Chemistry

Structure of the Atom


Isobars


We have just studied isotopes which are atoms of the same element having the same atomic number but different mass numbers.It is, however, also possible that in some cases, the atoms of different elements having different atomic numbers may have the same mass number. Such atoms are called isobars. We can now say that:Isobars are the atoms of different elements having different atomic numbers but the same mass number (or same atomic mass).Isobars have different number of protons in their nuclei but the total number of nucleons (protons + neutrons) in them is the same. An example of isobars is argon,= 4018Ar and calcium = 4020Ca.This is because argon and calcium are atoms of different elements having different atomic numbers of 18 and 20 respectively but the same mass number of 40. The complete nuclear composition of the isobars = 4018Ar and = 4020Ca is given below :
IsobarProtonsNeutronsMass number
= 4018Ar
= 4020Ca
18
20
22
20
18+22=40
20+20=40

Here is another example of isobars.The radioactive sodium,= 2411Na,and magnesium = 2412Mg,are isobars.This is because radioactive sodium and magnesium are different elements having different atomic numbers of 11 and 12 respectively but the same mass number of 24.
In order to find out isobars from among a number of given species, we should look at their atomic numbers and mass numbers. The atomic species having different atomic numbers but same mass number will be isobars. We will now solve some problems based on isobars.
Sample Problem 1. Which two of the following atomic species are isotopes of each other and which two are isobars ?
= 23190Z,= 23091Z,= 23088Z,= 23390Z
Solution (a).The isotopes of an element have the same atomic number but different mass numbers.The lower figures in the above given symbols indicate the atomic numbers.Now,in this case there are two atoms having the same atomic number of 90. So, the two isotopes will be := 23190Z and = 23390Z
(b) The isobars have different atomic numbers but same mass numbers. The upper figures in the given symbols indicate the mass numbers. In this case there are two atoms having the same mass number of 230.So, the two isobars will be :
= 23091Z and = 23088Z
Sample Problem 2.Write the electronic configurations of any one pair of (a) isotopes,and (b) isobars.
Solution, (a) A pair of isotopes of chlorine is = 3517Cl and = 3717Cl.The atomic number of both the isotopes is the same, 17. So, the electronic configuration of both these isotopes will be 2,8,7.
(b) A pair of isobars is = 4018Ar and = 4020Ca.The atomic number of argon (Ar) is 18, so its electronic configuration will be 2,8,8. The atomic number of calcium (Ca) is 20, so its electronic configuration will be 2, 8, 8, 2.
We are now in a position to answer the following questions :

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Notes


Structure of the Atom - Notes
1. Drawback of Rutherford’s Model of the Atom
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2. Rutherford’s Experiment - Discovery of Nucleus
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3. For the symbols H, D and T,tabulate three sub-atomic particles found in each of them.
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4. Structure of The Atom - Study Points
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5. 4.Isotopes of Neon.
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6. Radioactive Isotopes
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7. 3.Isotopes of Oxygen.
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8. Characteristics of a Neutron
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9. Nucleus
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10. Arrangement Of Electrons In The Atoms
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11. (d) Covalency of Nitrogen
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12. Limitations of Rutherford's model of the atom
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13. Characteristics of an Electron
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14. (b) Valency of Magnesium
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15. How to learn naming Chemical Formulae?
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16. All about Names of the Chemical Elements
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17. 1. Isotopes of Hydrogen.
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18. Mass Number
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19. Characteristics of a Proton
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20. (d) Valency of Chlorine
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21. Comparison between Proton, Neutron and Electron
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22. Electronic Configurations of First 20 Elements
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23. Discovery of Neutron
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24. Thomson's Model Of The Atom
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25. (e) Valency of Oxygen
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26. Rules for writing of distribution of electrons in various shells for the first 18 elements
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27. Isotopes
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28. 2.Covalency
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29. Covalency of Oxygen
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30. (a) Covalency of Hydrogen
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31. Bohr's Model Of The Atom
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32. Discovery Of Electron
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33. Rutherford's Model Of The Atom
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34. (a) Valency of Sodium
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35. Atomic Number
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36. 2.Isotopes of Carbon.
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37. The Physical Properties of the Isotopes of an Element are Different
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38. Charged Particles in Matter
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39. Discovery of Proton
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40. All the Isotopes of an Element Have Identical Chemical Properties
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41. Valaency Of Elements
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42. Relationship Between Mass Number and Atomic Number
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43. (f) Valency of Nitrogen
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44. Electronic Configurations of Noble Gases (or Inert Gases)
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45. Valaence Electrons (Or Valancy Electrons)
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46. Covalency of Chlorine
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47. Reason for the Fractional Atomic Masses of Elements
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48. Cause of Chemical Combination
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49. Relation Between Valency and Valence Electrons
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50. Covalency of Carbon
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