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Medicine LibreTexts

1.3: Compounds and Molecules

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  • A molecule is formed when two or more atoms join together. A compound is formed when two or more different elements combine in a fixed ratio by mass. Note that some atoms are never found alone. For example oxygen is always found as molecules of 2 oxygen atoms (represented as O2).

    The table below gives some common compounds.

    Compound Symbol
    Calcium carbonate CaCO3
    Carbon dioxide CO2
    Copper sulphate CuSO4
    Glucose C6H12O6
    Hydrochloric acid HCl
    Sodium bicarbonate (baking soda) NaHCO3
    Sodium chloride (table salt) NaCl
    Sodium hydroxide NaOH
    Water H2O


    • Ruth Lawson (Otago Polytechnic; Dunedin, New Zealand)