| element (chemical) |
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One of the basic materials of the universe, each of which is characterized by having a different number of protons in the atomic nucleus (the atomic number). Isotopes of the same element differ in the number of neutrons in the nucleus. There are 90 elements occurring naturally on Earth. Some, uranium for example, have no stable isotopes. Other radioactive elements can be created artificially. See also: atom, nucleosynthesis. |