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Chemistry Dictionary

Chemistry definitions.  Some definitions contain a link to a page with a more complete explanation.

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Absolute Zero 0 K or -273.15°C.  This is the temperature at which molecular motion is at a minimum.
Accuracy How close a particular measurement is to the true value.
Acid A chemical that can act as a proton donor (Bronsted-Lowry theory) or is an electron acceptor (Lewis theory)
Acid Ionization Constant (Ka) Equilibrium constant for a Bronsted-Lowry acid given by the formula Ka = [H]*[A] / [HA]
Actinide Element in the 2nd row of the f-block elements.
Activation Energy (Ea) The amount of energy that must be put into a reaction for it to proceed.
Active Site The specific area in an enzyme where the enzyme can perform a catalytic function.
Activity Series An ordered list of chemicals based on how easily they can be oxidized.
Actual Yield How much product was actually made in a reaction - determined by measurement.
Adduct Generic name for a compound formed by the combination of a Lewis acid and a Lewis base.
Alcohol Any organic compound that contains a -OH functional group.
Aldehyde Any organic compound that contains a carbonyl (C=O) attached to a H.  -CHO
Alkali Metal Any element from the first column of the periodic table (group 1)
Alkaline Earth Metal Any element from the second column of the periodic table (group 2)
Alkane A single bond between carbon atoms, with each carbon bonded to three other atoms.  Given by the general formula CnH(2n+2)
Alkene A double bond between carbon atoms, with each carbon bonded to two other atoms. 
Alkyne A triple bond between carbon atoms, with each carbon bonded to one other atom.
Alloy Mixture of 2 or more metals
Amalgam A solution of a metal in mercury (Hg)
Amide Any organic compound that contains a carbonyl (C=O) attached to a -NH- group.
Amine A chemical that looks like ammonia (NH3) but where any or all of the N-H bonds can be replaced with a N-C bond.
Amino Acid A chemical that contains both a carboxylic acid (-CO2H) and an amine (-NH2)
Ampere Most common unit to measure electric current.
Amphiprotic A chemical that can act as both a proton donor and a proton acceptor.
Amplitude The height of a wave.  See "peak-to-peak amplitude" and "peak amplitude".
Anion Any chemical ion that contains a negative charge (ex. I-)
Anode In an electrical system, the electrode where oxidation occurs.
Antibonding Orbital An orbital involved in molecular orbital (MO) bonding theory which is less stable (higher energy) than the atomic orbitals from which it was formed.
Aqueous Any solution that uses water as the solvent.
Arrhenius Equation Equation used in kinetics that describes how rate constants depend on temperature and activation energy.  k = Ae-Ea/RT
Atmosphere (atm) A common unit of pressure that is based on normal pressure at sea level where pressure = 1atm. 
Atom The most basic unit of chemical matter containing both a nucleus of protons and neutrons, and electrons.
Atomic Number (Z) The number of protons in an atom's nucleus.
Atomic Orbital Describes the areas of electron density around an atoms nucleus
Atomic Radius The distance from the center of an atoms nucleus to the farthest electron(s) of that atom.
Atomic Symbol The letters assigned to a particular element (ex. chlorine = Cl)
Atomic Theory The theory that all matter is composed of atoms, which can not change their basic properties (ex. lead can not be turned into gold)
Aufbau Principle The most stable form of an atom comes from placing electrons in the lowest energy, available, atomic orbital.
Avogadro's Constant The number of atoms contained in 1 mole.  6.022142 x 1023 particles/mole
Azimuthal Quantum Number (l) Describes the shape of an atomic orbital and can range from 0 to n-1.

 

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Band Gap Energy difference between the highest energy, filled orbital, and the lowest energy, empty orbital.
Barometer Any instrument that measures atmospheric pressure.
Base A chemical that can act as a proton acceptor (Bronsted-Lowry theory) or is an electron donor (Lewis theory)
Base Ionization Constant (Kb) Equilibrium constant for a Bronsted-Lowry base given by the formula Kb = [BH]*[OH] / [B]
Bent shape The shape of a molecule with 3 atoms that have a bond angle less than 180°.
Binary Compound Any chemical that is made up of only 2 different elements.
Body Centered Cubic (BCC) A type of crystal structure where the unit cell is a cube with the same element in the middle and on all 4 corners.
Boiling Point The temperature at which a liquid will boil.  At this point, the vapor pressure of the liquid is equal to the atmospheric pressure.
Boltzmann Distribution The way that molecular kinetic energies are distributed among a collection of molecules.
Bond A strong attractive force between two molecules created by the sharing of electrons.
Bond Angle The angle between two atoms that are bonded to a common 3rd atom.
Bond Energy Amount of energy that is required to break a chemical bond.
Bond Length Average distance between two atoms bonded together.
Bond Order The # of pairs of electrons involved in a chemical bond.
Bonding Orbital An orbital involved in molecular orbital (MO) bonding theory which is more stable (lower energy) than the atomic orbitals from which it was formed.
Bronsted-Lowry An acid/base theory in which protons (H+) are transferred between molecules.  Acids are proton donors and bases are proton acceptors.
Buffer Capacity The amount of acid or base that can be added to a buffered solution before additions cause a large change in pH.
Buffer Equation More commonly known as the Henderson-Hasselbalch equation which relates pKa, pH, and the concentration of the weak acid - weak base pair.
Buffer Solution A solution of a weak acid and its conjugate base that resists pH changes when another acid or base is added to the solution.
Buret Tall piece of glass tube used to accurately measure volume.  Used commonly in titrations.

 

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Calorimeter Any device that can be used to measure the amount of heat emitted or absorbed over any length of time.
Capillary Action Liquid moving against gravity in a narrow tube.
Carbohydrate A common chemical in biology given by the formula (CH2O)n
Carbonyl Any carbon double-bonded to an oxygen (C=O)
Carboxylic Acid Any acid that has a -CO2H functional group.
Catalyst Anything that speeds up the rate of a chemical reaction but is not being produced or consumed in the reaction.
Cathode In an electrical system, the electrode where reduction occurs.
Cation Any chemical ion that contains a positive charge         (ex. Cu2+)
Cell Potential The difference in electric potential (E) between a cells anode and cathode.  Measured in volts.
Celsius Degrees (°C) Temperature scale used by most of the world, where 0°C is the freezing point of pure water, and 100°C is the boiling point of pure water.
Chelate A complex formed by polydentate ligands (ligands that can bind in more than one place)
Chelate Effect The effect of a complex becoming more stable when bound with polydentate ligands.
Chemical Energy Energy that is stored in chemical bonds.
Chemical Equation Way to write a chemical reaction that describes both reactants and products as well as gives relative amounts of each.
Chemical Equilibrium The point of a reversible chemical reaction where no net change can be seen because the reaction is proceeding both forwards and backwards at the same rate.
Chemical Kinetics An area of chemistry that studies how fast reactions occur
Chemical Nomenclature A systematic way in which chemicals are given names.
Chemistry The study of the elements and how they interact.
Chromatography A way of separating substances based on their characteristics usually using a liquid mobile phase and a solid stationary phase.
Close Packed The way in which atoms are packed in a crystal to take up the least amount of physical space.
Closed System A system that can absorb or emit energy to its surroundings, but can not transfer matter.
Cohesive Force A force that pushes similar chemicals in the same phase together.
Colligative Property Any property of a solution that depends on the concentration of the solution.
Combustion The reaction that occurs between a substance and oxygen that releases energy.
Common Ion Effect The effect of reduced solubility caused by the presence of one of the ions involved.  See LeChatliers Principle
Common Name A name used in place of a more technical name for a chemical.  (ex, NaCl is referred to as table salt)
Complex Ion A substance formed from the bonding of a metal ion to a chemical containing lone pairs.
Compound Any chemical made of 2 or more separate elements bonded together.
Concentration The amount of a solute that is dissolved in a solvent.
Condensation Reaction A reaction in which 2 molecules are bonded together and water is created as a byproduct.
Conduction Band A "band" of molecular orbitals where electrons can travel freely.
Conductor Any substance that conducts electricity well.
Conjugate Acid-Base Pair Bronsted-Lowry acid such as CH3COOH (acetic acid) that loses its proton (H+) to form a base CH3COO- (acetate).
Conserved A substance's amount does not change.
Conversion Ratio A ratio used to convert from one unit to another one.   (ex. 1 inch = 2.54 centimeters)
Coordination Complex A cation (usually a metal) that binds covalently to 2 or more other substances (ligands).
Coordination Number The number of atoms that are bonded to the central atom.
Copolymerization Using two or more monomers to form a single polymer.
Core Electrons Electrons not in the Valence (outermost) shell of an atom.
Corrosion When a metal is oxidized in any environment.
Coulomb's Law Describes the interaction of two electrically charged objects.  Fel = k (q1*q2)/r2
Coupled Reaction A pair of reactions in which one of the reactions drives the other
Covalent Bond A bond in which electrons are shared equally between atoms.
Critical Mass The smallest amount of nuclear material that is needed to create a self-sustaining fission reaction.
Crosslinking When separate chains of a polymer form bonds between them.
Crystal Field Splitting Energy The energy difference between the 5 d orbitals when they are split into groups of 3 and 2.
Crystal Field Theory A theory that describes how the d orbitals of a transition metal complex split into 2 energy levels based on the electronic properties of the ligands attached.
Cyclotron A particle accelerator that is used to make really high energy nuclear particles by bouncing them off each other at high speeds.

 

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Dalton's Law of Partial Pressures States that each gas in a mixture contributes the same pressure as it would by itself.
Degenerate Orbitals Molecular Orbitals that have the same energy.
Delocalized Not localized.  Spread out over space.
Delocalized Orbital Any molecular orbital in which the orbital is spread over 2 or more atoms.
Density Mass / Volume
Desorption When an adsorbed molecule is detached.
Deuterium (D) 2H - An isotope of hydrogen containing 1 proton and 1 neutron.
Diamagnetic A substance that is repelled by a magnetic field as a result of having no unpaired electrons.
Diatomic Molecule Any molecule that has exactly 2 atoms.
Diffusion The mixing of solutions caused by molecular motion over time.
Dilution Creating a less concentrated solution by adding more solvent.
Dipolar Force Attractive force between two polar chemicals.  The positive side of one is attracted to the negative side of the other.
Dipole Moment The electrical properties of a compound resulting from an uneven charge distribution.
Diprotic Acid Bronsted-Lowry acid that can donate 2 protons (H)
Dispersion Force Attractive force between molecules that have temporary dipole moments.
Dominant Equilibrium The most important equilibrium in determining concentrations when more than one equilibrium is involved.
Donor Atom Any atom that can contribute electrons to a covalent bond.
Doped Semiconductor A metal to which "impurities" have been added, usually to increase conductivity.
Double Bond A bond between atoms that involves 2 pairs of electrons, or 4 electrons total.
Ductile Something that can be drawn into tubes or wires.
Dynamic Continually changing.  Molecules in constant motion.
Dynamic Equilibrium The point of a reversible chemical reaction where no net change can be seen because the reaction is proceeding both forwards and backwards at the same rate.

 

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Effective Collision When molecules collide and a reaction takes place.
Effective Nuclear Charge The total positive charge felt by an electron.  Equals the nuclear charge minus any effects of "screening" electrons.
Elastomer A polymer that is flexible.
Electrical Force Force felt between two charged objects.
Electrochemical Reaction A redox reaction that forces a charge through an external electrical circuit.
Electrode A conductor that connects an electrochemical reaction with an external circuit.
Electrolysis A non-spontaneous chemical reaction that is driven by electricity.
Electrolytic Cell A cell where electrolysis can occur.
Electromagnetic Radiation Waves that have both electrical and magnetic properties.
Electron Particle that surrounds atoms and has a negative electrical charge of -1.602x10-19C and a mass of 9.11x10-31kg
Electron Affinity The amount of energy related to the coupling of an electron to an atom.
Electron Capture A type of nuclear decay in which a core electron is captured by an unstable nucleus, converting a proton into a neutron.
Electron Configuration How a particular atoms or molecules electrons are distributed amongst its orbitals.
Electron Deficient An atom that does not have enough electrons to fill the valence shell.
Electron Density A mathematical prediction of the probability of the location of an electron around an atom.
Electronegativity Both a relative and quantitative scale which describes how strongly an atom will attract electrons involved in bonding.
Electroplating When something is coated in a metal using electrolysis.  New copper pennies are mostly Zinc, coated with Copper.
Element A particular substance in which all the atoms have the same number of protons.
Elemental Analysis Analysis to find which elements, and their percent by mass, a compound contains.
Emission Spectrum The different wavelengths of light (photons) that are emitted by the relaxation of an electron from an excited state.
Empirical Formula The chemical formula of a compound written with the smallest possible integers.  (ex. H4O2 is a chemical formula for water, H2O is the empirical formula)
Endothermic Something that absorbs some form of energy.
Energy Theoretical term that describes how much work can be done.
Energy Level The amount of energy that a particular species has.
Enthalpy (H) Also known as the heat content, describes the thermodynamic potential of a system in terms of energy.  H = E + P*V
Entropy (S) A measurement of disorder in thermodynamics.
Enzyme Natures catalysts.
Equatorial Position In a trigonal bipyramidal compound, a space that exists in the trigonal plane.
Equilibrium When a system shows no net change over time.
Equilibrium Constant (K) Similar to Ka and Kb, a value that determines the concentrations of products and reactants of a particular reaction.  Given by the general formula K=[A]a[B]b/[C]c[D]d
Ester Any compound that has a carbonyl bonded to an O that is bonded to something else.     -(C=O)-O-
Ether Any compound that has a C-O-C bond.
Evaporation When a compound goes from a liquid to a gaseous state.
Excited State When an electron is in an orbital that has more energy than another, empty orbital.
Exothermic Something that emits some form of energy.
Extensive Property A property that depends on the size of the sample.  (ex. length, mass)

 

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Faraday's Constant (F) Electrical charge in 1 mol of electrons equal to 9.64834x104 C/mol
First Law of Thermodynamics Energy is always conserved.  It can not be created or destroyed.  ΔE= q + w
First-Order Reaction A reaction that is dependent on concentration taken to the first power.
Fission A type of nuclear reaction where a nucleus breaks up into two smaller ones.
Formal Charge The charge of a particular atom in a compound based on the elements column in the periodic table, and the number of valence electrons surrounding the atom.
Formation Constant An equilibrium constant for the formation of a new compound.
Formation Reaction