Solid State Chemistry (CMS4105)

BSc, Chemistry - CHMS

Semester: First Semester

Level: 400

Year: 2019

Answers (200 )
The UNIVERSITY OF BAMENDA
P.O. Box 39 Bambili
Department: CHEMISTRY
Lecturer(s): Dr. MBOM D. Y.
Course
-
title:
SOLID STATE CHEMISTRY
Page 1 of 2
REPUBLIC OF CAMEROON
Pe a c e
-
W or k -F a t h er la n d
School/Faculty: SCIENCE
Course Code: CHM54105
Date: 14/03/2019
Instructions: Answer all
questions.
Question 1 (25 marks)
a) Differe ntiate clearly between the terms lattice, space lattice, unit cell, and crystal
structure. What lattice constants define a unit cell? (6 marks)
b) Sket ch the BCC Bravais lattice and determine the packing fraction. (4 marks)
c) Draw the following crystallogra phic planes in an FCC unit cell (i) ( 110) (ii) (121) a nd
(iii) (321) (3 marks)
d) (i) What are X-rays and how are they produced?
( i i ) W h y d o c r y s t a l s d i f f r a c t X - r a y s ?
( i i i ) The glancing angle of a Bragg reflection from a set of crystal planes separated
by 99.3 pm is 20.85
o
. Calculate the wavelength of the X-rays.
( i v ) What are the values for 2θ of the first three diffraction lines of bcc iron (atomic
radius 126 pm) when X-rays of wavelength 58 pm are used? (6 marks)
e) The d
3 1 0
interplanar spacing in a BCC element is 0.1587 nm. (3 marks)
i) What is its lattice constant a?
ii)
Wha t is t he atomic r adiu s of th e elemen t?
f)
A hyp othetical AX type of ceramic material is known to ha ve a density of 2.65 g/cm
3
and a unit ce ll of cubic symm etry with a cell edge length of 0.43 nm. The atomic
weights of the A a nd X elements are 86.6 and 40.3 g/mol, resp ectively. On the basis
of this information, which of We following crystal structures is (are) possible for this
material: rock salt, cesium chloride, or zinc blende? Justify your choice(s). (3 marks)
Asanji Hall
-
15.00
Duration: 2 H
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Page 2 of 2
Question 2 (25 marks)
a) Determine t he P.D. for a metallic system (hard sphere behavior) which crystallizes in
a simple cubic (SC) structure.
b) What is the family of planes {hkl} with an interplanar spacing of d = 1.246
Å
in Ni with
a = 3.524
Å
?
c) Covalent bonding occurs in both molecular and covalent network solids but these two
types of solids differ greatly in their hardness and m.pt. Why.
d) Show how the magnetic susceptibility varies w ith t emperatur e for paramagne tic,
antiferromagnetic and fe rromagnetic materials. (4 marks)
e) Sk e t c h t he r e s i s t a n ce v e r s u s t e m p e ra t u r e p l ot f o r ( i ) m e t a l l i c c o n du c t o r s ( i i )
semiconductor (in) superconductor (3 marks)
f) (i) Give the genera l Born-Lande eq uation for the calculation of la ttice energy. (2
marks)
(iii) C a l c u l a t e t h e l a t t i c e e n e r g y o f C a F
2
i n k J / m o l . Th e M a d e l u n g c o n s t a n t i s
2. 5 1 9 . The Bor n e x p o n e n t i s 8 . T he rad i us of C a
2
is 114 p m , the ra d i u s o f F’
117 pm and 4
= 1.112 x 10
10
C
2
/(J•m). (4 marks)
g) Explain why Lattice energy calculations based on the Born Mayer equation reproduce
the experimentally determ ined values to within 1 per cent for LiCI but only 10 per
cent for AgCl given that both compounds have the rock-salt structure.
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