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

1 Answer
Sep 2, 2017

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.eduhttp://climate.ncsu.edu