waves and electrically charged bits of matter. This energy is known as radiation (see Radioactivity).

German scientists at the Heavy-Ion Research Laboratory created meitnerium-266, an isotope with a lifespan of only 0.0068 seconds. The most stable isotope of element 109 is meitnerium-268, which has a lifespan of 0.14 seconds. By 1998 these two isotopes were the only confirmed isotopes of meitnerium.

Meitnerium belongs to Group 9 (VIIIb) on the periodic table, which also contains the naturally occurring elements cobalt (Co), rhodium (Rh), and iridium (Ir). Cobalt, rhodium, and iridium are shiny, silvery metallic elements with melting points above 1500° C (2732° F). Because elements in the same group, or column, on the periodic table often share similar properties, scientists expect meitnerium to share properties with other Group 9 elements. However, because of the limited amount of meitnerium that can be produced and its short lifespan, scientists have been unable to determine chemical properties of this unstable element.