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In chemical terms, a single element is composed of only one type of atom, and cannot be broken down any further into its sub-atomic parts. Elements are characterised by the number of protons that are contained within the nucleus of the atom; thus if two atomic nuclei have the same number of protons they are the same element. All the types of elements we are aware of are ordered by their atomic number in the periodic table; this can help to demonstrate trends of elements with similar chemical properties also in their group (a vertical column) or period (a horizontal row). The atomic number explains the number of protons and therefore the positive charge in the nucleus. The periodic table also shows the relative atomic mass, which is most importantly used to calculate moles of that element.

An example of an extremely abundant element is hydrogen (H). Hydrogen is the first element in the periodic table, with one electron and one proton in its nucleus; however, it contains no neutrons. This means that its electronic configuration is 1s1.

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