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.


Lawrencium, symbol Lr, artificially created radioactive metallic element with an atomic number of 103. Lawrencium is one of the transuranium elements of the periodic table. Named in honor of the American physicist Ernest Lawrence, it was discovered in 1961 at the Lawrence Berkeley National Laboratory of the University of California by American chemist Albert Ghiorso and his colleagues. A mixture of californium isotopes was bombarded with boron ions to produce short-lived lawrencium isotopes. Isotopes with mass numbers from 255 to 260 have been prepared. The most stable isotope, with a half-life of about 3 minutes, has a mass number of 260. Only small amounts of lawrencium have been produced. See also Radioactivity.