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.

Actinide Series

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Actinide Series, a series of 14 radioactive elements in the periodic table with atomic numbers 89 through 102. Only the first four elements in the series have been found in nature in appreciable amounts; the remainder have been produced synthetically. Those elements with atomic numbers of 93 and above are called transuranium elements. The elements constituting the actinide series are, in order of increasing atomic number, actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, and nobelium.