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. 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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