Rutherford Model of Atom
This experiment is also known as alpa (
) particle scattering experiment. Rutherford bombard alpha particle on gold foil of thickness 0.0004cm and found that-
) particle scattering experiment. Rutherford bombard alpha particle on gold foil of thickness 0.0004cm and found that-
1. So many particles passes through the gold foil without any deflection.
2. Some alpha particle are deflected at different angles.
3. Very few about 1 in 20,000 are bounced back (at 360 degree) from gold foil.
 |
| Rutherford Atomic Model |
Rutherford concluded nuclear model of atom as-
1. Most of the part of the atom is hollow and neutral so alpha particles passes straight without any deflection.
2. All positive charge is present in center of atom so alpha particle
are deflected at different angles by repulsion from positively charged
center known as nucleus.
3. Only very few particles bounced back so size of nucleus is very small as compared to size of atom.
4. Electron moves around nucleus like planet moves around sun in orbits.
5. Mass of electron is negligible so all mass of atom is present in nucleus.
6. Atom is electrically neutral so number of electron is equal to number of proton present in atom.
Defects of Rutherford Atomic Model
1. Stability of atom is not explained on the basis of this model.
2. This model could not explain discrete spectrum.
Rutherford’s nuclear model of atom
=> Given
by Rutherford & his students Ernest Marsden and Hans Geiger.
=> By
ฮฑ- particles scattering experiment-
 |
Rutherford’s nuclear model of atom |
=> When
beam of high energy ฮฑ- particles was directed at gold foil then tiny flash of
light observed at photographic plate.
Rutherford observed that-
1) Most
of the ฮฑ- practical passed
through gold foil undeflected :
2) A
small fraction of ฮฑ- particles was deflected by small angles.
3) A
very few ฮฑ- particles (about 1 in 20000) bounced back means deflected by nearly
1800
From above observations he concludes the structure of atom.
1) Most
of space in atom is empty because most of ฮฑ- particles passed undeflected.
2) Few
+ve charged ฮฑ- particles were deflected.
Because
+ ve charge of the atom present in center in very small volume that repelled
& deflected the +ve charged ฮฑ- particles.
3) Volume
of nucleus is negligible as compared to total volume of atom
i.e. radius of atom = 10-10m (approx)
radius
of nucleus = 10-15m (approx)
On the basis of observation & conclusion Rutherford proposed model of atom as-
1) +ve
charge & most of mass present in the center of atom known as nucleus.
2) Electrons
moves around nucleus with very high speed in circular paths known as orbits.
3) Electrons
and nucleus (protons) are held together by electrostatic force of attraction
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