H2S/Hydrogen & Sulfur/ 2, 1
HCl/Hydrogen & Chlorine/ 1,1
NaCl/Sodium & Chlorine/ 1,1
CaCO3/ Calcium, Carbon & Oxygen/ 1,1,3
The molecular formulas as: H2S, HCl, etc. are indeed easy to read.
Just remember:
1. These formulas include the atomic symbols of each element that conforms the molecule. The atomic symbols are composed by one (e.g. H, S, C, O) or two (e.g. Na, Cl, Ca) latin letters and the first one will be always capitalized.
2. Following the atomic symbol could be a number which indicates the number of atoms of that element in the molecule. When no number appears after the symbol, it is assumed that there is only one atom of that element in the molecule.