How to find how many atoms are in a formula such as H20

2 hydrogens, one oxygen in a molecule

so three atoms per molecule
a mol is 6*10^23 molecules
so
18 * 10^23 atoms per molecule
a mol weighs 2+16 = 18 grams
so
(6/18) * 10^23 molecules per gram

I mean (6/18)*10^23 atoms/gram

Thank you!

You are welcome.

To find how many atoms are in a formula such as H2O (water), you need to consider the subscripts in the chemical formula. The subscript indicates the number of atoms of that element present in the molecule.

For H2O, the subscript of 2 next to H means that there are two hydrogen atoms. The subscript 1 is often omitted. So, we have 2 hydrogen atoms. For oxygen, there is no subscript, which implies that there is only one oxygen atom.

Hence, in H2O, there are 2 hydrogen atoms and 1 oxygen atom, totaling 3 atoms in total.