Category Science

               Matter exists in three states: solid, liquid and gas. The molecules in all matter are in constant motion, and in a gas they are held together so loosely that they can move freely. Gas molecules move about rapidly and at random. This means that a gas will expand to fill any space it occupies. The molecules in a gas press against anything that restrains them, causing pressure. As a gas is heated, the molecules move further apart and move about more rapidly. If it is restricted in a container, the pressure will increase. If any gas is cooled sufficiently, it will condense into a liquid. This is why some of the outer planets of the solar system are composed of liquid methane and hydrogen.

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               Radioactivity can contain large amounts of energy, which causes damage to matter, including living cells. These forms of radioactivity can knock electrons out of the atoms of a substance to produce ions, which have different properties.

               Organic compounds always contain the element carbon. Carbon compounds often have a very complicated structure, and they are responsible for most of the chemical reactions that sustain life. Carbon is found in some very large molecules, such as those in proteins and plastics. It has proved relatively easy to manufacture many of these substances artificially.

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               New elements are created by bombarding other elements with radiation in an atomic reactor. Scientists have made 16 artificial elements by bombarding uranium and other radioactive elements.

               Radioactivity is a form of energy given off by some types of atom with a high atomic number, such as uranium, radium and plutonium. Some forms of radiation consist of protons and neutrons bound together, while other forms consist of electrons or other particles called positrons. As radiation is emitted, the loss of particles from the original atoms changes their properties to those of another atom with a lower atomic number.

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Hydrogen is the lightest and simplest element, and its atomic number is 1. Uranium is the heaviest and its atomic number is 92 — indicating that it has 92 protons in each atom.

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