Chemistry

Atoms and Molecules


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 (H2O) 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 H2O = Mass of 2H atoms + Mass of O atom
= 2 + 16
= 18 u
Thus, the molecular mass of water (H2O) 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. Drawbacks of Dalton’s Atomic Theory
Show Notes
2. Monovalent Cations (Cations Having a Valency of 1+)
Show Notes
3. Dalton’s Symbols of Elements
Show Notes
4. Divalent Cations (Cations Having a Valency of 2+)
Show Notes
5. Trivalent Cations (Cations Having a Valency of 3+)
Show Notes
6. Formulae of Some Molecular Compounds
Show Notes
7. An Important Discussion
Show Notes
8. Molecular Formulae of Some Common Elements
Show Notes
9. an example, let us give the significance of symbol C
Show Notes
10. Chemical Formulae
Show Notes
11. As an example, let us give the significance of the formula H2O
Show Notes
12. 2. A Negatively Charged Ion is Known as Anion
Show Notes
13. Molecules
Show Notes
14. Molecular Mass
Show Notes
15. Molecules of Compounds
Show Notes
16. Explanation of the Law of Conservation of Mass
Show Notes
17. Some Ionic Compounds
Show Notes
18. Atoms, Molecules and Ions
Show Notes
19. Atoms
Show Notes
20. Formula Mass
Show Notes
21. Mole of Molecules
Show Notes
22. Formulae of Elements
Show Notes
23. 1. A Positively Charged Ion is Known as Cation
Show Notes
24. Simple Ions and Compound Ions (Polyatomic Ions)
Show Notes
25. 1. Molecules of Elements
Show Notes
26. Symbols of Elements
Show Notes
27. Gram Atomic Mass And Gram Molecular Mass
Show Notes
28. John Dalton
Show Notes
29. Mole of Atoms
Show Notes
30. Formulae of Compounds
Show Notes
31. Ions
Show Notes
32. Explanation of the Law of Constant Proportions
Show Notes
33. Dalton's Atomic Theory
Show Notes
34. Significance of the Formula of a Substance
Show Notes
35. Some Common Ions
Show Notes
36. Molecular Masses of Some Common Elements
Show Notes
37. Ionic Compounds
Show Notes
38. Laws Of Chemical Combination
Show Notes
39. Calculation of Molecular Mass
Show Notes
40. Formula Unit of Ionic Compounds
Show Notes
41. Divalent Anions (Anions Having a Valency of 2-)
Show Notes
42. Atoms And Molecules
Show Notes
43. How Do Atoms Exist
Show Notes
44. Writing Of Formulae Of Ionic Compounds
Show Notes
45. Problems Based On Moles Of Molecules
Show Notes
46. Experiment to Verify Law of Conservation of Mass
Show Notes
47. Gram Molecular Mass
Show Notes
48. Gram Atomic Mass
Show Notes
49. Laws Of Conservation of Mass
Show Notes
50. Atomic Radii of Some Common Elements
Show Notes