Question

what are the strengths and weaknesses of the Bohr model of the atom?

Answer 1

Strengths:

1. Bohr’s model satisfactorily explains the spectra of species having one electron, viz. hydrogen atom,He⁺, Li²⁺ etc.

2. it helps in the calculation of energy of electrons in particular orbits

E = –2π²mZ²e⁴k²/n²h²  Where, n=1, 2, 3……….∞

3. it helps in the calculation of velocity of electrons in orbits

V_n = 2πe²ZK/nh, V_n = [Ze²/mr]^1/2; V_n = 2.188 × 10⁸ Z/n cm.sec^–1

4. it helps in the calculation of radius of orbits

Calculation of radius of Bohr’s orbit : According to Bohr, radius of n^th orbit in which electron moves is

rn = [h²/4π²me²k] . n²/Z

Where, n = Orbit number, m = Mass of electron [9.1 × 10^–31 kg], e = Charge on the electron [1.6 × 10^–19] Z = Atomic number of element, k = Coulombic constant [9 × 10⁹ Nm² c^–2]

After putting the values of m,e,k,h, we get.

              r_n = n²/Z × 529 A

Weaknessess:

(i) Bohr theory was very successful in predicting and accounting the energies of line spectra of hydrogen i.e. one electron system. It could not explain the line spectra of atoms containing more than one electron.

(ii) This theory could not explain the presence of multiple spectral lines.

(iii) This theory could not explain the splitting of spectral lines in magnetic field (Zeeman effect) and in electric field (Stark effect). The intensity of these spectral lines was also not explained by the Bohr atomic model.

(iv) This theory was unable to explain of dual nature of matter as explained on the basis of De broglies concept.

(v) This theory could not explain uncertainty principle.

(vi) No conclusion was given for the concept of quantisation of energy.