Transition of an Electron

Transition of an Electron

When an electron makes transition from higher energy level having energy  \({{E}_{2}}\,\left( {{n}_{2}} \right)\) to a lower energy level having energy \({{E}_{1}}\,\left( {{n}_{1}} \right)\) then a photon of frequency \(\nu \) is emitted.

1) Energy of emitted radiation:

\(\Delta E={{E}_{2}}-{{E}_{1}}=\frac{-Rch{{Z}^{2}}}{n_{2}^{2}}-\left( -\frac{Rch{{Z}^{2}}}{n_{1}^{2}} \right)=-13.6{{Z}^{2}}\left( \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right)\),

\(\Delta E=-13.6{{Z}^{2}}\left( \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right)\).

2) Frequency of emitted radiation:

\(\Delta E=h\nu \Rightarrow \nu =\frac{\Delta E}{h}=\frac{{{E}_{2}}-{{E}_{2}}}{h}=Rc{{Z}^{2}}\left( \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right)\).

3) Wave number/Wavelength:

Wave number is the number of waves in unit length, \(\overline{\nu }=\frac{1}{\lambda }=\frac{\nu }{c}\),

\(\Rightarrow \frac{1}{\lambda }=R{{z}^{2}}\left( \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right)=\frac{13.6{{Z}^{2}}}{hc}\left( \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right)\).

4) Number of spectral lines:

If an electron jumps from higher energy orbit to lower energy orbit it emits radiations with various spectral lines. If electron falls from orbit \({{n}_{2}}\) to \({{n}_{1}}\) then the number of spectral lines emitted is given by:

\({{N}_{E}}=\frac{\left( {{n}_{2}}-{{n}_{1}}+1 \right)\left( {{n}_{2}}-{{n}_{1}} \right)}{2}\),

If electron from \({{n}^{th}}\) orbit to ground state ( i.e. \({{n}_{2}}=n\) and \({{n}_{1}}=1\)) then the number of spectral lines emitted is: \({{N}_{E}}=\frac{n\left( n-1 \right)}{2}\).

5) Recoiling of an atom:

Due to the transition of electron photon is emitted and the atom is recoiled.

Recoil momentum of atom = Momentum of photon

\(\frac{h}{\lambda }=hR{{Z}^{2}}\left( \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right)\),

Also recoil energy of an atom = \(\frac{{{p}^{2}}}{2m}=\frac{{{h}^{2}}}{2m{{\lambda }^{2}}}\) ; where, \(m=\)Mass of recoil atom.