(a) Describe the Rutherford's model of an atom. State one drawback of Rutherford's model of the atom.(b) The mass number of an element is 23 and it contains 11 electrons. What is the number of protons and neutrons in it? What is the atomic number of the element?
(a) Rutherford conducted an experiment with a gold foil bombarded with fast-moving alpha particles.
- A gold foil with 1000 atoms thick has been taken
- Helium ions are used to bombard the gold foil.
- It was expected that the alpha particles would be deflected by the subatomic particles in the gold atoms. Since the alpha particles were much heavier than the protons, he did not expect to see large deflections.
Alpha particle scattering experiment output was unexpected
Observations:
- Most of the fast-moving alpha particles passed through the gold foil
- Some of the alpha particles were deflected by the foil by small angles.
- 12000 particles appeared to rebound.
Conclusion:
a) Most of the atom is hollow.
b) The small angle deviation of the alpha particles confirms the presence of a positively charged center called the nucleus.
c) The nucleus of an atom is solid as the ray returns on its path and is very small in size.
Drawbacks of this model: He failed to explain the stability of the atom.
(b) Mass no. = 23
No. of electrons = 11
Hence, no. of protons = 11
No. of neutrons = 23 - 11 = 12
Atomic no. = 11
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