This number can be measured experimentally by several independent
methods, using gases, liquids, and crystals, and has been found
to have the value
N = 602, 209, 430, 000, 000, 000, 000, 000 N = 6.022 x 10
molecules
As an illustration of how many molecules there are in one mole,
if each molecule were represented by an ordinary glass marble, and
these marbles were packed as closely together as possible, one mole
of marbles would cover the entire United States with a layer seventy
miles deep!
All these molecules are contained in only 2.016 grams of hydrogen
gas (a balloon 35 cm in diameter), 18.015 grams of water (half of
a one ounce shot glass), or a cube of rock salt 3 cm on a side.
molecules 
