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