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Phases of Matter X - Elements, Compounds, and Mixtures

Normal matter (not exotic matter like black holes or neutronium) is either an element, compound of two or more elements, or a mixture of elements, compounds, or both. This sounds pretty basic, but is important and will be needed for future installments.The classic definition of an element goes something like, “a material that cannot be decomposed into simpler materials”. That is pretty good, but a more fundamental one is that an element is a material composed of atoms that all have the same atomic number. (The atomic number is the number of protons in the nucleus). This is a better definition because we now know that we can fission uranium, for example, into simpler elements.

Elements come in several varieties, called isotopes. While atoms in an element all contain the same number of protons, they can differ in the number of neutrons (uncharged particles, protons have a single positive charge). Only one stable element has no neutron in its nucleus, and that is the common isotope of hydrogen, the nucleus of which consists of a single proton. Another isotope of hydrogen, called deuterium, contains a proton and a neutron, while a third isotope, tritium, contains a proton and two neutrons. Tritium is radioactive and must be produced artificially. One way that can be done is to bombard lithium with neutrons. This is how thermonuclear bombs work.

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