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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.
Answers. 1  Elements are the simpliest form of complete matter, for example a single hydrogen (H) atom. When atoms combine and share electrons, they form compounds or molecules, such as H2O, water. When many very complex compounds combine in a very unique manner within a cell, they form the necessary parts of that cell organs or organelles.