Equal masses, equal counts
Now the most surprising fact in the chapter. Weigh out the relative atomic mass in grams and, whichever element it is, you have the same number of atoms.
When a mass in grams equal to the relative atomic mass of any element is taken, whatever the element is, the number of atoms in it is one and the same. That number is 6.022 × 1023.
| Element | Ar | Mass taken | Number of atoms |
|---|---|---|---|
| Hydrogen (H) | 1 | 1 g | 6.022 × 1023 |
| Carbon (C) | 12 | 12 g | 6.022 × 1023 |
| Magnesium (Mg) | 24 | 24 g | 6.022 × 1023 |
| Chlorine (Cl) | 35.5 | 35.5 g | 6.022 × 1023 |
| Silver (Ag) | 108 | 108 g | 6.022 × 1023 |
It should not be a surprise
A silver atom is 108 times as heavy as a hydrogen atom. So to end up with the same number of atoms you must weigh out 108 times as much silver — 108 g instead of 1 g. It is the very way relative atomic masses are defined that makes this happen.
Counting by weighing
Atoms are far too small to count. Grams can be weighed. What this idea does is turn a balance into a counting instrument, and the rest of the chapter is built on it.