ESO205A: Nature and Properties of Materials
2022-2023 Semester I
Assignment #1
(due date: August 10)
1. Explain why hydrogen fluoride (HF) has a higher boiling temperature than hydrogen chloride (HCl)
{19.4 vs –85°C}, even though HF has lower molecular weight.
2. Calculate the force of attraction between a K+ and O2- ion the center of which are separated by a
distance of 1.5 nm.
3. What type of bonding is expected for each of the following materials:
Brass;
rubber;
BaS; bronze;
nylon;
AlP.
4. The net bonding energy UN between two isolated positive and negative ions is a function of interionic distance r as follows:
UN = -A/r + B/rn
where A, B, and n are constants for the particular ion pair. The same equation is also valid for
bonding energy between adjacent ions in solid materials.
Derive an expression for the dependence of the modulus of elasticity, E, in terms of the parameters
A, B, and n.
5. For the given elements of the same period, the binding energies and melting point are found to be as
follows:
Element:
B.E. (kJ/mol):
m.p. (°C):
Na
27
98
Mg
25
650
Al
54
660
Si
P
176 214
1410 44
S
243
119
Cl
242
101
Explain why the melting point first increases and then decreases even though the bond energy
increased from Na to Cl.
6. Draw neatly labeled unit cells of the seven crystal systems and indicate their axial relationships.
7. There are two atoms of the same kind per unit cell located at 0 ½ 0 and ½ 0 ½ in an orthorhombic
lattice. What is the bravais lattice?