The Handy Chemistry Answer Book (2014)

absolute zero—lowest theoretical temperature; (0.00 K, −273.15 °C, −459.67 °F)

absorption—capture of one material into another; can be a physical or chemical process

accuracy—closeness of a measurement to the actual or accepted value

acid—a molecule that has easily removable hydrogen ions (Brønsted-Lowry acid), can accept a pair of electrons (Lewis), or releases hydrogen ions in solution (Arrhenius)

actactic polymer—a polymer in which the chiral centers are arranged randomly along the chain

actinide—elements 89–102

activation energy—difference in energy between the reactants and transition state (or activated complete) for a chemical reaction or process

adiabatic—a process that does not absorb or release energy

adsorption—capture of one material onto the surface of another

aerosol—suspension of a solid or a liquid in a gas (e.g., smoke, fog)

aliquot—a sample taken from a larger amount of a material

alkali—a basic substance (i.e., pH > 7)

alkali metal—Group 1 of the periodic table (i.e., Li, Na, K, Rb, Cs, Fr)

alkali earth metal—Group 2 of the periodic table (i.e., Be, Mg, Ca, Sr, Ba, Ra)

alkane—a hydrocarbon with the formula C_nH_2n+2 (i.e., no double bonds)

alkene—a hydrocarbon at least one double bond

allotrope—different arrangements of atoms of a single element (e.g., diamond and graphite are allotropes of carbon)

alloy—a mixture of metals (e.g., bronze, a mixture of zinc and copper)

alpha particle—a particle consisting of two neutrons and two protons (i.e., a helium nucleus)

amalgam—an alloy of mercury

amorphous—a solid without a repeating, ordered structure

amplitude—the height (or maximum displacement) of a wave

angstrom—a unit of length used often to describe bond lengths; 1 Å = 10⁻¹⁰ m

anhydrous—without water

anion—a negatively charged ion

anode—the electrode at which oxidation occurs

antibonding orbital—orbitals in which the component atomic orbitals are out of phase, leading to repulsion or destabilization

atom—smallest unit of a chemical element

atomic number—number of protons in an atom

atomic orbital—an equation that describes the probability of finding an electron around a nucleus

atomic radius—half the distance between nuclei of the same element

atomic weight—the average mass of an atom of a given element

Avogadro’s number—the number of particles in one mole, 6.022 × 1023

azeotrope—a mixture that does not change composition during distillation

band gap—the energy range separating the top of the valence band and the bottom of the conduction band in a semiconductor

barometer—an instrument used to measure pressure

base—a compound that accepts hydrogen ions (Brønsted-Lowry acid), has a pair of available electrons (Lewis), or releases hydroxide ions in solution (Arrhenius)

beta particle—an electron created during nuclear decay reactions

bimolecular reaction—a reaction that involves two molecules in the rate-determining transition state

black body radiation—electromagnetic radiation given off by a black body; at room temperature most of this radiation is in the infrared, but at higher temperatures visible light can be emitted

boiling point—temperature for a given liquid at which its vapor pressure is equal to the external pressure acting on it

boiling point elevation—a colligative property, the increase in boiling point of a liquid as a solute is added

bond angle—the angle relating the orientation of two bonds connecting three atoms

bond length—the distance separating two chemically bonded atoms

bond order—number of pairs of electrons shared by two atoms

bond strength—a measure of the energy required to break a chemical bond

bonding orbital—a molecular orbital that is more stable than the atomic orbitals that were combined to generate it

Boyle’s law—law stating that the pressure and volume of gas are inversely proportional

brass—an alloy of copper and zinc, the relative percentages of the two species may vary

bronze—an alloy of copper and tin, with copper as the primary component

buffer—a solution that tends to resist changes in pH upon addition of an acid or base

calorie—a unit of energy equal to 4.184 Joules

calorimeter—a tool used to measure the heat change associated with a chemical reaction

carbanion—an anion in which a carbon atom bears a significant fraction of the negative charge

carbocation—a cation in which a carbon atom bears a significant fraction of the positive charge

carbohydrate—organic compounds of carbon, hydrogen, and water, typically with hydrogen and oxygen in a 2:1 ratio, respectively, these are often called sugars

catalyst—any substance that increases the rate of a chemical reaction without being consumed by the reaction

cathode—electrode where reduction occurs

cation—a positively charged ion

Celsius—common temperature scale in which the melting and boiling points of water are defined to be 0 °C and 100 °C, respectively

ceramic—an inorganic crystalline solid typically prepared by heating

chalcogen—a group 16 element (oxygen, sulfur, selenium, tellurium, polonium, or livermorium)

Charles’s Law—a law stating that the volume and temperature of a gas are directly proportional

chelation—binding of a ligand to a metal atom through two or more positions

chemical bond—sharing of electrons between two or more atoms

chemical change—a process that alters the arrangement of atoms in a substance

chemiluminescence—emission of light resulting from a chemical reaction

chiral center—an atom whose arrangement of substituents is non-superimposable with its mirror image

chirality—a geometric property of a molecule whose mirror image is non-superimposable

with the original molecule

chromatography—a process to separate mixtures, generally by differing affinities of to a solid stationary phase

colligative properties—properties of a solution that depend on the amount of solute dissolved

collision frequency—average number of collision events per second

collision theory—defines reaction rates as a function of the collision frequency

colloid—suspension of particles of one substance in another (e.g., milk)

combustion—a chemical reaction between a fuel and an oxidant to produce heat

compound—a substance composed of more than one element

condensation—conversion of a gas into a liquid

condensation reaction—a reaction in which two molecules combine to form one larger molecule, with the concurrent loss of another small molecule like water or HCl

congener—elements in the same group of the periodic table

coordination number—the number of bonds to an atom

copolymer—a polymer of two or more monomers

coulomb—the standard unit of charge, defined as the amount of charge delivered by 1 amp in 1 second

Coulomb’s Law—law describing the force between a pair of charged particles separated by a distance

covalent bond—the equal, or near equal, sharing of electrons between two or more atoms

critical point—a set of conditions at which no boundary exists between two phases of a substance

crystal—a solid with an ordered arrangement of atoms of molecules

crystal field theory—a model used to describe the electronic structure of transition metal molecules, particularly the energy of the d orbitals

crystallization—formation of crystals from a solution of the compound, often used as a purification technique

Curie point—the temperature at or beyond which a ferromagnetic material becomes paramagnetic

d orbital—an atomic orbital with an angular momentum quantum number of 2

Dalton’s Law—a law regarding partial pressures of gases that states the total pressure of a mixture of gases is equal to the sum of the partial pressures of each individual component

dative bond—a chemical bond in which one atom is essentially providing both electrons involved in the bond

de Broglie wavelength—also known as matter wavelength; inversely proportional to the momentum of the object or particle; see also wave-particle duality

decant—to pour off a liquid from a solid sediment

decay rate—rate at which a nucleus emits a particle

degenerate orbitals—atomic or molecular orbitals of equal energy

density—mass per unit volume of a given substance

dependent variable—a variable that changes as a function of the independent variable

dextrorotatory—having the property of rotating plane polarized light clockwise

diamagnetic—a material that creates an opposing electric field in response to an applied electric field

diastereomer—a stereoisomer that is not an enantiomer

diffraction—change in the direction of a wave caused by an obstacle (be it a wall, or a nucleus)

diffusion—spreading of something more widely; the movement of a substance from an area of high concentration to an area of lower concentration; the scattering of waves through a space or an object

dilution—process that lowers the concentration of a substance

dipole—a molecule or a property of a molecule that involves the separation of positive charge from negative charge

distillation—a purification technique that separates substances based on their differences in boiling points

DNA—an acronym for deoxyribonucleic acid, which is the biomolecule that stores genetic information in organisms

ductile—pliable, not brittle; a metal that can be drawn into a thin wire

elastic material—a material that deforms when an external force is applied, but returns to its original shape when the external forces are removed

electrochemical cell—a device that either produces an electric current from or uses an electric current to drive a redox reaction

electrolysis—use of an electric current to drive a redox reaction

electrolyte—a substance that forms ions in a solution

electron—fundamental particle with a negative electric charge

electron affinity—the energy change upon adding an electron to a neutral species

electronegativity—a measure describing how strongly atoms attract electrons

electronic wave function—a mathematical description used to describe the electrons in a chemical system

electrophile—a species that is attracted to electron-rich atoms or molecules

element—atoms with the same atomic number

elementary reaction—single step in a chemical reaction

elimination reaction—a reaction in which two ligands or substituents are removed from a molecule

empirical formula—the relative ratios of elements in a substance

emulsion—the suspension of a liquid in another liquid, a type of colloid

enantiomer—non-superimposable mirror images

endothermic—a process or reaction that absorbs heat

enthalpy—for a reaction the heat absorbed or released is defined as the change in enthalpy

entropy—a measure of the disorder, or dispersion of energy, in a system; the 2nd Law of Thermodynamics states that a spontaneous change cannot decrease the entropy of an isolated system

enzyme—a protein-based molecule that acts as a catalyst

equilibrium—a state in which a chemical reaction and its reverse are proceeding at equal rates

evaporation—conversion of a liquid into a gas

excited state—an atom or molecule in any electronic state of higher energy than its lowest energy state

exothermic—a process or reaction that releases heat

extensive property—a property that depends on the amount of a substance present (e.g., size, mass, volume)

extraction—removal of one or more substances from a mixture, typically based on differing solubility of a substance in a solvent

filtration—the process of removing any solid particulates from a solution

fission—a nuclear reaction in which a nucleus splits into smaller parts

flash point—temperature at which the vapor pressure of a liquid is high enough that the vapor can be ignited

formal charge—the amount of charge (typically in integer units of electron charge) assigned to a specific atom in a molecule

freezing point—temperature at which liquid and solid phases coexist in equilibrium

freezing point depression—decrease in freezing point for a solution from that of a pure solvent

frequency—rate of an event per unit time

fuel cell—device that converts chemical energy to electrical energy

fusion—the joining of two (or more) atoms

galvanization—application of a thin layer of zinc metal to steel or iron, which prevents the formation of rust

gamma radiation—high frequency electromagnetic radiation; can be dangerous to living things

gel—a semisolid suspension of a solid in a liquid, a type of colloid

geometric isomer—a molecule with the same molecular formula but different arrangement of those atoms in space

glass—an amorphous solid material

glass transition—transition observed in amorphous materials between a hard material and a more liquid- or rubber-like state

gram—1/1000 of a kilogram, which is the standard unit for mass

ground state—lowest energy state for an atom or molecule

half life—the amount of time required to consume half of the initial amount of a reactant

halogen—elements in group 18 (group VIIA)

hapticity—number of contiguous atoms coordinated to a central atom

heat—transfer of energy between substances with different temperatures

heat capacity—the amount of heat required to raise the temperature of an object by 1 °C

Henderson-Hasselbach equation—equation for pH of a solution as a function of acid strength (pKa); pH = pK_a + log₁₀ ([A⁻]/[HA])

Henry’s Law—equation relating the pressure of a gas to its solubility in a liquid

Hess’s Law—states that the change in enthalpy for a reaction that occurs in multiple steps is equal to the sum of the change in enthalpy for each step; related to the 1st Law of Thermodynamics

heteroatom—any atom other than carbon or hydrogen

heterogeneous mixture—a sample containing more than one substance

homogeneous mixture—a sample containing only one, pure substance

hybrid orbital—an orbital that is composed of multiple atomic orbitals (e.g., sp3 hybrid orbital)

hydrogen bond—interaction between a hydrogen atom bonded to a highly electronegative atom and a Lewis basic atom

hydrolysis—the breaking of chemical bond(s) by the addition of water to a molecule

hydrophilic—a molecule that interacts favorably with or is attracted to water, typically via hydrogen bonding or other dipolar interactions

hydrophobic—a nonpolar molecular that does not interact with water

hygroscopic—a substance that readily absorbs water from its surroundings

ideal gas law—an equation that approximates the properties of gases, commonly written as: PV = nRT (where, P = pressure, V = volume, n = number of moles, R = gas constant, T = temperature)

immiscible—unmixable liquids (e.g., oil and water)

independent variable—a variable that is set to a specific, known value in an experiment

indicator—a substance that undergoes an observable change in response to a chemical input (e.g., pH, redox, presence of a metal ion)

inductive effect—polarization of a chemical bond due to transmission of charge through other chemical bonds

infrared—electromagnetic radiation with wavelengths of 750 nm to 1 mm, just longer than the visible spectrum, but not as long as microwave radiation

insoluble—a substance that does not dissolve in a solvent

intensive property—a property that does not depend on the amount of a substance present (e.g., density, temperature, color)

interference—superposition of two or more waves, resulting in either higher (constructive) or lower (destructive) amplitude

ion—a charged atom or molecule

ionic bond—attraction between two oppositely charged ions

ionization energy—energy required to remove an electron from an atom or ion (i.e., ionization potential)

irreversible reaction—a reaction in which the products cannot be converted back into the reactants

isobaric—with constant pressure

isomer—molecules with different arrangement of atoms in space, but the same molecular formula

isotactic polymer—a polymer in which all substituents are located on the same side of the backbone

isothermal—with constant temperature

isotope—atoms of the same element (same number of protons) with different number of neutrons

kelvin—standard temperature scale in which the triple point of water is defined at 273.16 Kelvin

kilogram—standard base unit of mass

kinase—an enzyme that catalyzes phosphorylation (transfer of a phosphate group)

kinetic energy—energy of an object due to its motion

kinetics—the rate of chemical reactions or processes

lathanide—elements 57–70

lattice—a regular array of atoms or ions

Le Chatelier’s Principle—states that any change (concentration, pressure, temperature, volume) to a chemical system at equilibrium will cause the equilibrium to shift in order to counteract that change

levorotatory—having the property of rotating plane polarized light counterclockwise

Lewis acid—a molecule that can accept a pair of electrons

Lewis base—a molecular that can donate a pair of electrons

Lewis structure—a writing convention in which valence electrons are represented as dots and chemical bonds are represented by lines between atom

ligand—a group (an ion or a molecule) that coordinates to a metal atom, forming a coordination complex

lipid—a biochemical molecule that is hydrophobic or amiphilic (e.g., waxes, fats, vitamins A, D, E, K, glycerides, etc.)

liquid—a state of matter with a defined volume, but no fixed shape

London dispersion force—a weak repulsive interaction between molecules resulting from interactions of electron clouds

lone pair—a pair of valence electrons that are localized on a single atom (i.e., not involved in bonding)

magnetic quantum number—the third quantum number, m, which describes the direction of the electron’s angular momentum

main group elements—elements of the s and p blocks in the periodic table

malleable—a material that can be pressed into shapes or sheets without breaking or cracking

manometer—an instrument used to measure pressures of gases

mass—the resistance of an object to acceleration; commonly used interchangeably with weight, though the latter depends on gravity while the former does not

matter—any substance that has mass

melting point—temperature at which liquid and solid phases coexist in equilibrium

meniscus—a phase boundary, which is curved due to surface tension

meta—term used to describe two substituents on an aromatic ring that are separated by one position (i.e., 1,3-subsituted)

metal—an element, compound, or alloy that is a good conductor of heat and electricity, also usually reflective, ductile, and malleable

metalloid—an element, compound, or alloy that has metallic and nonmetallic properties

microwave—electromagnetic radiation with wavelengths of 1 millimeter to 1 meter, just longer than infrared radiation, but not as long as radio waves

miscible—liquids that when mixed form a single phase

mixture—a system composed of two or more difference substances

molality—a measure of concentration defined as moles of solute per kilogram of solvent

molarity—a measure of concentration defined as moles of solute per liter of solvent

mole—the SI unit used to describe the amounts of chemical; 6.023 × 1023

mole fraction—the amount of a substance in moles divided by the total number of moles present

molecular formula—the type and number of atoms in a molecule; unlike empirical formula, the ratios are not reduced

molecular orbital—a mathematical equation describing the position of an electronic in a molecule

monodentate—a ligand that coordinates to a central atom via only one atom (compare with chelate)

monomer—a group of atoms that forms the repeating unit in a polymer

natural abundance—relative abundance of different isotopes of an element found on Earth (i.e., not produced in a lab)

Nernst equation—an equation describing the potential of an electrochemical half-cell

neutron—an uncharged, subatomic particle found in the nucleus of an atom

noble gas—Group 18 of the periodic table, characterized by their general inertness due to their complete valence shell of electrons

noble gas core—used to abbreviate an atom’s electron configuration (e.g., the electron configuration of nitrogen is: 1s² 2s² 2p³, which can be abbreviated [He] 2s² 2p³)

nonmetal—an element that does not possess the properties of a metal

nonpolar—a molecule in which the distribution of charge does not lead to an overall dipole moment

normality—concentration of a solution defined as the molar concentration divided by an equivalence factor (i.e., H₂SO₄ can neutralize two equivalents of base with its two H⁺ groups, so a 1 M solution of H₂SO₄ is 2 N; the equivalence factor of H₂SO₄ is 0.5)

nucleation—a process through which a crystal, or a drop of liquid, grows around a small site

nucleic acid—general term for RNA and DNA, composed of a nucleotides, which are in turn each composed of a sugar, a phosphate group, and a nucleobase

nucleobase—nitrogen-containing molecules that form nucleic acids; adenine, cystosine, guanine, thymine, uracil are the major nucleobases; form base pairs via hydrogen bonding between the two helical strands of DNA

nucleophile—a molecule that donates an electron pair (i.e., a Lewis base) to an electrophile (i.e., a Lewis acid), forming a bond

nucleoside—a biochemical molecule consisting of a nucleobase and a sugar molecule

nucleotide—a biochemical molecule consisting of a nucleobase, a sugar molecule, and one phosphate group

nucleus—the center of an atom, consisting of positively charged protons and neutral neutrons

octet rule—a rule for chemical bonding that says atoms “prefer” to have eight electrons in their valence shell

ohm—, the SI unit used to describe electrical resistance

ohmmeter—a device used to measure electrical resistance

olefin—a molecule containing a carbon-carbon double bond, also referred to as an alkene

orbital—a possible arrangement for the density of an electron around the nucleus

ortho—term used to describe two substituents on an aromatic ring that are bonded to adjacent positions

osmometry—the process/study of measuring the osmotic strength of a solution

osmosis—the diffusive process of solutes moving from areas of higher concentration to lower concentration

oxidant—an oxidizing agent, or a species that removes electrons from another species

oxidation state—indicates the extent of oxidation for an atom; synonymous with oxidation number

p orbital—an atomic orbital with an angular momentum quantum number of 1, shaped like a peanut

para—term used to describe two substituents on an aromatic ring that are bonded to positions opposite to each other

paramagnetic—a molecule with no net spin; a material that is only attracted in the presence of an external magnetic field

peptide—a polymer of amino acids

pH—a measure of the hydrogen ion concentration of a solution

phase—a state of matter (e.g., solid, liquid, or gas)

phase boundary—the interface between two phases (e.g., solid-liquid, liquid-gas, or solid-gas boundary)

phase diagram—a plot that shows the phase in which a material is expected to exist as a function of variables like temperature and pressure

photon—a quantum (or particle) of electromagnetic radiation

physical change—a change in the macroscopic properties of a substance without a change in its chemical composition

pi bond—a chemical bond in which two lobes of two orbitals on adjacent atoms overlap favorably

pKa—the logarithm of an acid dissociation constant

plasma—a phase of matter in which a significant fraction of electrons have been ionized from their nuclei

polar—a compound in which the charge distribution leads to an overall dipole moment

polydentate—a ligand is described as polydentate if it can bind to a central atom multiple times

polymer—a “chain molecule” consisting of a repeating series of a single unit, or possibly multiple repeating units

polymorph—one of the crystalline forms of a substance that can crystallize in multiple forms

potential energy—the energy contained within an object as a result of its current state (its charge distribution, its position relative to other objects, etc.)

precipitation—the process through which a substance comes out of solution, usually due to insolubility

precision—the extent to which a measurement is repeatable (note that this is distinct from accuracy)

product—substance produced by a chemical reaction

proton—a charged subatomic particle found in the nucleus of an atom with a charge equal

and opposite to that of an electron

pyrophoric—a substance that tends to ignite readily and spontaneously upon exposure to air

qualitative analysis—analysis of the identity of the constituent species present in a sample

quantitative analysis—analysis of the specific amounts of the constituent species present in a sample

quantum—a discrete amount of energy, electric charge, or another physical quantity

quantum mechanics—the branch of physics that describes the motion and interactions of subatomic particles

quantum number—values of conserved quantities in a quantum mechanical system; electrons are described using four quantum numbers: n, the principal quantum number; l, the azimuthal quantum number; ml, the magnetic quantum number; and, ms, the spin quantum number

racemic—a mixture of equal amounts of the two enantiomers of a chiral molecule

radiation—the emission of energy as an electromagnetic wave

radical—a species containing unpaired electron density, typically involving an odd number of valence electrons

radioactive—emission of radiation or particles

Raoult’s Law—states that the vapor pressure of a solution depends on the amount (mole fraction) of a solute added to it

rare earth element—term for the lanthanides and actinides (including scandium and yttrium)

rate constant—a numerical value that characterizes the rate at which a chemical reaction takes place

rate determining step—the slowest step in a multiple step chemical process; usually the step with the highest energy transition state

reactant—a compound that is consumed or transformed by a chemical reaction

reaction—the process of changing chemical bonds in a molecular or ionic compound

reaction order—the number of chemical species simultaneously involved in a chemical reaction

reaction rate—how fast the reaction takes place, typically measured in terms of a change in concentration of a chemical species with respect to time

reductant—a reducing agent, or a species that gives electrons to another species

resonance—a way of describing the delocalization of electron density in a molecule

reversible reaction—a reaction where the products can be converted back into the reactants

RNA—ribonucleic acid; composed of a chain of nucleotides; encodes genetic information

s orbital—an atomic orbital with an angular momentum quantum number of 0, shaped like a sphere

salt—an ionic compound that can be thought of to form from the neutralization of an acid or base

salt bridge—a method used to place the two sides (solutions) of an electrochemical cell in electrical contact

saponification—technically the hydrolysis of triglycerides (i.e., triesters) with sodium hydroxide; more generally refers to hydrolysis of any ester

saturated compound—a molecule with no pi bonds or ring structures

saturated solution—a solution that contains the maximum amount of dissolvable solution (i.e., the addition of any more solution will not dissolve, and will remain in a separate phase)

scientific notation—a way of expressing a number a the product of a decimal and a power of 10 (for example, 1,050 = 1.05 × 103)

semi-metal—an element, compound, or alloy that has metallic and nonmetallic properties; also known as “metalloid”

shell—a way of classifying the orbitals in which electrons can reside based on their principle quantum number

sigma bond—a chemical bond involving direct overlap between orbitals on adjacent atoms, sigma bonds are symmetric with respect to rotation around the bond axis

significant figure—a digit in a number that is known with some amount of accuracy

soluble—a property describing a species that can be dissolved in a particular solvent

solute—a substance that is dissolved in a solution, present in a much smaller quantity than the solvent itself

solution—a liquid mixture containing multiple components, typically with one major component and one or more minor components

solvent—the major component of a solution

sorption—attachment of one substance to another; see absorption and adsorption

specific gravity—the ratio of a compounds density to the density of a reference material (usually water for liquids)

specific heat—the quantity of heat energy needed to increase the temperature of a substance by a fixed amount

specific volume—the volume occupied by a compound per unit mass

spectrum—a plot of the absorption intensity of light by a sample as a function of wavelength

spin—a type of angular momentum possessed by electrons and some other particles

stereochemistry—relative arrangement of atoms of a molecule in 3D space (see also stereoisomer, enantiomer, diastereomer)

stereoisomer—molecules that differ only in the spatial arrangement of their atoms

stoichiometry—the ratio of quantities in which reactants are consumed and products are formed in a chemical reaction

sublimation—phase transition from solid to gas without passing through the liquid phase (e.g., the “smoke” that dry ice gives off)

substituent—an atom or group of atoms occupying a designated position in a molecule

substitution reaction—a chemical reaction that replaces one substituent with another

substrate—a molecule that reacts with a reagent; a subjective label as the substrate is also a reagent

sugar—a carbohydrate (a molecule composed of only carbon, hydrogen, and oxygen) that tastes sweet; monosaccharides (or simple sugars) include fructose, galactose, and glucose

surfactant—a solute that reduces the surface tension of a liquid

syndiotactic polymer—a polymer in which substituents are located on alternating sides of the backbone

tautomer—structural isomers that differ only in the position hydrogen atoms

temperature—a physical property of matter that describes the average kinetic energy of molecules

thermoplastic—a type of plastic that hardens when heated and then cooled

titration—the process of measuring the concentration of an analyte by reacting a second solution of known concentration to cause a reaction

transition metal—typically, this refers to any element in the d-block (groups 3 through 12) of the periodic table

triple point—the combination of temperature and pressure values at which solid, liquid, and gas phases of a substance are in equilibrium

ultraviolet—electromagnetic radiation with wavelengths of 10 nm to 400 mm, just shorter than the visible spectrum, but not as short as X-rays

unimolecular reaction—a reaction that takes place involving only a single reactant molecule (there can be one or more product molecules formed)

unit cell—the smallest group of atoms, in a crystal, required to represent the symmetry and overall three-dimensional structure of the crystal

unsaturated compound—a molecule with at least one pi bond or ring structure

valence band—highest energy range in which electrons are normally present at 0 K

valence electron—an electron in the valence shell of an atom

valence shell—the highest partially occupied shell of electrons in an atom

van der Walls force—intermolecular forces between molecules resulting from the interactions of dipoles or induced dipoles

van der Walls radius—the radius of an imaginary sphere that can be used to represent the effective size of an atom

vapor pressure—partial pressure in the gas phase of a substance in equilibrium with its solid or liquid phase

viscosity—a property describing the consistency of a fluid by its ability to be deformed by stress, this is related to its ability to flow

volatile—a substance that easily evaporates at normal temperatures and pressures

voltage—the difference in electrical potential between two locations

voltmeter—a device used to measure an amount of electricity

volume—the quantity of space that a substance occupies

vulcanization—chemical reaction that creates crosslinks between individual polymer chains in rubber

wavenumber—inverse of wavelength, typically reported in units of m⁻¹ or cm⁻¹

weight—the force applied by gravity on an object

work—a force acting over a distance, such as a person lifting a box

X-ray—a form of short wavelength electromagnetic radiation