A compound is two or more elements that are chemically combined.

The table below shows some common compounds.

CompoundFormulaElements present
waterH2Ohydrogen, oxygen
carbon monoxideCOcarbon, oxygen
carbon dioxideCO2carbon, oxygen
sulfur dioxideSO2sulfur, oxygen
sulfur trioxideSO3sulfur, oxygen
nitrogen monoxideNOnitrogen, oxygen
nitrogen dioxideNO2nitrogen, oxygen
ammoniaNH3nitrogen, hydrogen
hydrochloric acidHClhydrogen, chlorine
nitric acidHNO3hydrogen, nitrogen, oxygen
sulfuric acidH2SO4hydrogen, sulfur, oxygen