ATOMS IN THE AIR
The Arithmetic
(a) Weight of the atmosphere in pounds1 = 1.16 x 1019
(b) Moles in one pound of air2 = 15.75
(c) Avogadro number3 = 6.02 x 1023
(d) Molecules in one pound of air = (b) x (c)4 = 9.48 x 1024
(d') Atoms in one pound of air5 = (d) x 2 = 1.9 x 1025
Atoms in the atmosphere = (d') x (a) = 1.16 x 1.9 x 1019 x 1025 = 2.2 x 1044
Atoms in one cubic foot of air - At standard conditions one pound of air occupies about 12.4 cubic feet. So, one cubic foot of air contains 1.5 x 1024 atoms [(d') divided by 12.4].
Notes for this calculation
1 The calculation is made under "Prove it" of 1018.
2 For an explanation of the term "mole," see "Prove it" under 1024.
Air consists of about 80% nitrogen and 20% oxygen. A molecule of nitrogen, which consists of two atoms of nitrogen, has an atomic weight of 28. Similarly, the atomic weight of a molecule of oxygen, which consists of two atoms of oxygen, is 32.
One mole of nitrogen weights 28 grams, while one mole of oxygen weighs 32 grams. Each mole contains an Avogadro number of molecules. Thus, 144 grams of air contains four moles of nitrogen and one mole of oxygen (4x28 + 1x32 = 144).
There are about 454 grams in one pound.
So one pound of air contains about 15.75 moles of nitrogen and oxygen combined (454/144 times 5).
3 For an explanation of "Avogadro's number," see "Prove it" under 1024.
4For an explanation of how to multiply big numbers written in scientific notation, see this topic under "About Big Numbers."
5Both oxygen and nitrogen molecules consist of two atoms.