Chapter Materials Science

Chapter Crystal Structures

QUESTIDN 'l a} Distinguish three {3] differences between ionic and covalent bonding with an example of it. [3 marks} b} Describe three {3} characteristics of ceramic materials. [3 marks} c} Determine the radius of Bromine {Br} when calcium {Ga2+} and Bromine {Br'} ions just touch each other in a vacuum. with the force of attraction is 4.1 x \"3'9 N. Assume that the radius of Ca2+ ion is 1.l.'.| x 1D\" m. Given the : Electron charge. e = 1.6 I 1t'.t'11g C Permittivity of free space. En = 3.35 it til-23 CZ I'll'1m4a [5 marks} QUESTION 2 a} Most metals and alloys. ceramics. and some polymers are classified as crystalline materials. i} Describe the arrangement of atoms in a crystalline material. [2 marks} ii} lIBive two {2} types of crystal stnictures that exist in most pure metals. [2 marks} iii} Gold [Au] has a FCC sthcture and its atoms are arranged more closely together than those in chromium {Gr} which has a BBC structure. Give two [2} differences between these two metals due to their crystal structures. [2 marks} b} The atomic radius of gold {Au} is [L146 nm and its atomic mass is 19? gmol". Assuming the atoms to be hard spheres that touch each other along the face diagonals of the unit cell, calculate the density of its unit cell. Given Avogadro's number1 H... = E.23 X it]?3 atoms mol-'. [5 marks}