Chemistry - A Molecular Science

Glossary

U

The

uncertainty principle

states that it is impossible

to know both the position and speed of subatomic particles to high accuracy. In order to measure one more accurately, you most lose accuracy in the other.

A

unimolecular

process involves only one particle.

A

unit cell

is the simplest arrangement of particles that

generates the entire lattice when translated in all three dimensions.

Unsaturated

carbon atoms are involved in less than

four sigma bonds.

V

The

valence band

is the highest energy filled band

containing the valence electrons of a metal.

In

valence bond theory

, bonds arise from the overlap

of orbitals on adjacent atoms. The orbitals can be either atomic or hybridized.

Valence electrons

are those outermost electrons that

dictate the properties of th

e atom and are involved

in chemical bonding. They reside in the outermost s sublevel and any unfilled sublevels.

Valence-shell electron-pair repulsion (VSEPR)

theory is used to explain molecular shapes in terms of electron regions adopting the spatial orientation that minimizes the elect

ron-electron repulsions

between them.

The

Van’t Hoff factor (

i) relates the colligative

concentration to the concentration of the solute. For example, m

= c

im.

The

van der Waals radius

is one-half of the distance

between identical, nonbonded atoms in a crystal. Atoms that are closer than the sum of their van der Walls radii are assumed to be interacting.

Vaporization

is the process by which a liquid is

converted into its vapor.

The

vapor pressure

of a liquid is the pressure of its

vapor in equilibrium with the liquid at a given temperature.

Vapor pressure lowering (

ΔP)

is amount by which the

vapor pressure of a solvent is reduced by the addition of a volatile solute.

Vibrational degrees of freedom

of a molecule are the

relative motions of its atoms that result in small oscillating changes in bond lengths and angles.

Viscosity

is the resistance of a liquid to flow.

Void space

is unoccupied space.

The

volt

is the SI unit of electrical potential.

1 V = 1 J

.C

-1.

W

The

wave function

of an electron is a function that

contains all of the information about the electron.

The

wavelength (

) is the distance between two λ

corresponding points on a wave.

Wave-particle duality

is a term used to indicate that

photons (light) and very small particles, such as electrons, behave as both particles and waves.

A

weak acid

is an acid that does not react extensively

with water,

i.e

., it is an acid with a dissociation

constant that is much less than one.

A

weak base

is a substance that reacts only slightly

with water to produce hydroxide ions.

A

weak electrolyte

is a substance whose aqueous

solution conducts only a small current of electricity because only a small fraction of weak electrolyte molecules produce ions in water.

Work (

w)

is a force through a distance,

w = fd. Thus,

something must move, and there must be a resistance to the movement in order for work to be done. By definition, the symbol

w is the work done

ON the system, and -

w is the work done BY the

system.

X

X-ray diffraction

is a technique in which x-rays are

scattered from atoms in the solid to determine the distances between the atoms

and ions in the crystal.

Z

Zeolites

are aluminosilicates built from tetrahedral

AlO

and SiO 4

units bridged by oxygen atoms. 4

They are filled with ch

annels and pores, which

provide many uses for the material.

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North

Carolina

State

University