What can you learn about a compound from its chemical formula

From the chemical formula of a compound you can learn about its composition:

Also, with the ratios and the atomic masses of each kind of atom, you can obtain the mass composition (%) of the compound.

Explanation:

Using indexes (subscripts), the chemical formula of a compound shows  the elements (kind of atoms) in the compound and the relative proportions of those elements.

The following example will show you how you learn that information from the chemical formula.

A very familiar compound is water and its chemical formula (also very familiar) is H₂O.

From that, you learn that water (a chemical compound):

        * hydrogen, H: 2 × 1.008 g/ mol = 2.016 g/,ol

        * oxygen, O: 1 × 15.999 g/mol = 15.999 g/mol

        * Molar mass of water: 2.016 g/mol + 15.999 g/mol = 18.015 g/ mol

        * H: (2.016 g/mol / 18.015 g/mol) × 100 = 11.19%

        * O: (15.999 g/mol / 18.015 g/mol) × 100 = 88.81%

there is none because earth is stationary and flat.