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Glossary: V


vacuum. absolute vaccuum. Compare with partial vaccuum*.
A volume which contains no matter.

The number of hydrogen atoms that typically bond to an atom of an element. For example, in H2O, oxygen has a valence of 2; carbon in CH4 has a valence of four.

valence bond.
In the valence bond theory*, a valence bond is a chemical bond formed by overlap of half-filled atomic orbitals* on two different atoms.

valence bond theory. VB theory; VB.
A theory that explains the shapes of molecules in terms of overlaps between half-filled atomic orbitals*, or half filled "hybridized" orbitals (which are a mixture of atomic orbitals).

valence electron.
Electrons that can be actively involved in chemical change; usually electrons in the shell with the highest value of n. For example, sodium's ground state* electron configuration is 1s2 2s2 2p6 3s1; the 3s electron is the only valence electron in the atom. Germanium (Ge) has the ground state electron configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p2; the 4s and 4p electrons are the valence electrons.

valence shell.
The shell* corresponding to the highest value of principal quantum number* in the atom. The valence electrons* in this shell are on average farther from the nucleus than other electrons; they are often directly involved in chemical reaction.

valence shell electron pair repulsion theory. VSEPR.
A model that explains the shapes of molecules by assuming that electron pairs arrange themselves around atoms in a way that minimizes electron-electron repulsions.

-aminoisovaleric%20acid">valine. ((CH3)2CHCH(NH2)COOH) Val; alpha-aminoisovaleric acid.
A naturally occuring aliphatic* amino acid* with a nonpolar isopropyl side chain.

van der Waals equation.
A semiempirical* equation that describes the relationship between pressure* (P), volume* (V), temperature* (T), and moles* of gas (n) for a real gas. The equation is (P + n2a/V2)(V - nb) = nRT, where a and b are constants that include the effects of molecular attractions and molecular volume. a and b are usually fitted to experimental data for a particular gas.

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.

vapor pressure. vapour pressure.
The partial pressure of a gas in equilibrium* with a condensed form (solid or liquid) of the same substance.

vapor pressure lowering. vapour pressure depression; vapor pressure depression.
A colligative property* of solutions. The vapor pressure of a solution is always lower than the vapor pressure of the pure solvent; the ratio of solution to pure solvent vapor pressures is approximately equal to the mole fraction of solvent in the solution.

variable. Compare with independent variable* and dependent variable*.
A quantity that can have many possible values. In designing experiments, variables that affect measurements must be identified and controlled. For example, an experiment that measures reaction rates must control temperature, because temperature is a variable that can change the rate of reaction.

vertical ionization energy. Compare with adiabatic ionization energy*.
The energy required to remove an electron from an atom, molecule, or ion in the gas phase without moving any nuclei. The vertical ionization energy is greater than or equal to the adiabatic ionization energy*.

vinyl. polyethylene.
A polymer* made by linking ethylene (CH2=CH2) or substituted ethylene molecules together.

viscosity. (eta) coefficient of viscosity.
The resistance a liquid exhibits to flow. Experimentally, the frictional force between two liquid layers moving past each other is proportional to area of the layers and the difference in flow speed between them. The constant of proportionality is called "viscosity" or "coefficient of viscosity", and is given the symbol eta. The time required for a liquid to drain out of a capillary tube is directly proportional to its viscosity. The poise* is a non-SI* unit frequently used to express viscosities.

visible light.
Visible light is electromagnetic radiation* with a wavelength* between 400 and 750 nm.

A substance that is critical for proper functioning of a living organism that the organism is unable to produce in sufficient quantities for itself.

volatile. volatility.
A solid or liquid material that easily vaporizes. A material with a significant vapor pressure*.

volt. (V)
The SI* unit of electrical potential. One volt equals one joule* per coulomb*.

voltage. (V)
A measured electric potential, in volts*.

voltaic cell. galvanic cell.
An electrochemical cell* that spontaneously generates electrical energy.

voltaic pile.
An early battery* consisting of disks of dissimilar metals (usually zinc and copper) separated by moist paper or cloth soaked in an electrolyte* solution.

An instrument for measuring voltages* and amperages*.

volume. (V)
1. The amount of space an object takes up. 2. The amount of space a container can hold. The SI unit of volume is the cubic meter (m3); the liter* is a popular unit of volume in chemistry.

volume percentage. ((v/v)%)
Volume percentages express the concentration of a component in a mixture or an element in a compound. For example, 95% ethanol by volume contains 95 mL of ethanol in 100 mL of solution (NOT in 100 mL of water!)

vulcanization. vulcanization of rubber.
A process of combining rubber with sulfur or other substances that causes the polymer* chains to crosslink, making them stronger and more elastic.


General Chemistry Online! Glossary: V

Copyright © 1997-2010 by Fred Senese
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Last Revised 08/17/15.URL: http://antoine.frostburg.edu/chem/senese/101/glossary/v.shtml