What gases in Earth's atmosphere would you expect to find as molecules and which as individual atoms?

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What gases in Earth's atmosphere would you expect to find as molecules and which as individual atoms?

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Answer 1 · 2017-09-02T14:31:04

The only somewhat significant gases that occur as pure elements will be $Ar$ $"Ar"$ and trace amounts of $Ne$ $"Ne"$ and $He$ $"He"$ .

All other gases that contribute a significant amount to the atmosphere's composition will be molecules.

Explanation:

Well, recall that there are seven elements that occur naturally diatomic, which means they occur in nature as two-atom molecules. These seven are

$H_{2}$ $"H"_2$
$N_{2}$ $"N"_2$
$O_{2}$ $"O"_2$
$F_{2}$ $"F"_2$
${Cl}_{2}$ $"Cl"_2$
${Br}_{2}$ $"Br"_2$
$I_{2}$ $"I"_2$

Of these seven, the first five are gaseous at standard conditions, and of those five, there are only two that exist to a significant extent in Earth's atmosphere:

$N_{2}$ $"N"_2$ ( $78.0 %$ $78.0%$ )
$O_{2}$ $"O"_2$ ( $21.0 %$ $21.0%$ )

The remaining $1 %$ $1%$ is taken up mostly by argon, $Ar$ $"Ar"$ ( $0.9 %$ $0.9%$ ), and the rest are trace gases, such as ${CO}_{2}$ $"CO"_2$ ( $0.093 %$ $0.093%$ ), $Ne$ $"Ne"$ (monatomic, $0.0047 %$ $0.0047%$ ), $He$ $"He"$ (monatomic, $0.0013 %$ $0.0013%$ ), and others such as ${CH}_{4}$ $"CH"_4$ (methane), $N_{2} O$ $"N"_2"O"$ (nitrous oxide), and $O_{3}$ $"O"_3$ (ozone).

Below is a neat little pie chart of gaseous abundance in Earth's atmosphere:

![http://climate.ncsu.edu](http://climate.ncsu.edu/secc_edu/images/AtmConcentration.bmp)

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What gases in Earth's atmosphere would you expect to find as molecules and which as individual atoms?

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