Defects of Rutherford Model
Rutherford model of an atom resembles our solar system. It has following defects:
1. According to classical electromagnetic theory, electron being charged body will emit energy
continuously. Thus the orbit of the revolving electron becomes smaller and smaller until it would fall
into the nucleus and atomic structure would collapse.
2. If revolving electron emits energy continuously then there should be a continuous spectrum but a line
spectrum is obtained.
Bohr’s Atomic Model
Neil Bohr (1913) presented a model of atom which has removed the defects of Rutherford Model. This
model was developed for hydrogen atom which has only proton in the nucleus and one electron is
revolving around it.
Postulates of Bohr’s Atomic Model
The main postulates of Bohr’s Model are given below:
1. Electrons revolve around the nucleus in a fixed orbit.
2. As long as electron revolves in a fixed orbit it does not emit and absorb energy. Hence energy of
electron remains constant.
3. The orbit nearest to the nucleus is the first orbit and has lowest energy. When an electron absorbs
energy it jumps from lower energy orbit to higher energy orbit. Energy is emitted in the form of
radiations, when an electron jumps from higher energy orbit to lower energy orbit. The unit of energy
emitted in the form of radiations is called quantum. It explains the formation of atomic spectrum.
4. The change in energy is related with the quantum of radiation by the equation :
E2 – E1 = hv
E1 = Energy of first orbit
E2 = Energy of the second orbit
h = Planck’s constant
v = Frequency of radiation
The number of protons present in the nucleus of an atom is called atomic number or proton number. It
is denoted by z. The proton in the nucleus of an atom is equal to nu