Submit questions marked by*
Due Date: 27th October, 2017
EG 244, MATERIAL SCIENCE I
Tutorial + Assignment 1
Note: For day students assignment is
group work. Maximum number per
group is 10
1. Cite the difference between atomic mass and atomic weight
2. (a) Briefly cite the main differences between ionic, covalent and metallic bonding
(b) State the Pauli Exclusion Principle.
3. Why are covalently bonded materials less dense than ionic or metallic bonded materials?
4. Compute the percentage ionic character of the interatomic bond for each of the following compound: MgO
5. What type(s) of bonding would be expected for each of the following materials: Solid xenon, bronze, rubber?
6. Explain why hydrogen fluoride (HF) has a higher boiling temperature than hydrogen chloride (HCl) (19.4 vs
85oC) even though HF has a lower molecular weight.
7. The net potential energy between two adjacent ions, 𝐸𝑁 may be represented by the equation
𝐴 𝐵
𝐸𝑁 = − + 𝑛
𝑟 𝑟
Calculate the bonding energy 𝐸𝑜 in terms of the parameters 𝐴, 𝐵, and 𝑛 using the following procedure:
a) Differentiate 𝐸𝑁 with respect to 𝑟 and then set the resulting expression to zero, since the curve of 𝐸𝑁
versus 𝑟 is a minimum at 𝐸𝑜
b) Solve for the 𝑟 in terms of 𝐴, 𝐵 and 𝑛 which yields 𝑟𝑜 , the equilibrium interatomic spacing
c) Determine the expression for 𝐸𝑜 by substituting 𝑟𝑜
8. The element titanium has atomic number 22 and atomic weight 47.9.
(a) State in one sentence each what these numbers tell you about single atoms of titanium.
(b) Determine: (i) the number of atoms in 1 mole of titanium, (ii) the mass of 1 mole of titanium, and (iii) the
mass of one atom of titanium.
9. Iron has the BCC crystal structure with two atoms per unit cell. The lattice parameter is 0.2867nm. Estimate
the atomic radius.
10. *Calculate the radius of a palladium atom, given that Pd has an FCC crystal structure, a density of 12.0
g/cm3, and an atomic weight of 106.4 g/mol.
̅ (c) [102]
̅
11. Within a cubic unit cell, sketch the following directions: (a) [101] (b) [1̅11]
12. Sketch within a cubic unit cell the following planes: (a) (101̅) (b) (1̅11̅)
13. Below is a unit cell for a hypothetical metal. (a) To which crystal system does this unit cell belong? (b) What
would this crystal structure be called? (c) Calculate the density of the material, given that its atomic weight is
141 g/mol.
14. For a brass alloy, the stress at which plastic deformation begins is 345 MPa, and the modulus of elasticity is
103 GPa. (a) What is the maximum load that may be applied to a specimen with a cross-sectional area of 130
mm2 without plastic deformation? (b) If the original specimen length is 76 mm, what is the maximum length
to which it may be stretched without causing plastic deformation?
15. Using your knowledge of interatomic bonding types, explain why (a) Metals are good electrical and thermal
conductors (b) Ceramics are often brittle (c) Polymers are generally less dense than metals.
16. *The following data were collected from a 12 𝑚𝑚 diameter test specimen of magnesium (𝑙𝑜 = 30.00 𝑚𝑚)
Load (N)
0
5.000
10.000
15.000
20.000
25.000
26.500
27.000
26.500
25.000
Gauge Length
(mm)
30.000
30.0296
30.0592
30.0888
30.15
30.51
30.90
31.50
32.10
32.79
Stress MPa
0
44.2
88.4
132.6
176.8
221.0
234.3
238.7
234.3
221.0
Strain
(mm/mm)
0.0
0.000987
0.001973
0.00296
0.005
0.017
0.030
0.050
0.070
0.093
After fracture, the gauge length is 32.61 𝑚𝑚 and the diameter is 11.74 𝑚𝑚. Plot the data and calculate
a) The 0.2% offset yield strength
b) The tensile strength
c) The modulus of elasticity
d) The % elongation
e) The % reduction in area
f) The engineering stress at fracture
g) The true stress at fracture and
h) The modulus of resilience
17. *A cylindrical specimen of a hypothetical metal alloy is stressed in compression. If its original and final
diameter are 20.000 and 20.025 𝑚𝑚, respectively, and its final length is 74.96 𝑚𝑚, compute its original
length if the deformation is totally elastic. The elastic and shear moduli for this alloy are 105 𝐺𝑃𝑎 and
39.7 𝐺𝑃𝑎 respectively.