Crystallography

Refers to the special arrangement of atoms that extends only to the atom's nearest neighbors.

Short-Range Order

Refers to the special atomic arrangement that extends over length scales of 10 nanometers.

Long-Range Order

A material in which the atoms are arranged in a repeating or periodic array over large atomic distances.

Crystalline Solid

Exhibits only a short-range order of atoms or ions.

Amorphous Solid

Typically forms in ceramic and polymer systems.

Glass

Composed of relatively large chains of polymer molecules that get entangled with each other.

Plastic

Atoms are thought of as being solid spheres representing nearest neighbor atoms touching one another.

Atomic Hard-Sphere Model

A collection of plane lattices.

Unit Mesh

Lattice nodes occur only at their corners.

Primitive (p) Unit Mesh

Lattice nodes occur at the center.

Centered (c) Unit Mesh

Refers to a point in a unit mesh that represents one particle.

Lattice Node

Refers to the collection of lattice points.

Plane Lattice

Refers to the basic structural unit of a crystalline solid that represents crystal symmetry of a crystal structure.

Unit Cell

Refers to the axial lengths or dimensions of the unit cell.

Lattice Parameters

Refers to the unique three-dimensional arrangements of lattice points named after Auguste Bravais.

Bravais Lattices

a0=2r, where a0 is the side length and r is the atomic radius.

Simple Cubic Structure (Primitive Lattice)

a0 = 4r/sqrt(3).

Body-Centered Structure

a0 = 4r/sqrt(2).

Face-Centered Structure

c0 /a0 = sqrt(8/3) = 1.633.

Hexagonal Close-Packed Structure

Refers to the number of atoms touching a particular atom or the number of nearest neighbors.

Coordination Number

Refers to the fraction or space occupied by atoms.

Atomic Packing Factor

Mass over volume.

Density

Refers to the scattering of X-rays by the units of a crystalline solid.

X-ray Diffraction

Recommended that since the wavelength of X-rays is comparable in magnitude to the distances between lattice points in a crystal, the lattice should be able to diffract X-rays.

Max von Laue

Produce an X-ray diffraction pattern.

Interference

Constructive Interference

Destructive Interference

The process by which a beam of X-rays is directed at a mounted crystal and atoms in the crystal absorb some of the incoming radiation and then reemit it.

Scattering of X-rays

Determines the angles of coherent and incoherent scattering from a crystal lattice.

Bragg's Law

Tells the relative electron densities at various locations in a molecule.

Electron-Density Contour Map

Composed of charged species and have high melting points. It is not a conductor of electricity when in solid state but in a liquid.

Ionic Crystals

The higher the lattice energy, the more stable the compound.

Lattice Energy

Exist when atoms are held together in an extensive three-dimensional network altogether by covalent bonds.

Covalent Crystals

Refers to the arrangement of atoms in a crystal structure based on temperature and pressure.

Allotropy

Each carbon is tetrahedrally bonded to four other carbon atoms and it has a melting point of 3550 degrees Celsius.

Diamond

A good conductor of electricity in directions along the planes of carbon atoms.

Graphite

Has a similar arrangement to that of carbon in diamond. Similar to diamond in many aspects because of its hardness and melting point of 1610 degrees Celsius.

Quartz (SiO2)

The lattice points are occupied by molecules that have Van der Waals forces and/or hydrogen bonding.

Molecular Crystals

Refers to a general term used to define the attraction of intermolecular forces between molecules.

Van der Waals Forces

Instantaneous Dipole.

Weak London Dispersion Forces

Occur in molecules that are permanently polar.

Dipole-Dipole Forces

The molecules are packed together as closely as their size and shape allow. Most molecular crystals melt at temperatures below 100 degrees Celsius.

Molecular Crystals

Have the simplest structure because every lattice point in the crystal is occupied by an atom of the same metal.

Metallic Crystals

Lack a regular three-dimensional arrangement of atoms.

Amorphous Solids

An optically transparent fusion product of inorganic materials that has cooled to a

Glass

the chief component of glass

Silicon Dioxide

because of the presence of metal ions as oxides - impurities

Color of the Glass

contains Fe2O3 or CuO

Green Glass

contains UO2

Yellow Glass

CoO and CuO

Blue Glass

contains small particles of gold and copper

Red Glass

operation performed on an object which leaves it in a configuration that is indistinguishable from and superimposable on the original configuration

Symmetry Operation

refers to the symmetry operation that is carried out with respect to points, lines, or planes.

Symmetry Element