Nucleus
The nucleus is a small positively charged part at the centre of an atom.The nucleus contains all the protons and neutrons, therefore,almost the entire mass of an atom is concentrated in the nucleus (the electrons, which are outside the nucleus, have negligible mass). The positive charge on the nucleus is due to the presence of protons in it. The number of protons in the nucleus determines the number of positive charges on the nucleus. The neutrons which are also present in the nucleus have no charge, they are neutral.Protons and neutrons taken together are known as nucleons (because they are present in the nucleus).The volume of the nucleus of an atom is very small as compared to the volume of the extranuclear part of the atom.The existence of positively charged nucleus in an atom was shown by the alpha particle scattering experiment of Rutherford.
Please note that when Rutherford put forward his nuclear model of atom in 1911, even then only electrons and protons were known to be present in the atom.This is because neutron was discovered much later in 1932. So,the original model of an atom given by Rutherford contained only protons in the nucleus. It contained no neutrons. Rutherford's model of the atom was improved later on by including neutrons in the nucleus.We will study this improved model of atom now.
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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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5. Structure of The Atom - Study Points
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10. Arrangement Of Electrons In The Atoms
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13. Limitations of Rutherford's model of the atom
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15. All about Names of the Chemical Elements
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17. How to learn naming Chemical Formulae?
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20. Comparison between Proton, Neutron and Electron
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21. Electronic Configurations of First 20 Elements
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26. Rules for writing of distribution of electrons in various shells for the first 18 elements
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36. The Physical Properties of the Isotopes of an Element are Different
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39. All the Isotopes of an Element Have Identical Chemical Properties
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42. Relationship Between Mass Number and Atomic Number
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44. Valaence Electrons (Or Valancy Electrons)
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45. Electronic Configurations of Noble Gases (or Inert Gases)
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48. Reason for the Fractional Atomic Masses of Elements
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49. Applications of Radioactive Isotopes
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50. Relation Between Valency and Valence Electrons
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