Chemistry

Atoms and Molecules


How Do Atoms Exist


The atoms of only a few elements called noble gases (such as helium neon, argon and krypton, etc.) are chemically unreactive and exist in the free state (as single atoms).Atoms of most of the elements are chemically very reactive and do not exist in the free state (as single atoms).Atoms usually exist in two ways :
1.in the form of molecules,and
2.in the form of ions.
When atoms form molecules or ions, they become stable (because in doing so they acquire the stable electron arrangements of noble gases). The molecules and ions stick together in large numbers to form the various types of matter around us. Though we cannot see the individual molecules or ions with our eyes,we can, however, see the various substances which are a big collection of molecules or ions. For example,we cannot see the individual iodine molecules (12) with our eyes because they are very,very small but we can see iodine crystal as a violet coloured solid because it is a collection of millions and millions of iodine molecules held together. Similarly, we cannot see the individual sodium ions (Na+) and chloride ions (Cl-) but we can see the sodium chloride compound (common salt) as a white powder because it is formed by the collection of millions and millions of sodium ions and chloride ions.We will now discuss the molecules and ions in detail,one by one.

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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. 2. A Negatively Charged Ion is Known as Anion
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11. As an example, let us give the significance of the formula H2O
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12. Molecules
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13. Chemical Formulae
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14. Molecular Mass
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15. Molecules of Compounds
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16. Atoms, Molecules and Ions
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17. Explanation of the Law of Conservation of Mass
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18. Some Ionic Compounds
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19. Atoms
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20. Mole of Molecules
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21. Formula Mass
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22. 1. A Positively Charged Ion is Known as Cation
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23. Formulae of Elements
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24. 1. Molecules of Elements
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25. Simple Ions and Compound Ions (Polyatomic Ions)
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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. How Do Atoms Exist
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43. Atoms And Molecules
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44. Problems Based On Moles Of Molecules
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45. Writing Of Formulae Of Ionic Compounds
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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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