Amolecule of one atom of carbon and two atoms of oxygen would be written

For this case we can refer to carbon dioxide.

The way to write the chemical formula in this case is:

CO2

This means that the element this formed by:

1) One Carbon atom

2) Two oxygen atoms

Carbon dioxide is a colorless gas vital for life on earth.

A molecule of one atom of carbon and two atoms of oxygen would be written CO2.