Ionic solids are comparatively brittle and are poor

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: can be reheated and re-formed over and over again. As a result, TPs are generally much easier to recycle than their TS counterparts. SUMMARY .......................................................................................................................................................................... | v v The atomic scale structure of a material— the atoms present, the types of bonds between the atoms, and the way the atoms are packed together — controls many of the important macroscopic engineering properties of that material. To understand the relationship between atomic scale structures and physical properties, one must apply concepts from other disciplines such as quantum mechanics, thermodynamics, and kinetics. The two major classes of bonds are primary and secondary bonds. Primary bonds are one to two orders of magnitude stronger than secondary bonds. The three types of primary bonds are ionic, covalent, and metallic bonds. The formation of an ionic bond involves electron transfer from the electropositive element to the electronegative element. This charge transfer results in a coulombic force | e-Text Main Menu | Textbook Table of Contents pg055 [R] G1 7-27060 / IRWIN / Schaffer ak Chapter 2 01-03-98 pgm 1-19-98 QC2 Atomic Scale Structures 55 of attraction between the ions. Ionic solids are comparatively brittle and are poor conductors of electricity. Covalent bonds are favored when all the atoms are electronegative. Each atom obtains a filled valence shell by sharing electrons with its nearest-neighbor atoms. These shared electrons are spatially localized, and therefore, covalent bonds have specific bond angles associated with them. Examples of covalently bonded solids include Si, Ge, diamond, most polymers, and most organic molecules. Metallic bonds are favored when all the atoms are electropositive and when the atoms have three or fewer valence electrons. These elements also share electrons, but the shared electrons are delocalized and form an electron cloud around the metal ion cores. The delocalized valence electrons lead t...
View Full Document

Ask a homework question - tutors are online