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In chemistry, a diatomic element is one that, when not chemically bonded with any other elements, will form a molecule having two atoms of the element, such as H2 or O2. Diatomic molecules rarely exist in their atomic form. They include most of the molecular elements or polyatomic molecules. Earth's atmosphere is comprised almost completely (99%) of diatomic oxygen and diatomic nitrogen.
The eight diatomic elements are hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, iodine and astatine. These elements, with the exception of hydrogen, when located on the periodic tableThe periodic table of the chemical elements is a tabular display of the known chemical elements. The elements are arranged by electron structure so that many chemical properties vary regularly across the table. Each element is listed by its atomic number, form a numeral "7".
Mnemonics that can be used are "(Mr.) Brinklehoff", which is the pronunciation of "BrINClHOF" and "Have No Fear Of Ice Cold Beer", however these were 'composed' before the discovery that astatine was diatomic was made.
