1. MATERIALS SCIENCE &ENGINEERING Anandh Subramaniam & Kantesh Balani Materials Science and Engineering (MSE) Indian Institute of Technology, Kanpur- 208016 Email: anandh@iitk.ac.in, URL: home.iitk.ac.in/~anandh AN INTRODUCTORY E-BOOK Part of http://home.iitk.ac.in/~anandh/E-book.htm A Learner’s Guide

2.  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/Å 3  C (diamond) → ~5.0 electron/Å 3  The figure on the next slide gives a schematic representation of progress from a covalent crystal to a ionic crystal Ionicity of the chemical bond

3. Covalent to Ionic crystals Covalent Crystal Slightly ionic To ‘ideal’ ionic Increasing ionicity Ionic Crystal