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. Divalent Cations (Cations Having a Valency of 2+)
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4. Dalton’s Symbols of Elements
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5. 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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8. Molecular Formulae of Some Common Elements
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9. Chemical Formulae
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10. An Important Discussion
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11. 2. A Negatively Charged Ion is Known as Anion
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12. Molecules
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13. Explanation of the Law of Conservation of Mass
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14. As an example, let us give the significance of the formula H2O
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15. Atoms
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16. Molecular Mass
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17. Molecules of Compounds
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18. Some Ionic Compounds
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19. Formulae of Elements
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20. Simple Ions and Compound Ions (Polyatomic Ions)
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21. Symbols of Elements
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22. Atoms, Molecules and Ions
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23. Formula Mass
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24. Formulae of Compounds
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25. 1. A Positively Charged Ion is Known as Cation
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26. Gram Atomic Mass And Gram Molecular Mass
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27. Mole of Atoms
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28. 1. Molecules of Elements
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29. Mole of Molecules
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30. Ions
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31. Dalton's Atomic Theory
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32. John Dalton
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33. Explanation of the Law of Constant Proportions
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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. Laws Of Chemical Combination
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38. Divalent Anions (Anions Having a Valency of 2-)
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39. Calculation of Molecular Mass
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40. Ionic Compounds
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41. Formula Unit of Ionic Compounds
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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 Atoms
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46. Symbols Derived from Latin Names of the Elements
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47. Gram Molecular Mass
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48. Laws Of Conservation of Mass
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49. Writing Of Formulae Of Molecular Compounds
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50. Experiment to Verify Law of Conservation of Mass
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