Test Papers / Previous Question Papers of Indira Gandhi National Open University CHE1 Atoms and Molecules June 2006

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: Velocity of light (c)= 2.998 x 10⁸m

1. Answer any two parts.
(a) What is the mathematical form of the Einstein's theory of photoelectric effect?

(b) What is the Zeeman effect?

(c) How many normal modes of vibration are there in CH₃OH?

2. Answer any two parts.

(a) Predict the shapes of any two of the following molecules:

(i) XeF₄
(ii) PF^-₆
(iii) ClF₃
(iv) HgCl₂

(b) Identify the type of hybridisation for each carbon atom in the following molecules:
(i) CH₃ - COCl
(ii) HC= CH

(c) In O₂ and F₂, σ_2px molecular orbital is of lower energy than π_2py and π_2pz molecular orbitals. Explain why.

3. Attempt any two parts:

(a) What are the three components of molar polarisation of a substance? Write an expression for any one of them, giving the meaning of each symbol.

(b) For each of the following molecules, state whether it absorbs in the microwave region or not. Justify your answers.
(i) CO
(ii) Cl₂
(iii) CO₂

(c) Calculate the force constant of a diatomic molecule (AB) which absorbs at 2.143 x 10⁵m^-1 and whose reduced mass is 1.139x10^-26kg.

4. Attempt any two parts. (8)

(a) Derive the following expression for the radius r_n of the n^th stationary orbit in the Bohr model: r_n=n²e_oh² / πmZe² where the symbols have their usual meanings.

(b) Draw the lots of the variation of (i) R(r), and (ii) r²R²(r) with r/a_o for 2s and 3p atomic orbitals.

(c) Give reasons for the following:
(i) Ionic radius of F^- ion is less than that of H^- ion.
(ii) PCl₅ is formed easily but not NCl₅.

5. Attempt any one part, (a) or (b)
(a) (i) What is ionic-covalent resonance? (2)
(ii) What are the three major rules for the linear combination of atomic orbitals (LCAO)? (3)

OR

(b) (i) The dipole moment and the bond length of a diatomic molecule AB are 3.5x10^-30cm and 125 pm, respectively. Calculate the magnitude of charge on the A and the B atoms. (2)
(ii) Write balanced equations for the nuclear reactions given below: (3)
- proton emission by ⁴¹₁₉K
- neutron emission by ⁸⁸₃₅Br
- alpha emission by ¹¹₅B