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. 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. Explanation of the Law of Conservation of Mass
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10. Molecular Formulae of Some Common Elements
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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. Simple Ions and Compound Ions (Polyatomic Ions)
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15. Molecules of Compounds
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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. Modern Symbols of Elements
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44. Atomic Mass Of An Element
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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. Writing Of Formulae Of Ionic Compounds
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