Editing Goldschmidt classification (section)

==Atmophile elements==
The atmophile elements ({{ety|grc|''{{lang|grc|[[wikt:ἀτμός#Ancient Greek|ἀτμός]]}}'' ({{Transliteration|grc|atmós}})|vapor, steam, smoke}}) are [[Hydrogen|H]], [[Carbon|C]], [[Nitrogen|N]] and the [[noble gas]]es.<ref>Pinti D.L. (2018) Atmophile Elements. In: White W.M. (eds) Encyclopedia of Geochemistry. Encyclopedia of Earth Sciences Series. Springer, Cham. doi:10.1007/978-3-319-39312-4_209</ref>

Atmophile elements (also called "[[Volatile (chemistry)|volatile elements]]") are defined as those that remain mostly on or above Earth's surface because they are, or occur in, liquids and/or gases at temperatures and pressures found on the surface. The noble gases do not form stable compounds and occur as [[monatomic gases]], while [[nitrogen]], although highly reactive as the free atom, bonds so strongly into diatomic molecular nitrogen that all [[oxide]]s of nitrogen are thermodynamically unstable with respect to nitrogen and oxygen. Consequently, with the [[Geological history of oxygen|development of free oxygen]] in Earth's atmosphere, [[ammonia]] was oxidised to molecular nitrogen which has come to form four-fifths of the Earth's atmosphere. Carbon is also classed as an atmophile because it forms very strong multiple bonds with [[oxygen]] in [[carbon monoxide]] (slowly oxidised in the atmosphere) and [[carbon dioxide]]. The latter is the fourth-largest constituent of the Earth's atmosphere, while carbon monoxide occurs naturally from various sources ([[volcano]]es, combustion) and has a [[Atmospheric residence time|residence time]] in the atmosphere of a few months.

Hydrogen, which occurs in water, is also classed as an atmophile. Water is classified as a volatile, because most of it is liquid or gas, even though it can exist as a solid compound at Earth's surface. Water can also be incorporated into other minerals as [[water of crystallization]] (as in [[gypsum]]) or through [[ionic bond|ionic]] and [[hydrogen bonding]] (as in [[talc]]), giving hydrogen some lithophile character.

Because all atmophile elements are either gases or form volatile hydrides, atmophile elements are strongly depleted on Earth as a whole relative to their solar abundances owing to losses from the atmosphere during the [[formation of the Earth]]. The heavier noble gases ([[krypton]], [[xenon]]) are the rarest stable elements on Earth. (In fact they, along with [[neon]], were all first isolated and described by [[William Ramsay]] and [[Morris Travers]] and assistants, who gave them names with Ancient Greek derivations of 'hidden', 'stranger', and 'new', respectively.)

[[Argon]] is the exception among the noble gases: it is the third-most abundant component of [[Earth's atmosphere|Earth's present-day atmosphere]] after nitrogen and oxygen, comprising {{approx|1%}}. [[Argon-40]] is a stable [[daughter nuclide|daughter]] of radioactive potassium-40, and argon is heavy enough to be gravitationally captured by the post-accretion Earth, so while the proto-Earth's primordial argon was mostly driven off, this [[radiogenic]] argon has accumulated over geologic time. This makes Earth's argon abundance substantially different from cosmic abundance ratios for argon, being enormously enriched in {{simple nuclide|Ar|40}}, while {{simple nuclide|Ar|36}} predominates cosmically.