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

1 Answer
Sep 2, 2017

Answer:

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

  • #"N"_2#

  • #"O"_2#

  • #"F"_2#

  • #"Cl"_2#

  • #"Br"_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# (#78.0%#)

  • #"O"_2# (#21.0%#)

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

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

http://climate.ncsu.edu