Chapter 12 Vocabulary

Metallic Solid

Solids that are composed of metal atoms. Metallic solids are held together by a delocalized “sea” of collectively shared valence electrons

Ionic Solid

Solids that are composed of ions. Ionic solids are held together by the mutual electrostatic attraction between cations and anions

Covalent- Network Solid

Solids in which the units that make up the three-dimensional network are joined by covalent bonds Covalent-network solids are held together by an extended network of covalent bonds. responsible unique properities in semiconductors

Molecular Solid

Solids that are composed of molecules. Molecular solids are held together by the intermolecular forces we studied in Chapter 11: dispersion forces, dipole–dipole interactions, and hydrogen bonds. Because these forces are relatively weak, molecular solids tend to be soft and have low melting points.

Polymer

A large molecule of high molecular mass, formed by the joining together, or polymerization, of a large number of molecules of low molecular mass. The individual molecules forming the polymer are called monomers.

Nanomaterials

A solid whose dimensions range from 1 to 100 nm and whose properties differ from those of a bulk material with the same composition.

Crystalline Solid

A solid whose internal arrangement of atoms, molecules, or ions possesses a regularly repeating pattern in any direction through the solid.

Amorphous Solid

A solid whose molecular arrangement lacks the regularly repeating long range pattern of a crystal.

Unit Cell

The smallest portion of a crystal that reproduces the structure of the entire crystal when repeated in different directions in space. It is the repeating unit or building block of the crystal lattice

Crystal Lattice

An imaginary network of points on which the repeating motif of a solid may be imagined to be laid down so that the structure of the crystal is obtained. The motif may be a single atom or a group of atoms. Each lattice point represents an identical environment in the crystal

Motif

a group of atoms

Lattice Point

Points in a crystal all of which have identical environments.

Lattice Vectors

The vectors a, b, and c that define a crystal lattice. The position of any lattice point in a crystal can be represented by summing integer multiples of the lattice vectors. (

Primitive Lattice

A crystal lattice in which the lattice points are located only at the corners of each unit cell

Body-Centered Cubic Lattice

A crystal lattice in which the lattice points are located at the center and corners of each unit cell.

Face-Centered Cubic Lattice

A crystal lattice in which the lattice points are located at the faces and corners of each unit cell.

Alloy

A substance that has the characteristic properties of a metal and contains more than one element. Often there is one principal metallic component, with other elements present in smaller amounts. Alloys may be homogeneous or heterogeneous

Substitutional Alloy

A homogeneous (solution) alloy in which atoms of different elements randomly occupy sites in the lattice

Interstitial Alloy

An alloy in which smaller atoms fit into spaces between larger atoms. The larger atoms are metallic elements and the smaller atoms are typically nonmetallic elements

Heterogeneous Alloy

An alloy in which the components are not distributed uniformly; instead, two or more distinct phases with characteristic compositions are present.

Intermetallic Compound

A homogeneous alloy with definite properties and a fixed composition. Intermetallic compounds are stoichiometric compounds that form between metallic elements.

Electron-Sea Model

A model for the behavior of electrons in metals. which pictures the metal as an array of metal cations in a “sea” of valence electrons. The electrons are confined to the metal by electrostatic attractions to the cations, and they are uniformly distributed throughout the structure.

Semiconductor

A material that has electrical conductivity between that of a metal and that of an insulator

Insulator

Materials that do not conduct electricity

Valence Band

A band of closely spaced molecular orbitals that is essentially fully occupied by electrons

Conduction Band

A band of molecular orbitals lying higher in energy than the occupied valence band and distinctly separated from it

Band Gap

The energy gap between a fully occupied band called a valence band and an empty band called the conduction band.

Doping

Incorporation of a hetero atom into a solid to change its electrical properties. For example, incorporation of P into Si.

Holes

A vacancy in the valence band of a semiconductor, created by doping

Plastic

A material that can be formed into particular shapes by application of heat and pressure.

Thermoplastic

A polymeric material that can be readily reshaped by application of heat and pressure.

Thermosetting plastic

A plastic that, once formed in a particular mold, is not readily reshaped by application of heat and pressure.

Elastomer

A material that can undergo a substantial change in shape via stretching, bending, or compression and return to its original shape upon release of the distorting force.

Copolymer

A complex polymer resulting from the polymerization of two or more chemically different monomers.

Cross-linking

Polymers can be made stiffer by introducing chemical bonds between chains. Forming bonds between chains is called cross-linking

Vulcanization

The process of cross-linking polymer chains in rubber.