Chemistry

Atoms and Molecules


Atoms


Just as all the houses are made up of bricks, in the same way, all the matter is made up of atoms. Thus,atoms are the building blocks of all the matter around us. In chemistry, atom is defined as follows : An atom is the smallest particle of an element that can take part in a chemical reaction.Atoms of most of the elements are very reactive and do not exist in the free state (as single atoms). They exist in combination with the atoms of the same element or another element. There are as many kinds of atoms as are elements.
Atoms are very, very small in size.An idea of the extremely small size of atoms can be had from the fact that 35,000,000 copper atoms arranged end to end in a line would cover a distance of about 1 centimetre ! The size of an atom is indicated by its radius which is called 'atomic radius (radius of atom). Atomic radius is measured in 'nanometres'(which is a very, very small unit of measuring length).The symbol of a nanometre is nm.
1 nanometre = 1109
or 1 nm = 1109
or 1 nm = 110-9
Hydrogen atom is the smallest atom of all.The atomic radius of a hydrogen atom is 0.037 nanometre (or 0.037 nm). If we express the radius of a hydrogen atom in metres,it will be 0.037 x 110-9metre which means 0.000000000037 metre ! It is really very, very small. The atomic radii of some of the common elements are given below (Please note that 'radii' is the plural of radius).

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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. Formulae of Some Molecular Compounds
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7. an example, let us give the significance of symbol C
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8. An Important Discussion
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9. Chemical Formulae
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10. Molecular Formulae of Some Common Elements
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11. As an example, let us give the significance of the formula H2O
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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. Explanation of the Law of Conservation of Mass
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15. Molecules of Compounds
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16. Molecular Mass
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17. Atoms
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18. Some Ionic Compounds
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19. Atoms, Molecules and Ions
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20. Formulae of Elements
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21. Simple Ions and Compound Ions (Polyatomic Ions)
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22. Formulae of Compounds
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23. Formula Mass
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24. Symbols of Elements
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25. 1. A Positively Charged Ion is Known as Cation
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26. 1. Molecules of Elements
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27. Mole of Molecules
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28. Gram Atomic Mass And Gram Molecular Mass
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29. Mole of Atoms
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30. John Dalton
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31. Ions
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32. Dalton's Atomic Theory
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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. Writing Of Formulae Of Ionic Compounds
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44. How Do Atoms Exist
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45. Gram Molecular Mass
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46. Problems Based On Moles Of Molecules
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47. Laws Of Conservation of Mass
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48. Experiment to Verify Law of Conservation of Mass
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49. Problems Based On Moles Of Atoms
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50. Writing Of Formulae Of Molecular Compounds
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