A grain of sand has a lot of atoms, and we can calculate the number of atoms in it using Avogadro’s number. This number is equivalent to the number of molecules found in a grain of sand. This number is found in solids with a volume of interest. The answer is 50 million. So, the next question to ask yourself is, “How many molecules are in a grain of sand?”
Scientists estimate that there are 7.5 sextillion atoms in a grain of sand. That’s 75 followed by 17 zeros. So, if we were to compare the number of atoms in a grain of sand with the number of stars in the universe, we’d be looking at about 70 million atoms. However, if we want to be more precise, we’d have to assume that a grain of sand has a similar number of atoms as a star.
There are more atoms than you might think. A grain of sand contains about a cubic centimetre, which is equivalent to a mole. A mole is 6×1023 atoms, while a cubic centimetre has about a million atoms. That’s a lot more than a grain of sand, which weighs a mere 0.03 grams.
To compare the mass of a speck of sand and a million atoms, a teaspoon of water contains 2×1023 atoms. That’s equivalent to about seventy grains of sand, or about 70 grams of sand. If you compare that to the mass of a star, you can see that an atom is roughly one centimeter in size.
Since water makes up less than 0.03% of the earth’s mass, it is not possible to estimate the density of a grain of sand as the balance between water and earth’s average density. Scientific judgment does not only involve complex calculations, but it also involves a few simple sanity checks. A grain of sand actually contains around 50 million atoms that are only separated by a couple Angstroms.
A grain of sand is about 1 millimeter in diameter, and a typical apple needs to be magnified a hundred million times before you can see an atom. If you can visualize this, then you’ll understand why an apple’s size is so small. In addition to its size, atoms are also tiny, but they’re still a few nanometers wide.