bei48482_FM

349

Table 10.1

Types of Crystalline Solids. The cohesive energy is the work needed to remove an atom (or molecule) from the crystal and so

indicates the strength of the bonds holding it in place.Type

lonic

Covalent

Molecular

Metallic

Lattice BondProperties Example

Negative ionPositive ion

Metal ionElectron gas

Shared electrons

Instantaneous chargeseparation in molecule

Electric attractionHard; high melting points; may besoluble in polar liquids such aswater; electrical insulators (butconductors in solution) Sodium chloride, NaCl Ecohesive



3.28 eV/atom

Shared electronsVery hard; high melting points;insoluble in nearly all liquids; semi-conductors (except diamond, which is an insulator)Diamond, C Ecohesive



7.4 eV/atom

Van der Waals forcesSoft; low melting and boiling points; solublein covalent liquids; electrical insulatorsMethane, CH

4

Ecohesive



0.1 eV/molecule

Electron gasDuctile; metallic luster; high electrical andthermal conductivitySodium, Na Ecohesive



1.1 eV/atom

bei48482_ch10.qxd 1/22/02 10:04 PM Page 349