Transcript Slide 1

Part of
MATERIALS SCIENCE
& A Learner’s Guide
ENGINEERING
AN INTRODUCTORY E-BOOK
Anandh Subramaniam & Kantesh Balani
Materials Science and Engineering (MSE)
Indian Institute of Technology, Kanpur- 208016
Email: [email protected], URL: home.iitk.ac.in/~anandh
http://home.iitk.ac.in/~anandh/E-book.htm
Ionicity of the chemical bond
 Metallic, covalent and ionic bonds are extreme cases and often the nature of the
bonding is between these perfect scenarios
 In the Covalent bond picture the electrons are equally shared by the participating
atomic species  high electron density between nuclei
 In the Ionic bond picture the electron is completely transferred to one of the
participating species  high electron density around one of the nuclei
 In the metallic bond picture the electron belongs to the solid as a whole 
uniform electron density in the whole crystal
 If one looks at the electron density midway between the nuclei:
 NaCl → ~0.1 electron/Å3
 C (diamond) → ~5.0 electron/Å3
 The figure on the next slide gives a schematic representation of progress from a
covalent crystal to a ionic crystal
Covalent to Ionic crystals
Slightly ionic
Covalent Crystal
Increasing ionicity
To ‘ideal’ ionic
Ionic Crystal