Chemistry

Atoms and Molecules


Formulae of Compounds


The chemical formula of a compound is a statement of its composition in which the chemical symbols tell us which elements are present and the subscripts (lower figures) tell us how many atoms of each element are present in one molecule of the compound.Water is a compound whose molecule contains 2 atoms of hydrogen and 1 atom of oxygen. So, the formula of water is H2O.In the formula H20, the symbol H2 indicates 2 atoms of hydrogen (and not a molecule of hydrogen),and O represents 1 atom of oxygen. The figure in front of a formula shows the number of molecules. For example,2H2O means 2 molecules of water.The figure 2 multiplies the whole formula H2O and not just the first element. That is, 2H2O contains 4 atoms of hydrogen and two atoms of oxygen. The chemical formulae of some common molecular compounds (which consist of molecules) and the elements present in them are given below.

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