Glossary: Solids

allomer. allomerism.

Substances with different chemical composition but the same crystalline form.

amorphous. amorphous solid. Compare with crystal.

A solid that does not have a repeating, regular three-dimensional arrangement of atoms, molecules, or ions.

crystal.

A sample of a crystalline solid that has a regular shape bound by plane surfaces (facets) that intersect at characteristic angles. The shape results from the arrangement of the substances atoms, ions, or molecules. Most crystals contain defects that can strongly affect their optical and electrical properties.

crystalline solid. crystalline. Compare with amorphous.

A solid that has a repeating, regular three-dimensional arrangement of atoms, molecules, or ions.

enthalpy of sublimation. (H_sub) heat of sublimation.

The change in enthalpy when one mole of solid vaporizes to form one mole of gas. Enthalpies of sublimation are always positive because vaporization involves overcoming most of the intermolecular attractions in the sublimation.

freezing point. (mp) standard melting point; normal melting point; melting point.

The temperature at which the vapor pressure of a liquid is equal to the vapor pressure of the corresponding solid form. The liquid and solid forms can coexist at equilibrium at the freezing point. The standard melting point is the melting point at standard pressure.

lattice.

A regular array of ions or atoms.

network covalent solid. network covalent substance.

A substance which consists of an array of atoms held together by an array of covalent bonds. A crystal of a network covalent solid is actually a single, gigantic molecule. Diamond and quartz are examples.

perfect crystal.

A crystal with no defects or impurities, made of completely identical repeating subunits. Further, a perfect crystal has only one possible arrangement of subunits, with every subunit making exactly the same contribution to the total energy of the crystal.

solid.

A solid is a relatively dense, rigid state of matter, with a definite volume and shape. Molecules in solids are often packed close together in regularly repeating patterns, and vibrate around fixed positions.

unit cell.

The simplest arrangement of atoms or molecules that regularly repeats in a crystal structure.

van der Waals force.

A force acting between nonbonded atoms or molecules. Includes dipole-dipole, dipole-induced dipole, and London forces.

van der Waals radius. van der Waals radii.

One half the distance between two nonbonded atoms, when attractive and repulsive forces between the atoms are balanced.

x-ray crystallography.

Determination of three dimensional arrangement of atoms in a crystal by analysis of x-ray diffraction patterns.

Copyright © 1997-2010 by Fred Senese
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Last Revised 02/23/18.URL: http://antoine.frostburg.edu/chem/senese/101/solids/glossary.shtml