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A molecule is the smallest particle of a substance that exists independently. Molecules of most elements are made up of only one of atom of that element. Oxygen, along with nitrogen, hydrogen, and chlorine are made up of two atoms. Look at the model of oxygen above.The two balls represents the two oxygen molecules. molecule is the smallest particle of a substance that exists independently. Molecules of most elements are made up of only one of atom of that element. Oxygen, along with nitrogen, hydrogen, and chlorine are made up of two atoms. Look at the model of oxygen above.
Most of the substances around us consist of molecules and are called compounds of various elements. Molecules are the smallest particle of a compound that has all the chemical properties of that compound. They are made up of two or more atoms, either of the same element or of two or more different elements.olecules and compounds contain their constituent elements in specific proportions that are characteristic of the compound. For example, water (H 2 O), a well known and simple compound, contains hydrogen and oxygen at a ratio of 2 to 1.