- Orbits
- Shells
- Energy levels
- Radiation
- Energy
- Electron
- Quantum mechanics
- Fixed size and energy
- Distribution of electrons

Bohr put forward the following postulates for the structure of atom

A) Only certain special orbits known as discrete orbits for electrons are allowed inside an atom

B) While revolving in discrete orbits the electrons do not radiate energy

- In order to overcome the objections raised against Rutherford’s model of atom, Bohr proposed his atomic model
- The orbits or shells are called as energy levels
- These orbits are represented by the letters K, L, M, N…. or by the numbers n = 1, 2, 3, 4…..
- The distribution of electrons in various orbits is proposed by Bohr and Bury. According to their theory
- The maximum number of electrons present in an orbit is given by 2n
^{2}, where ‘n’ denotes the number of the shell. First orbit or K – shell will have a maximum of 2 × 1^{2}= 2 electrons - Second orbit or L – shell can hold a maximum of 2 × 2
^{2}= 18 electrons - Third orbit or M – shell can hold a maximum of 2 × 3
^{2}= 18 electrons - Fourth orbit or N – shell can hold a maximum of 2 × 4
^{2}= 32 electrons and so on - The motion of the electrons in the Rutherford model was unstable because, according to classical mechanics and electromagnetic theory, any charged particle moving on a curved path emits electromagnetic radiation: thus, the electrons would lose energy and spiral into the nucleus
- To remedy the stability problem, Bohr modified the Rutherford model by requiring that the electrons move in orbits of fixed size and energy. The energy of an electron depends on the size of the orbit and is lower for smaller orbits
- Radiation can occur only when the electron jumps from one orbit to another
- The atom will be completely stable in the state with the smallest orbit, since there is no orbit of lower energy into which the electron can jump
- The modern model of the atom is based on quantum mechanics
- The Bohr Model contains some errors, but it is important because it describes most of the accepted features of atomic theory without the entire high-level math of the modern version

- Electrons orbit the nucleus in orbits that have a set size and energy
- The energy of the orbit is related to its size. The lowest energy is found in the smallest orbit
- Radiation is absorbed or emitted when an electron moves from one orbit to another
- The simplest example of the Bohr Model is for the hydrogen atom (Z = 1) or for a hydrogen-like ion (Z > 1), in which a negatively-charged electron orbits a small positively charged nucleus