Atomic models
Thomson’s model of an atom Thomson proposed the model of an atom to be similar to that of the Christmas pudding. Thomson proposed that An atom consists of a positively […]
Chemistry for life
Thomson’s model of an atom Thomson proposed the model of an atom to be similar to that of the Christmas pudding. Thomson proposed that An atom consists of a positively […]
Thomson’s model of an atom
Thomson proposed the model of an atom to be similar to that of the Christmas pudding. Thomson proposed that
Drawbacks
Although Thomson’s model explained that atoms are electrically neutral but the result of the experiment carried out by other scientists like alpha particle scattering experiment could not be explained by Thomson’s model of atom and it also could not explain that there was empty space in atom so it failed.
Rutherford’s model of an atom
Rutherford and his students in 1911 performed alpha particle scattering experiment in which they bombarded very thin gold foil with alpha particles.
Observations:-
Conclusions :-
From above observations following conclusions were made:-
On the basis of observations and conclusions, Rutherford proposed the nuclear model of atom according to this model,
Drawbacks
According to the classical theory of electro dynamics, any charge or particle in a circular orbit would undergo acceleration and during centripetal acceleration the charged particle would lose the energy in the form of radiations and thus it will lose energy also and it will start moving in a spiral path which will keep on decreasing its radius and that electron will ultimately fall into the nucleus and the atom will collapse this shows that Atom is highly unstable, but we all know that atoms are quite stable and due to this reason the model was discarded.
Bohr’s Model of an atom
Neils Bohr in 1913 used the concept of quantisation to clear the objections on Rutherford‘s model of atom .
Here are the postulates of Bohr’s atomic model:-
1. The electrons continue revolving in their respective orbits without losing energy does each orbit is associated with the definite energy hence, it is also called energy level.
These orbits are represented by the letters K,L, M, N, . Or the numbers, n= 1,2,3,4,….
2. The electrons keep revolving in the same orbit as the centrifugal force of a revolving electron is counter balanced by the electrostatic force between the electron and the nucleus.
3. The electrons are allowed to move in only those orbitals whose angular momentum (mvr) is a whole number multiple of h/2π. That is it is quantised.
mvr = nh/2 π ; n= 1,2,3,4,…..
4.The electron absorbs energy for jumping from lower energy orbital(shell) to Higher energy shell, and it loses the energy while coming from high energy orbital to the low energy orbital. ∆E = E2 – E1 = hc/λ
Drawbacks
1. This model was unable to explain the bond formed by atoms to form molecules.
2. It could not explain the splitting of spectral lines in magnetic and electric field.
3.This model was able to explain the spectral lines of hydrogen atom only.