There are about 100 elements known to scientists at present. About 90 occur naturally in the earth.
Every substance on earth is made from these elements. Each element has a symbol, consisting of one or two letters, to represent its name.
The elements above number 103 have a symbol consisting of three letters to represent their names. For example, number 105 is called unnilipentium, symbol Unp.
Some naturally occurring elements are radioactive, for example, radium.
Plutonium and the other elements above 92 are made in nuclear reactors.
Some elements are named after scientists, e.g. einsteinium, and others after places, e.g. californium.
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