Question

Write a note on Bohr's Model....

Answer 1

$\Large{\underline{\underline{\red{\tt{\purple{\leadsto } Bohr's\:Model\:of\:an\: Atom:-}}}}}$

➳ Electrons revolve around the nucleus in specified circular parts called orbits aur shells.

➳ Each orbit or shell is associated with a definite amount of energy hence these are also called energy levels.

➳ The energy associated with a certain energy level increases with the increase of its distance from the nucleus.

➳ As long as the electron revolves in a particular orbit the electron is not lose its energy.

➳ An electron jumps from a lower energy level to a higher energy level by absorbing energy but when it jumps from higher to lower energy level it emits energy.

➳ The electronic and revolve only in the orbit in which the angular momentum of the electron is quantized that is whole multiple of $\sf\dfrac{nh}{2\pi}$ . this is known as principal of quantization of angular momentum.

$\underline{\boxed{\red{\tt\:\dag \:\:mvr\:\:=\:\:\dfrac{nh}{2\pi}}}}$

$\tt Where$

• n is a integer .
• m is mass of electron.
• v is Velocity of electron in orbit.
• r is the distance from nucleus.

By applying the concept of quantization of energy , Bohr calculated the radiation energy of an orbit of hydrogen atom.

$\underline{\purple{\boxed{\red{\tt\:\dag \:\:Radius_n\:\:=\:\:\dfrac{n^2h^2}{4\pi me^2}}}}}$

$\underline{\orange{\boxed{\green{\tt\:\dag \:\:Energy_n\:\:=\:\:\dfrac{-2\pi^2me^4}{n^2h^2}}}}}$

$\tt Here$

• h is Planck's constant = $\sf 6.625\times10^{-34}J.s$

_____________________________________

$\underline{\purple{\bf{\leadsto Limitations \:of\:Bohr's\: Atomic\:Model:-}}}$

❒ Bohr could not explain the spectral series for multi - electron atoms.

❒ Bohr's model could not give satisfactory justification for the assumption that electrons can reduce the world in those objects where angular momentum is whole number multiple of $\sf\dfrac{nh}{2\pi}$.

❒ According to Heisenberg's in unertenaity principle , it is impossible to determine simultaneously with certainity the exact position and momentum of the particle .Bohr assume that and electron of an atom is located at a definite distance from the nucleus and revolves around the nucleus with a different Velocity .

❒ The atomic spectral lines split into a number of closely packed lines in the presence of magnetic field and electric field. These effects are known as Stark effect and Zeeman effect respectively . He failed to explain these.

❒ When the hydrogen spectrum was observed with the spectroscope of high resolving power , it was found that the individual lines in the spectrum consisted of several fine lines lying close to each other. this is called fine spectrum and field to explain the fine structure of spectrum.

Answer 2

Answer:

$\large\orange{\boxed{\boxed{Hey! }}}$

Bohr Atomic Model:-

• A Danish physicist named Neil Bohr in 1913 proposed the Bohr atomic model. He modified the problems and limitations associated with Rutherford’s model of an atom. Earlier in Rutherford Model, Rutherford explained in an atom a nucleus is positively charged and is surrounded by electrons (negatively charged particles).

According to Bohr Atomic model:

• A small positively charged nucleus is surrounded by revolving negatively charged electrons in fixed orbits. He concluded that electron will have more energy if it is located away from the nucleus whereas the electrons will have less energy if it located near the nucleus.

Postulates of the Bohr Atomic Model:

• Electrons revolve around the nucleus in a fixed circular path termed “orbits” or “shells” or “energy level.”
• The orbits are termed as “stationary orbit.”
• Every circular orbit will have a certain amount of fixed energy and these circular orbits were termed orbital shells. The electrons will not radiate energy as long as they continue to revolve around the nucleus in the fixed orbital shells.
• The different energy levels are denoted by integers such as n=1 or n=2 or n=3 and so on. These are called as quantum numbers. The range of quantum number may vary and begin from the lowest energy level (nucleus side n=1) to highest energy level.
• The different energy levels or orbits are represented in two ways such as 1, 2, 3, 4… or K, L, M, N….. shells. The lowest energy level of the electron is called the ground state.
• The change in energy occurs when the electrons jump from one energy level to other. In an atom, the electrons move from lower to higher energy level by acquiring the required energy. However, when an electron loses energy it moves from higher to lower energy level.

Therefore,

• 1st orbit (energy level) is represented as K shell and it can hold up to 2 electrons.
• 2nd orbit (energy level) is represented as L shell and it can hold up to 8 electrons.
• 3rd orbit (energy level) is represented as M shell and it can contain up to 18 electrons.
• 4th orbit (energy level) is represented as N Shell and it can contain maximum 32 electrons.And, The orbits continue to increase in a similar manner

For the fig kindly see the attachment.....