Neils Bohr proposed his model in 1931. Bohr’s model is applicable only for one electron system like H, He+, Li2+ etc.
Assumptions of Bohr’s model are
1. Electrons keep revolving around the nucleus in certain fixed permissible orbits where it doesn’t gain or lose energy. These orbits are known as stationary orbits.
Number of waves in an orbit = circumstances of orbit / wavelength
2. The electrons can move only in those orbits for which the angular momentum is an integral multiple of h / 2π, i.e.,
mvr = nh / 2π
where, m = mass of electron: v = velocity of electron;
r = radius of orbit
n = number of orbit in which electrons are present
3. Energy is emitted or absorbed only when an electron Jumps from higher energy level to lower energy level and vice-versa.
ΔE = E2 – E1 = hv = hc / λ
4. The most stable state of an atom is its ground state or normal state,
From Bohr’s model, energy, velocity and radius of an electron in nth Bohr orbit are
(i) Velocity of an electron in nth Bohr orbit
(vn) = 2.165 * 106 Z / n m / s
(ii) Radius of nth Bohr orbit
(rn) = 0.53 * 10-10 n2 / Z m = 0.53 n2 / Z A
where, 11 = number of shell; Z = atomic number
As we go away from the nucleus, the energy levels come closer, i.e., with the increase in the value of n, the difference of energy between successive orbits decreases.
Thus. E2 – E1 > E3 – E2 > E4 – E3 > E5 – E4etc.
0 Comments:
Post a Comment