what are the postulates of bohr model of atom ? why was this model proposed by bohr?

Bohr’s model includes a small positively charged nucleus in center which is  surrounded by negatively charge electrons moving around the nucleus in orbits. Bohr model showed that the energy of an electron was inversely dependent on the distance between the center(nucleus) and the electron.

Postulates of Bohr's Model of an Atom:

• In an atom negative electrons revolve around positive charge nucleus in a fix circular path which are called as orbits.
• Each orbit has a fixed energy and these circular orbits are known as orbital shells.
• The energy level of these orbits are represented using quantum numbers which are integers(n=1,2,3,4...). This range of quantum number starts from nucleus with n=1 having the lowest energy level. The orbits n=1, 2, 3, 4… are assigned as K, L, M, N…. shells and when an electron attains the lowest energy level it is said to be in the ground state.
• The electrons in an atom move from a lower energy level to a higher energy level by gaining the required energy and an electron moves from a higher energy level to lower energy level by losing energy.

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Bohr's model was proposed as a modification of the Rutherford's model. Rutherford introduced the nuclear model (i.e. nucleus is surrounded by negatively charged electrons), which was modified by Bohr by explaining electrons and their energy levels.

Postulates of Bohr's model:

• In an atom, electrons (negatively charged) revolve around the positively charged nucleus in a definite circular path called as orbits or shells.
• Each orbit or shell has a fixed energy and these circular orbits are known as orbital shells.
• The energy levels are represented by an integer (n=1, 2, 3…) known as the quantum number (https://byjus.com/chemistry/quantum-numbers-and-shapes-of-orbital/) . This range of quantum number starts from nucleus side with n=1 having the lowest energy level. The orbits n=1, 2, 3, 4… are assigned as K, L, M, N…. shells and when an electron attains the lowest energy level it is said to be in the ground state.
• The electrons in an atom move from a lower energy level to a higher energy level by gaining the required energy and an electron moves from a higher energy level to lower energy level by losing energy.

Bohr’s model includes a small positively charged nucleus in center which is  surrounded by negatively charge electrons moving around the nucleus in orbits. Bohr model showed that the energy of an electron was inversely dependent on the distance between the center(nucleus) and the electron.

Postulates of Bohr's Model of an Atom:

• In an atom negative electrons revolve around positive charge nucleus in a fix circular path which are called as orbits.
• Each orbit has a fixed energy and these circular orbits are known as orbital shells.
• The energy level of these orbits are represented using quantum numbers which are integers(n=1,2,3,4...). This range of quantum number starts from nucleus with n=1 having the lowest energy level. The orbits n=1, 2, 3, 4… are assigned as K, L, M, N…. shells and when an electron attains the lowest energy level it is said to be in the ground state.
• The electrons in an atom move from a lower energy level to a higher energy level by gaining the required energy and an electron moves from a higher energy level to lower energy level by losing energy.

Hope this helps you,

Thank You.