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element
(elīә-mәnt)
any of the primary parts or constituents of something.
in chemistry, a simple substance that cannot be decomposed by ordinary chemical means; elements are the basic components of
which all matter is composed. Chemical elements are made up of atoms, each of which consists of a nucleus with a cloud of negatively charged electrons revolving around it. The two major components of the nucleus are protons and neutrons. The number of protons in the atoms of a particular element is always the same, and therefore the physical and chemical properties
of the element are always the same. It is possible, however, for a chemical element to exist in several different forms (called
isotopes), the difference depending on the number of neutrons in the nucleus of its atoms. There are at least 105 different chemical
elements known. The atomic number of an element is determined by the number of protons in the nucleus of one of its atoms. The mass number of an isotope is
determined by the total number of neutrons and protons in the nucleus.
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