Test Papers / Previous Question Papers of Indira Gandhi National Open University CHE1 Atoms and Molecules June 2007

Bachelor of Science (BSc)
Term-End Examination
CHEMISTRY

CHE1: Atoms and Molecules

Time: 1 hours
Maximum Marks: 25

Note : Attempt all five questions.

Use the following data whereever required:
Velocity of light (c)= 2.998 x 10⁸ms^-1
Planck's constant (h)= 6.626 x 10 ^-34Js
Mass of electron m_e=9.109 x 10^-31kg

1. Answer any two of the following: (2)
(a) What are matter waves ?
(b) Give the SI unit for the dipole moment.
(c) What is the half-life period of a radioactive substance ?

2. Answer any two of the following: (4)
(a) Neils Bohr proposed a model for the atomic structure in 1913. State fwo reasons for the , model to be accepted at that time.

(b) A sodium vapour lamp emits a radiation of wavelength λ=589 nm. Calculate the energy of the emitted photon.

(c) An electron has a speed of 300 ms^-1 measurable accurately upto 0.01%.With what maximum accuracy can its position be determined ?

3.Answer any two of the following : (6)
(a) What is resonance ? Write the resonating structures of NO^-₃ ion.
(b) The lowest wave number absorption line in the rotational spectrum of ¹H ⁸⁰Br is at 17.17cm^-1.
( I = 3.260 x10^-47 kg m², and µ:1.640 x 10^-27 kg ).

Ansver the following questions :
(i) Which are the two energy levels involved in this transition ?
(ii) What is the value of the rotational constant (B) for HBr ?
(iii) Calculate the bond length of HBr.

(c) Consider the species O₂ and O⁺₂. Use M.O. theory to predict
(i) which of the two has a stronger bond;
(ii) which of the two has a higher magnetic moment.

4.Answer any two of the following : (8)
(a) Define hybridisation of orbitals. Explain the shape of the SF₆ molecule on the basis of hybridisation. (at. no. of S = 16).
(b) (i) The electron affinity of carbon is -122 kJ mol^-1, while that of nitrogen is +9 kJ mol^-1. Explain this.
(ii) using VSEPR theory, predict the shapes of NO^-₂ and BrF^-₄.

(c) Answer the following (i) Predict which is polar, CO₂ or SO₂, and why.
(ii) Give the selection rule for a rotational spectrum. Will H₂ give a rotational spectrum ? Justify your answer.

5.Answer any one pdd, (a) or (b): (5)
(a) (i) state Beer - tambert's law and give the mathematical relationship between absorbance and concentration.
(ii) ²³⁸₉₂U decays by emitting one α-particle followed by the emission of a β-particle. What is the number of neutrons in the new nuclide formed ?
(b) (i) What is 'electron capture' in the context of radioactive decay ?
(ii)The reduced mass of CO is 1.139 x 10^-26 kg. If the force constant of the bond between C and O is 1857 Nm^-1 calculate the wave number at which the signal would be obtained in the IR spectrum of CO.