A chemical compound is a substance that is made of two or more elements that are chemically bonded together in a fixed ratio. The formula of a compound consists of the symbols of the elements it contains with subscripts representing their proportions. For example, water, which has the formula H2O, has two hydrogen atoms and one oxygen atom per molecule.
Here are some examples of chemical compounds and their formulas:
`CO_2` , carbon dioxide
`C_6H_12O_6` , glucose
`C_12H_22O_11` , sucrose (white sugar)
`NaCl` , sodium chloride (table salt)
`CH_3COOH`, acetic acid (vinegar)
`C_2H_5OH` , ethanol
`C_8H_18` , octane (gasoline)
`CaCO_3` , calcium carbonate (limestone)
`NaClO` , sodium hypochlorite (bleach)
`NaHCO_3` , sodium hydrogen carbonate (baking soda)
`MgSO_4` , magnesium sulfate (Epsom salt)
`NaOH` , sodium hydroxide (lye)
A compound can exist as individual particles called molecules or as a crystal lattice of repeating formula units. For example, carbon dioxide, a molecular compound, consists of molecules that each contain one carbon and two oxygen atoms. Alternatively, sodium chloride, an ionic compound, exists as a crystal lattice of many sodium and chloride ions in a 1:1 ratio.