Key Terms

adhesive force

force of attraction between molecules of different chemical identities

amorphous solid

(also, noncrystalline solid) solid in which the particles lack an ordered internal structure

body-centered cubic (BCC) solid

crystalline structure that has a cubic unit cell with lattice points at the corners and in the center of the cell

body-centered cubic unit cell

simplest repeating unit of a body-centered cubic crystal; it is a cube containing lattice points at each corner and in the center of the cube

boiling point

temperature at which the vapor pressure of a liquid equals the pressure of the gas above it

Bragg equation

equation that relates the angles at which X-rays are diffracted by the atoms within a crystal

capillary action

flow of liquid within a porous material due to the attraction of the liquid molecules to the surface of the material and to other liquid molecules

Clausius-Clapeyron equation

mathematical relationship between the temperature, vapor pressure, and enthalpy of vaporization for a substance

cohesive force

force of attraction between identical molecules

condensation

change from a gaseous to a liquid state

coordination number

number of atoms closest to any given atom in a crystal or to the central metal atom in a complex

covalent network solid

solid whose particles are held together by covalent bonds

critical point

temperature and pressure above which a gas cannot be condensed into a liquid

crystalline solid

solid in which the particles are arranged in a definite repeating pattern

cubic closest packing (CCP)

crystalline structure in which planes of closely packed atoms or ions are stacked as a series of three alternating layers of different relative orientations (ABC)

deposition

change from a gaseous state directly to a solid state

diffraction

redirection of electromagnetic radiation that occurs when it encounters a physical barrier of appropriate dimensions

dipole-dipole attraction

intermolecular attraction between two permanent dipoles

dispersion force

(also, London dispersion force) attraction between two rapidly fluctuating, temporary dipoles; significant only when particles are very close together

dynamic equilibrium

state of a system in which reciprocal processes are occurring at equal rates

face-centered cubic (FCC) solid

crystalline structure consisting of a cubic unit cell with lattice points on the corners and in the center of each face

face-centered cubic unit cell

simplest repeating unit of a face-centered cubic crystal; it is a cube containing lattice points at each corner and in the center of each face

freezing

change from a liquid state to a solid state

freezing point

temperature at which the solid and liquid phases of a substance are in equilibrium; see also melting point

hexagonal closest packing (HCP)

crystalline structure in which close packed layers of atoms or ions are stacked as a series of two alternating layers of different relative orientations (AB)

hole

(also, interstice) space between atoms within a crystal

hydrogen bonding

occurs when exceptionally strong dipoles attract; bonding that exists when hydrogen is bonded to one of the three most electronegative elements: F, O, or N

induced dipole

temporary dipole formed when the electrons of an atom or molecule are distorted by the instantaneous dipole of a neighboring atom or molecule

instantaneous dipole

temporary dipole that occurs for a brief moment in time when the electrons of an atom or molecule are distributed asymmetrically

intermolecular force

noncovalent attractive force between atoms, molecules, and/or ions

interstitial sites

spaces between the regular particle positions in any array of atoms or ions

ionic solid

solid composed of positive and negative ions held together by strong electrostatic attractions

isomorphous

possessing the same crystalline structure

melting

change from a solid state to a liquid state

melting point

temperature at which the solid and liquid phases of a substance are in equilibrium; see also freezing point

metallic solid

solid composed of metal atoms

molecular solid

solid composed of neutral molecules held together by intermolecular forces of attraction

normal boiling point

temperature at which a liquid’s vapor pressure equals 1 atm (760 torr)

octahedral hole

open space in a crystal at the center of six particles located at the corners of an octahedron

phase diagram

pressure-temperature graph summarizing conditions under which the phases of a substance can exist

polarizability

measure of the ability of a charge to distort a molecule’s charge distribution (electron cloud)

simple cubic structure

crystalline structure with a cubic unit cell with lattice points only at the corners

simple cubic unit cell

(also, primitive cubic unit cell) unit cell in the simple cubic structure

space lattice

all points within a crystal that have identical environments

sublimation

change from solid state directly to gaseous state

supercritical fluid

substance at a temperature and pressure higher than its critical point; exhibits properties intermediate between those of gaseous and liquid states

surface tension

energy required to increase the area, or length, of a liquid surface by a given amount

tetrahedral hole

tetrahedral space formed by four atoms or ions in a crystal

triple point

temperature and pressure at which the vapor, liquid, and solid phases of a substance are in equilibrium

unit cell

smallest portion of a space lattice that is repeated in three dimensions to form the entire lattice

vacancy

defect that occurs when a position that should contain an atom or ion is vacant

van der Waals force

attractive or repulsive force between molecules, including dipole-dipole, dipole-induced dipole, and London dispersion forces; does not include forces due to covalent or ionic bonding, or the attraction between ions and molecules

vapor pressure

(also, equilibrium vapor pressure) pressure exerted by a vapor in equilibrium with a solid or a liquid at a given temperature

vaporization

change from liquid state to gaseous state

viscosity

measure of a liquid’s resistance to flow

X-ray crystallography

experimental technique for determining distances between atoms in a crystal by measuring the angles at which X-rays are diffracted when passing through the crystal