What is Amount of substance and mole?

Example 25.10 (One mole of carbon atoms)

An atom of carbon-12 has a mass of about $12 \times 1.67 \times 10^{-27}\,\mathrm{kg} = 2.00 \times 10^{-26}\,\mathrm{kg}$. One mole of them has a mass of

The mole has been chosen so that the molar mass of an atom, in grams per mole, is close to its mass number: about $1\,\mathrm{g}/\mathrm{mol}$ for hydrogen, $12\,\mathrm{g}/\mathrm{mol}$ for carbon, $16\,\mathrm{g}/\mathrm{mol}$ for oxygen.

Example 25.17 (A mole on the bench)

One mole of water is $18.0\,\mathrm{g}$, about a tablespoon. One mole of salt, $58.5\,\mathrm{g}$, is a small heap; one mole of sugar, $342.0\,\mathrm{g}$, fills a mug; one mole of iron, $55.8\,\mathrm{g}$, is a cube a little under $2\,\mathrm{cm}$ across. All four hold the same number of entities: the molecules of sugar are simply much heavier than those of water, and the atoms of iron are packed much more tightly.