Question

[6] (a) Explain the structure and spectra of hydrogenic atoms?

(b) Explain the molecular orbital theory with polar molecule hydrochloride?

[7] Summarize the different vibration modes of polyatomic molecules in Infrared spectroscopy?

[8] Explain the Integrated rate law with an example?

Answer 1

6. (a) Hydrogenic atoms contain only one electron, which revolves in the first orbit. Depending on the amount of energy absorbed, the electron will promote to any one of the higher energy states. Now, the excited electron may directly come down to the ground state or it comes to ground state through various intermediate states. As a result, the following series arise in their atomic spectra.

i) Lyman series: n₁ = 1 and n₂ = 2, 3, 4, .........

(ii) Balmer series: n₁ = 2 and n₂ = 3, 4, 5, .........

(iii) Paschen series: n₁ = 3 and n₂ = 4, 5, 6, .........

(iv) Brackett series: n₁ = 4 and n₂ = 5, 6, 7, .........

(v) Pfund series: n₁ = 5 and n₂ = 6, 7, 8, .........

(b) Molecular orbital diagram of hydrogen chloride (HCl):

Where AO = atomic orbital and MO = molecular orbital and nb = non-bonding.

Hydrogen lies at high energy due to its low electronegativity, whereas the chlorine at low energy due to its high electronegativity.