The energy is emitted when an electron jumps from a higher energy level and energy is absorbed when an electron jumps from a lower energy level to higher energy levels. only those orbits are permitted in which the angular momentum (mvr) of the electron is the whole number multiple of h/2π (‘h’ is a Planck’s constant i.e. electron in the particular orbits does not lose or gain energy. The electron in an atom revolve around the nucleus only in certain selected circular paths called orbits each orbit have a definite amount of energy.

The energy of quanta is quantised, thus, E= hv.

Where h is the Planck’s Constant (6.626 × 10 -34 Js)

The energy of quanta (E) is proportional to its frequency ( v).

The energy emitted or absorbed by the atoms and molecules will be in the form of discrete packets of energy called quanta.

The main postulates of this theory are as follows:

Neils Bohr’s Atomic model( 1913 ): Neils Bohrs proposed this atomic model which is based upon Planck’s quantum theory of radiation.

The ∝-particle scattering experiments performed by rutherfords are concerned with the discovery of the nucleus.

Rutherford’s Atomic model ( 1912 ): This model was based upon ∝-particle scattering experiment.

This model is also called the plum pudding model and watermelon model. according to Thomson, an atom is a positively charged uniform sphere of radius 10 -8 cm in which electrons are embedded in such a way that the negative charge is equal to the positive charge.

Thomson’s Atomic Model: The first simple model of the atom was proposed by J.J Thomson.Various atomic models were proposed to show the arrangements and distribution of particles within an atom The electron in an atom moves from a lower energy level to a higher energy level by gaining the required energy and the electron moves from a higher energy level to a lower energy level by losing energy.shells and when the electron attains the lowest energy level, it is said to be in the ground state. The orbits n=1, 2, 3, 4… assigned as K, L, M, N…. This range of quantum numbers starts from the nucleus side with n=1 having the lowest energy level. The energy levels are represented by an integer (n = 1, 2, 3…) known as a quantum number.Each orbit or shell has fixed energy & these circular orbits are known as orbital shells.In an atom, electrons (negatively charged) revolve around a positively charged nucleus in a definite circular path called orbits or shells.The change in energy of an electron occurs when it jumps from a lower energy level to a higher energy level or vice versa. Neil Bohr proposed the stability of the atoms through the concept of the revolution of electrons in different energy levels.

Bohr found that electron located away from nucleus has more energy, and electrons close to the nucleus have less energy. Bohr model consists of a small nucleus (positively charged) surrounded by negative electrons moving around the nucleus in orbits. Rutherford basically explained the nucleus of an atom and Bohr modified that model into electrons and energy level. Bohr modified his atomic structure model by explaining that electrons move in fixed orbitals (shells) and not anywhere in between and he also explained that each orbit (shell) has fixed energy levels. Rutherford’s model introduces the nuclear model of the atom, in which he explained that a nucleus (positively charged) is surrounded by negatively charged electrons. It came into existence with the modification of Rutherford’s model of the atom. ISRO CS Syllabus for Scientist/Engineer Examīohr model of the atom was explained by Neil Bohr in 1915.ISRO CS Original Papers and Official Keys.GATE CS Original Papers and Official Keys.

Niels bohr atomic theory