A.Bohr'sModel of Atom:Neils Bohr (1913) developed a new theory of the atomic structure on the basis of Quantum theory of radiation. The main points of his theory are :
1. An atom consists of a dense nucleus situated at the centre, around which the electrons revolve in circular orbit.
2. Of the very large number of possible circ'ular orbits around the nucleus, the electron can move only in certain fixed orbits known as stationary states.
3. Stationary staes does not mean that the electrons are stationary. An electron keeps on revolving in the same orbit and its energy remains constant.
4. Each fixed or stationary state is associated with a definite amount of energy, these different energy levels are numbered as 1, 2, 3, 4 etc. or alternatively they are designated as K, L, M, N shell etc.
5. The electron in an atom can have certain definite or disc.rete values of energy which are characteristic of that atom. In other words the electronic energy of an atom is quantized.
6. The electron in an atom can revolve only in those ener.gy levels for which the angular momentum of an electron is an integral multiple of , i.e.
For circular motion, the magnitude of the angular momentum L of the electron is L = mvr
Bohr's quantization of an angular momentum is L = mvr = (where n = 1, 2, etc.)
Here the integer n is called principal quantum number.
where, m - mass of an electron
v - velocity
r - radius of orbit in which the electron is moving
n - orbit of the electron
Electrons orbit in certain stationary states, in which the orbiting electron do not continously radia.te electromagnetic energy. The stationary states have definite total energy. This assumption implies that classical law of electromagnetic radiation by an accelerated charge does not apply to an electron in its stationary orbits.
7. The emission or absorp.tion of electromagnetic radiation occurs only when there is a transition of electrons between two stationary states. When an electron jumps from a higher energy orbit to a lower energy orbit, the excess energy is emitted as photons. The frequency of the emitted or absorb radiation is proportional to the difference in energy of to stationary state.s, ∆E = E - E = hv , where h is the Planck's constant, h = 6.625 × 10²⁷ erg-s. E and E are the energies of the initial and final states. The frequency of the photon is independent of the frequency of the electrons orbital motion.
This assumption is equivalent to that of conservation of energy with the emission of photon.
B. Expression for the energy of an electron in the atom : Let total energy be equal to the sum of kinetic energy and the potential energy.
=> TO , overcome the drawback of Rutherford's model of atom and to exaplain the line spectrum of Hydrogen Neil's Bohr a Danish physicist in 1913 proposed a new model of atom based upon Planck's Quantum Theory .This new model is called Bohr's Model of atom.
● An atom consists of a small , heavy positively charged nucleus in the centre and the electrons revolve around it in circular orbit.
● In Bohr's Model of atom the word stationary does not mean that the Electrons are stationary but it means that the energy of the Electron revolving in a particular orbit is fixed and doesn't change with Time.
● The different energy levels are numbered as 1,2,3...etc or designed as K,L,M,N,O,P ..etc starting from the shell closest to the nucleus
● Like energy ,the angular momentum of an electron in an atom can have certain definate values or discrete values and not any value of its own. The only permissible values of angular momentum are given by the following expression :-
here m is the mass of the Electron, v is the tangential velocity of revolving electron ,r is the radius of the orbit ,h is the Planck's constant and n is the integer.
● When the electrons in an atom are in their Lowest (normal ) energy level or State ,they keep on revolving in Thier respective Orbits without losing energy beacause energy can neither be lost nor gained continuously . This state is called normal or ground state.
● Energy is emitted or absorbed Only when the electrons jump from one orbit to the . The amount of energy emitted or absorbed is given by the difference of energies of the two levels of energy levels concerned i.e
∆E= E2 - E1
Where E2 and E1 are the energies of the Electron in the higher and lower energy levels respectively and ∆E is the difference in engergies of the two levels.
● Energy is absorbed when electron jumps from a lower energy levels to some higher energy level.
● Energy is emitted when an electron jumps from a higher level to some lower energy level.
Answers & Comments
A. Bohr's Model of Atom : Neils Bohr (1913) developed a new theory of the atomic structure on the basis of Quantum theory of radiation. The main points of his theory are :
1. An atom consists of a dense nucleus situated at the centre, around which the electrons revolve in circular orbit.
2. Of the very large number of possible circ'ular orbits around the nucleus, the electron can move only in certain fixed orbits known as stationary states.
3. Stationary staes does not mean that the electrons are stationary. An electron keeps on revolving in the same orbit and its energy remains constant.
4. Each fixed or stationary state is associated with a definite amount of energy, these different energy levels are numbered as 1, 2, 3, 4 etc. or alternatively they are designated as K, L, M, N shell etc.
5. The electron in an atom can have certain definite or disc.rete values of energy which are characteristic of that atom. In other words the electronic energy of an atom is quantized.
6. The electron in an atom can revolve only in those ener.gy levels for which the angular momentum of an electron is an integral multiple of
, i.e.
For circular motion, the magnitude of the angular momentum L of the electron is L = mvr
Bohr's quantization of an angular momentum is L = mvr =
(where n = 1, 2, etc.)
Here the integer n is called principal quantum number.
where, m - mass of an electron
v - velocity
r - radius of orbit in which the electron is moving
n - orbit of the electron
Electrons orbit in certain stationary states, in which the orbiting electron do not continously radia.te electromagnetic energy. The stationary states have definite total energy. This assumption implies that classical law of electromagnetic radiation by an accelerated charge does not apply to an electron in its stationary orbits.
7. The emission or absorp.tion of electromagnetic radiation occurs only when there is a transition of electrons between two stationary states. When an electron jumps from a higher energy orbit to a lower energy orbit, the excess energy is emitted as photons. The frequency of the emitted or absorb radiation is proportional to the difference in energy of to stationary state.s, ∆E = E
- E
= hv , where h is the Planck's constant, h = 6.625 × 10²⁷ erg-s. E
and E
are the energies of the initial and final states. The frequency of the photon is independent of the frequency of the electrons orbital motion.
This assumption is equivalent to that of conservation of energy with the emission of photon.
B. Expression for the energy of an electron in the atom : Let total energy be equal to the sum of kinetic energy and the potential energy.
[ Refer to the attachment. ]
=> TO , overcome the drawback of Rutherford's model of atom and to exaplain the line spectrum of Hydrogen Neil's Bohr a Danish physicist in 1913 proposed a new model of atom based upon Planck's Quantum Theory .This new model is called Bohr's Model of atom.
● An atom consists of a small , heavy positively charged nucleus in the centre and the electrons revolve around it in circular orbit.
● In Bohr's Model of atom the word stationary does not mean that the Electrons are stationary but it means that the energy of the Electron revolving in a particular orbit is fixed and doesn't change with Time.
● The different energy levels are numbered as 1,2,3...etc or designed as K,L,M,N,O,P ..etc starting from the shell closest to the nucleus
● Like energy ,the angular momentum of an electron in an atom can have certain definate values or discrete values and not any value of its own. The only permissible values of angular momentum are given by the following expression :-
here m is the mass of the Electron, v is the tangential velocity of revolving electron ,r is the radius of the orbit ,h is the Planck's constant and n is the integer.
● When the electrons in an atom are in their Lowest (normal ) energy level or State ,they keep on revolving in Thier respective Orbits without losing energy beacause energy can neither be lost nor gained continuously . This state is called normal or ground state.
● Energy is emitted or absorbed Only when the electrons jump from one orbit to the . The amount of energy emitted or absorbed is given by the difference of energies of the two levels of energy levels concerned i.e
∆E= E2 - E1
Where E2 and E1 are the energies of the Electron in the higher and lower energy levels respectively and ∆E is the difference in engergies of the two levels.
● Energy is absorbed when electron jumps from a lower energy levels to some higher energy level.
● Energy is emitted when an electron jumps from a higher level to some lower energy level.
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