There are over 100 chemical elements; however some are only found inside nuclear reactors, these have very short half-lives.
Each element has its own “Atomic Number” which is equal to the number of protons in the nucleus of the atom. The simplest element is Hydrogen which has an Atomic Number of 1 since it only has one proton.
In an atom there is always the same number of electrons as protons; but atoms can be ionised. If electrons are removed from an atom a positive ion (cation) is formed. If electrons are added to an atom a negative ion (anion) is formed.
Chemical elements can be arranged in a table according to the number of protons and the pattern of electrons orbiting the atoms nucleus.
Columns of elements in the periodic table are called Groups. Elements in the same group have similar chemical properties.
Group I contains the Alkali Metals: Li Na K Rb Cs Fr
Group II contains the Alkaline Earth Metals: Be Mg Ca Sr Ba Ra
Group III contains: B Al Ga In Tl
Group IV contains: C Si Ge Sn Pb
Group V contains: N P As Sb Bi
Group VI contains: O S Se Te Po
Group VII contains the Halogens F Cl Br I At
Group VIII contains the Inert Gases or Noble Gases: He Ne Ar Kr Xe Rn