The chemical formula of water is H2O.
H2o
ye
An atom is what makes up chemical formulae. Just look at the periodic table -- those are your chemical formulae for atoms. Can be from H to Uuo.
H2
HCl
KOH
H2s2o8
NaHCO3
AgNO3
It is butane.
Not every chemical formula requires subscript. For example table salt is NaCl, sodium chloride. No subscript. But most chemical formulae do require subscript, such as water, H2O.
chemical work using chemical formulae and chemical compounds
An identification of the atoms is a molecule (APEX)