Plum Pudding Model(Thomson's atomic model)
Thomson's atomic model states that an atom has a positive sphere charge with electrons embedded inside it. He compared the atom with a plum pudding,as the electrons according to him seemed like the dry fruits embedded in the spherical pudding.
Rutherford's Model
However Rutherford bombarded high energy streams of α-particles on a thin gold foil of 100 nm thickness. The deflection produced by the trajectory of these high energy α-particles after interaction with the thin sheet of gold was studied by placing a screen made up of zinc sulfide around the gold foil. The major observations made by Rutherford were that a very huge fraction of α-particles passed through the gold sheet without getting deflected. Thus he concluded that the major part of an atom must be empty.
Very few α-particles got deflected minutely or at very small angles by the gold sheet when they were bombarded against it. Also very few particles got deflected at large angles. This made him conclude that the positive charge is concentrated in a very small region and is not distributed uniformly.
From the above observations he gave the following postulates:
An atom is made up of positively charged particles. The mass of an atom was concentrated in small region which is named as the nucleus of an atom. The nucleus is surrounded by electrons which are negatively charged particles which revolve around the nucleus in a fixed circular path called as “orbits.”
An atom is electrically neutral because electrons are negatively charged and the nucleus is positively charged. The electrons are held by the nucleus due to a strong electrostatic force.Compared to the total size of an atom the size of the nucleus is very small.
