Question

5) Give the essential postulates of Bohr's model of an atom. How did it explain
1) the stability of an atom.
2)Origin of spectral lines in hydrogen atom.
5)​

Answer 1

Answer:

According to Bohr's theory , electrons revolve in definite circular orbits around the nucleus and these orbits are designated by the letters K, L, M, N or by the numbers 1, 2 ,3, 4 and so on.

2. As long as the electrons revolve in a particular orbit they can neither gain energy nor loose energy. Such orbits are called as stationary orbits or stationary states.

3. When an electron jumps from an higher orbit to a lower orbit it releases energy in the form of raldiations and when an electron jumps from lower orbit to a higher orbit it absorbs energy in the form of raldiations.

4. The angular momentum of aln electron is an integral multiple of

2π

h

mvr=

2π

nh

5. It explains the stability of an atom and also the line spectrum of hydrogen atom

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Answer 2

Final answer:

(i) According to Bohr’s model energy of an electron in an atom is not lost, the electron in an atom neither emits nor absorbs energy, hence the atom is stable.

(ii) A group of spectral lines arising from a hydrogen atom due to electrons moving from the higher energy states to a particular lower energy state.

Given that: We are given Bohr's model of an atom.

To find: We have to find the essential postulates and how this model explains the given properties.

Explanation:

Postulates of Bohr’s model of an atom:

• Electrones can revolve around the nucleus in a circular path having a fixed radius and energy, these paths are called orbits, stationary states or allowed energy states. These orbits (paths) are arranged concentrically around the nucleus and they are designated by letters K, L, M, and N or by numbers 1, 2, 3, 4 and so on.

• Radiation can occur only when an electron in one orbit jumps to another.

• Atom will be completely stable when it is in the smallest orbit since there is no orbit of lower energy into which the electron can jump.

• The angular momentum ($mvr$) of an electron is, $mvr = \frac{nh}{2\pi }$

Where '$n$' is an integer.

• This model explains the line spectrum of the hydrogen atom and the stability of an atom.

(i) The stability of an atom:

• Electron in an atom neither emits nor absorbs energy.

• The only way of electron gain energy is when it jumps to a higher energy level from a lower energy level.

• They lose energy when they jump down to a lower energy level from a higher one.

• It does not radiate energy when it is at a lower energy level.

Hence, the atom will be stable.

(ii) Bohr tells us that, radiation (energy) of a particular wavelength or frequency is absorbed if the electron moves from the smaller orbit to the higher orbit, whereas the radiation (energy) of a particular wavelength or frequency is emitted if the electron moves from a higher orbit to the lower orbit. This explains the origin of spectral lines in the hydrogen (H) atoms.

Five series of a Hydrogen spectrum are:

• Lyman series: Electron jumps from any higher orbit to the first orbit.

• Balmer series: Electron jumps from any higher orbit to the second orbit.

• Paschen series: Electron jumps from any higher orbit to the third orbit.

• Bracket series: Electron jumps from any higher orbit to the fourth orbit.

• Pfund series: Electron jumps from any higher orbit to the fifth orbit.

Hence, Bohr’s model explains the origin of spectral lines in the hydrogen atom.

To know more about the concept please go through the links

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