Thomson’s Atomic Model
Thomson’s Atomic Model :
- After the confirmation of the presence of electron and proton in the atom, Thomson in 1898 said that the atom is a positively charged sphere in which are embedded the negatively charged electrons. He compared it with the dessert “Plum pudding” in which dry fruits are present scattered within the cake. We can understand it by using the example of water melon. The fleshy part of which is the positive region and the seeds present in it may be considered the electron. This model was named as the ‘ Plum Pudding Model ‘.
- Shortly, after some time, this model was rejected as it could not interpret the alpha particle dispersion experiments done by Rutherford.
Important Points :-
- The basic particles of atom are electron, proton and neutron.
- The negatively charged particles in the atom are electrons.
- The numeric value of the charge on electron and proton is the same but their sign is opposite.
- James Chadwick discovered neutrons.
- There are 6.022×1023 particles in one mole. This is known as the Avogadro number.
- The NTP volume of 1 mole of a gas is 22.4 litres.
- The formula to determine the maximum number of electrons in a shell is 2n2 .
- When the atomic number is the same but mass number is different they are known as Isotopes.
- Isobars are elements having different atomic number and the same mass number.
- There are three isotopes of hydrogen, Protium, Deutirium and Tritium.
Atomic Structure Important Questions-Answers
1. The Plum Pudding Model of atom was given by:
(a) Neil Bohr
(b) Thomson
(c) Ernest Rutherford
(d) Goldstein
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Answer⇒ { B}
2. The discoverer of neutron was :
(a) C.V. Raman
(b) Rutherford
(c) J.J. Thomson
(d) James Chadwick
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Answer ⇒ { D}
3. The size of atom is :
(a) 10-6 cm
(b) 10-15 cm
(c) 10-2 cm
(d) 10-8 cm
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Answer ⇒ {D }
4. The number of neutrons in the Deutirium Isotope of hydrogen is /are :
(a) one
(b) Two
(c) Three
(d) Not even one
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Answer ⇒ {A }