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-
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.
=> When beam of high energy α- particles was directed at gold foil then tiny flash of light observed at photographic plate.
Rutherford observed that-
1) Most of the α- practical passed through gold foil undeflected :
2) A small fraction of α- particles was deflected by small angles.
3) A very few α- 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 α- particles passed undeflected.
2) Few +ve charged α- particles were deflected.
Because + ve charge of the atom present in center in very small volume that repelled & deflected the +ve charged α- 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