2.(1) Fundamental constituent part or principle. (2) One of the unique and basic types of matter which alone or in combination make up all natural and synthetic substances. At present 110 elements are known and theoretically many more are possible, 81 of these are stable (non-radioactive) and 92 occur naturally (the other 18 are synthesized in particle accelerators). They are divided into three main groups: metals (75 percent of the total), non-metals, and metalloids (weakly metallic). The fundamental part of an element is called an atom, whereas that of a compound is called a molecule.
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