Chapter 12: Intermolecular Forces (Liquids, Solids, and Phase Changes)

Kent State, THE Scott Bunge

amorphous solid

A solid that has a poorly defined shape because its particles do not have an orderly arrangement throughout a sample.

atomic solid

A solid consisting of individual atoms held together by dispersion forces; the frozen noble gases are the only examples.

band theory

An extension of molecular orbital (MO) theory that explains many properties of metals and other solids—in particular, the differences in conductivity of metals, metalloids, and nonmetals.

body-centered cubic unit cell

A unit cell in which a particle lies at each corner and in the center of a cube.

boiling point

The temperature at which the vapor pressure inside bubbles forming in a liquid equals the external (atmospheric) pressure.

branch

A side chain appended to a polymer backbone or to the longest sequence of atoms in an organic compound.

capillarity

(alsocapillary action) The rising of a liquid through a narrow space against the pull of gravity.

ceramic

A nonmetallic, nonpolymeric solid that is hardened by heating it to high temperatures and, in most cases, consists of silicate microcrystals suspended in a glassy cementing medium.

Clausius-Clapeyron equation

An equation that expresses the linear relationship between vapor pressurePof a liquid and temperatureT; in two-point form, it is

condensation

The process of a gas changing into a liquid.

conduction band

In band theory, the empty, higher energy portion of the band of molecular orbitals into which electrons move when conducting heat and electricity.

conductor

A substance (usually a metal) that conducts an electric current well.

coordination number

In a crystal, the number of nearest neighbors surrounding a particle. In a complex ion, the number of ligand atoms bonded to the central metal ion.

copolymer

A polymer that consists of two or more types of monomer.

critical point

The point on a phase diagram above which the vapor cannot be condensed to a liquid; the end of the liquid-gas curve.

crosslink

A branch that covalently joins one polymer chain to another.

crystal defect

Any of a variety of disruptions in the regularity of a crystal structure.

crystalline solid

A solid with a well-defined shape because of the orderly arrangement of the atoms, molecules, or ions.

cubic closest packing

A crystal structure based on the face-centered cubic unit cell in which the layers have anabcabc. . . pattern.

degree of polymerization (n)

The number of repeat units in a polymer chain.

deposition

The process of changing directly from a gas to a solid.

dipole-dipole force

The intermolecular attraction between oppositely charged poles of nearby polar molecules.

dispersion force

(alsoLondon force) The intermolecular attraction between all particles as a result of instantaneous polarizations of their electron clouds; the intermolecular force primarily responsible for the condensed states of nonpolar substances.

doping

Adding small amounts of other elements into the crystal structure of a semiconductor to enhance a specific property, usually conductivity.

elastomer

A polymeric material that can be stretched and springs back to its original shape when released.

face-centered cubic unit cell

A unit cell in which a particle occurs at each corner and in the center of each face of a cube.

freezing

The process of cooling a liquid until it solidifies.

heat of fusion (ΔH^°_fus)

(alsoenthalpy of fusion) The enthalpy change occurring when 1 mol of a solid substance melts; designated (ΔH^°_fus) at the standard state.

heat of sublimation

(alsoenthalpy of sublimation) The enthalpy change occurring when 1 mol of a solid substance changes directly to a gas. The sum of the heats of fusion and vaporization; designated (ΔH^°_subl) at the standard state.

heat of vaporization

(alsoenthalpy of vaporization) The enthalpy change occurring when 1 mol of a liquid substance vaporizes; designated (ΔH^°_vap) at the standard state.

heating-cooling curve

A plot of temperature vs. time for a sample when heat is absorbed or released at a constant rate.

hexagonal closest packing

A crystal structure based on the hexagonal unit cell in which the layers have anabab. . . pattern.

hydrogen bond (H bond)

A type of dipole-dipole force that arises between molecules that have an H atom bonded to a small, highly electronegative atom with lone pairs, usually N, O, or F.

insulator

A substance (usually a nonmetal) that does not conduct an electric current.

intermolecular forces

(alsointerparticle forces) The attractive and repulsive forces among the particles—molecules, atoms, or ions—in a sample of matter.

ion-dipole force

The intermolecular attractive force between an ion and a polar molecule (dipole).

ionic solid

A solid whose unit cell contains cations and anions.

lattice

The three-dimensional arrangement of points created by choosing each point to be at the same location within each particle of a crystal; thus, the lattice consists of all points with identical surroundings.

liquid crystal

A substance that flows like a liquid but packs like a crystalline solid at the molecular level.

melting

(alsofusion) The change of a substance from a solid to a liquid.

melting point

The temperature at which the solid and liquid forms of a substance are at equilibrium.

metallic solid

A solid whose individual atoms are held together by metallic bonding.

molecular solid

A solid held together by intermolecular forces between individual molecules.

monomer

A small molecule, linked covalently to others of the same or similar type to form a polymer; the repeat unit of the polymer.

nanotechnology

The science and engineering of nanoscale systems (size range of 1–100 nm).

network covalent solid

A solid in which all the atoms are bonded covalently so that individual molecules are not present.

packing efficiency

The percentage of the total volume occupied by atoms, ions, or molecules in a unit cell.

phase

A physically distinct and homogeneous part of a system.

phase change

A physical change from one phase to another, usually referring to a change in physical state.

phase diagram

A diagram used to describe the stable phases and phase changes of a substance as a function of temperature and pressure.

plastic

A material that, when deformed, retains its new shape.

polarizability

The ease with which a particle’s electron cloud can be distorted.

polymer

(alsomacromolecule) An extremely large molecule that results from the covalent linking of many simpler molecular units (monomers).

radius of gyration (R_g)

A measure of the size of a coiled polymer chain, expressed as the average distance from the center of mass of the chain to its outside edge.

random coil

The shape adopted by most polymer chains and caused by random rotation about the bonds joining the repeat units.

semiconductor

A substance whose electrical conductivity is poor at room temperature but increases significantly with rising temperature.

simple cubic unit cell

A unit cell in which a particle occupies each corner of a cube.

sublimation

The process by which a solid changes directly into a gas.

superconductivity

The ability to conduct a current with no loss of energy to resistive heating.

surface tension

The energy required to increase the surface area of a liquid by a given amount.

triple point

The pressure and temperature at which three phases of a substance are in equilibrium. In a phase diagram, the point at which three phase-transition curves meet.

unit cell

The smallest portion of a crystal that, if repeated in all three directions, yields the crystal.

valence band

In band theory, the lower energy portion of the band of molecular orbitals, which is filled with valence electrons.

van der Waals radius

One-half of the closest distance between the nuclei of identical nonbonded atoms.

vapor pressure

The pressure exerted by a vapor at equilibrium with its liquid in a closed system.

vaporization

The process of changing from a liquid to a gas.

viscosity

A measure of the resistance of a fluid to flow.