An element is a pure chemical substance comprising of one type of atoms. Elements are distinguished by their atomic number, derived from the number of protons present in the nucleus of an atom of a particular element. There are 118 known elements, 98 of them occur naturally on the earth while the remaining have been produced artificially during nuclear reactions. The 98 naturally occurring elements are further divided between metals, non-metals and metalloids, on the basis of their chemical and physical properties. When two different elements combine chemically, they form a chemical compound. Helium and hydrogen, present at the top of the periodic table, are the lightest chemical elements.
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The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. Atoms of similar or different elements come together to make molecules and compounds. For example two hydrogen molecules combine together to form a hydrogen molecule, while hydrogen and oxygen atoms combine chemically to make a new compound - water, that exhibits properties totally different from those of hydrogen and oxygen.
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