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Atomic and Molecular Weights - Atomic and Molecular Weights...

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Atomic and Molecular Weights The subscripts in chemical formulas, and the coefficients in chemical equations represent exact quantities. H 2 O, for example, indicates that a water molecule comprises exactly two atoms of hydrogen and one atom of oxygen. The following equation: not only tells us that propane reacts with oxygen to produce carbon dioxide and water, but that 1 molecule of propane reacts with 5 molecules of oxygen to produce 3 molecules of carbon dioxide and 4 molecules of water. Since counting individual atoms or molecules is a little difficult, quantitative aspects of chemistry rely on knowing the masses of the compounds involved. The atomic mass scale Atoms of different elements have different masses . Early work on the separation of water into its constituent elements (hydrogen and oxygen) indicated that 100 grams of water contained 11.1 grams of hydrogen and 88.9 grams of oxygen: 100 grams Water -> 11.1 grams Hydrogen + 88.9 grams Oxygen Later, scientists discovered that water was composed of two atoms
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