The periodic table
Science World, May 7, 2007
The periodic table is a systematic way to organize Earth's elements, substances that consist of atoms of only one kind. Today, there are 112 known and named chemical elements. Elements are arranged according to their increasing atomic numbers. Hydrogen (H), for example, has an atomic number of 1 and is the lightest known natural element on Earth. Scientists have created elements with atomic numbers greater than 92, but they don't exist naturally. Some scientists think they may have created elements heavier than 112, but until an element is confirmed by two different labs, it usually isn't listed on the periodic table.
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