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In 1895, French chemist Henri Moissan attempted to form a reaction between fluorine, the most electronegative element, and argon, one of the noble gases, but failed.Scientists were unable to prepare compounds of argon until the end of the 20th century, but these attempts helped to develop new theories of atomic structure.In 1902, having accepted the evidence for the elements helium and argon, Dmitri Mendeleev included these noble gases as group 0 in his arrangement of the elements, which would later become the periodic table.Ramsay continued to search for these gases using the method of fractional distillation to separate liquid air into several components.Noble gases have the largest ionization potential among the elements of each period, which reflects the stability of their electron configuration and is related to their relative lack of chemical reactivity.

A century later, in 1895, Lord Rayleigh discovered that samples of nitrogen from the air were of a different density than nitrogen resulting from chemical reactions.

A helium-oxygen breathing gas is often used by deep-sea divers at depths of seawater over 55 m (180 ft) to keep the diver from experiencing oxygen toxemia, the lethal effect of high-pressure oxygen, nitrogen narcosis, the distracting narcotic effect of the nitrogen in air beyond this partial-pressure threshold, and carbon dioxide poisoning (hypercapnia), the panic-inducing effect of excessive carbon dioxide in the bloodstream.

After the risks caused by the flammability of hydrogen became apparent, it was replaced with helium in blimps and balloons.

For example, argon is used in light bulbs to prevent the hot tungsten filament from oxidizing; also, helium is used in breathing gas by deep-sea divers to prevent oxygen, nitrogen and carbon dioxide (hypercapnia) toxicity.

The properties of the noble gases can be well explained by modern theories of atomic structure: their outer shell of valence electrons is considered to be "full", giving them little tendency to participate in chemical reactions, and it has been possible to prepare only a few hundred noble gas compounds.