Write down the drawback of Bohr's Atomic Model.
Write down the properties of Neutron.
Describe the structure of Ratherford atomic model.
Why Ratherford choose gold foil?
Answers
Answer
(a) Rutherford conducted experiment with a gold foil bombarded with fast moving alpha particles.
1. A gold foil with 1000 atoms thick has been taken
2. Helium ions are used to bombard the gold foil.
3. 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 expected to see large deflections.
Alpha particle scattering experiment output was unexpected
Observations:
a) Most of the fast-moving alpha particles passed through the gold foil
b) Some of the alpha particles were deflected by the foil by small angles.
c) 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 centre called 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:
1. He failed to explain the stability of the atom.
(b) Given: Mass no. = 23
No. of electrons = 11
Then, no. of protons = 11
No. of neutrons = 23 - 11 = 12
Atomic no. = 11
Answer
i) It is valid only for one electron atoms, eg: H, He
+
,Li
+2
,Na
+1
etc.
ii) Orbits were taken as circular but according to Sommerfiled these are elliptical.
iii) Intensity of spectral lies could not be explained.
iv) Nucleus was taken as stationary but it also rotates on its own axis.
v) It could not be explained the minute structure in spectrum line.
vi) This does not explain the Zeeman effect (splitting up of spectral lines in magnetic filed) and Stark effect (splitting up in electric filed)
vii) This does not explain the doublets in the spectrum of some of
Answer
(i) Neutrons are the constituent particles of all nuclei, except hydrogen.
(ii) They are neutral particles with no charge and mass slightly greater than that of protons. Hence, they are not deflected by electric and magnetic fields.
(iii) They are stable inside the nucleus. But outside the nucleus they are unstable. The free neutron decays with an emission of proton, electron and antineutrino, with half-life of 13 minutes.
0
n
1
→
1
H
1
+
−1
e
0
+
v
answer
The atom, as described by Ernest Rutherford, has a tiny, massive core called the nucleus. The nucleus has a positive charge. Electrons are particles with a negative charge. ... The empty space between the nucleus and the electrons takes up most of the volume of the atom.
answer
Ernest Rutherford was interested in knowing how the electrons are arranged within an atom. Rutherford designed an experiment for this. In this experiment, fast moving alpha (α)-particles were made to fall on a thin gold foil. He selected a gold foil because he wanted as thin a layer as possible.