Calculation of Molecular Mass
If the molecular formula of a substance is known, its molecular mass can be calculated, because the molecular mass is equal to sum of the atomic masses of all the atoms present in one molecule of the substance. For example, one molecule of water () contains 2 atoms of hydrogen and 1 atom of oxygen.So,the molecular mass of water will be equal to the sum of the masses of 2 hydrogen atoms and 1 oxygen atom. Knowing that the atomic mass of hydrogen is 1 u and that of oxygen is 16 u, the molecular mass of water can be calculated as follows :
Mass of H atom = 1 u
Mass of 2H atoms = 2x1
= 2 u
Mass of O atom = 16 u
Now, Molecular mass of = Mass of 2H atoms + Mass of O atom
= 2 + 16
= 18 u
Thus, the molecular mass of water () is 18 u.
In the case of ionic compounds like sodium chloride which consist of ions (and not molecules) the term formula mass is sometimes used in place of molecular mass. The molecular masses of some common elements, which exist as molecules, are given below :
Notes
Atoms and Molecules - Notes
1. Monovalent Cations (Cations Having a Valency of 1+)
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3. Divalent Cations (Cations Having a Valency of 2+)
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4. Trivalent Cations (Cations Having a Valency of 3+)
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6. an example, let us give the significance of symbol C
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7. Formulae of Some Molecular Compounds
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10. Simple Ions and Compound Ions (Polyatomic Ions)
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11. Explanation of the Law of Conservation of Mass
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12. Molecular Formulae of Some Common Elements
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13. 2. A Negatively Charged Ion is Known as Anion
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14. As an example, let us give the significance of the formula H
2O
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20. Gram Atomic Mass And Gram Molecular Mass
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28. 1. A Positively Charged Ion is Known as Cation
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34. Divalent Anions (Anions Having a Valency of 2-)
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36. Molecular Masses of Some Common Elements
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38. Significance of the Formula of a Substance
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39. Explanation of the Law of Constant Proportions
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42. Symbols Derived from Latin Names of the Elements
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45. Valencies of Some Common Metal Elements Valencies of Some Common Non-Metal Elements
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46. Atomic Masses of Some Common Elements
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48. Writing Of Formulae Of Molecular Compounds
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50. Writing Of Formulae Of Ionic Compounds
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