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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. (see also, paramagnetic)
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 A reaction in which a compound is formed from each element in its standard state.
Free Energy (G) Thermodynamic free energy determined by enthalpy and entropy.  G = H - T*S or         ΔG = ΔH - TΔS
Free Radical A chemical that is extremely reactive because it contains an unpaired, lone electron.
Free Radical Polymerization Polymerization that occurs as a result of reaction mechanisms that involve free radicals.
Freezing Point The temperature for a particular compound where the liquid freezes to form a solid.
Freezing Point Depression When a freezing point is lower due to the effects of impurities in the solution.
Frequency (ν) The number of waves that occur at a point over a given time.
Functional Group A particular atom or group of atoms in a molecule that give the molecule certain properties.  (ex. carbonyl, alcohol, aldehyde)
Fusion A type of nuclear reaction where two nuclei come together to form one large nucleus.



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Galvanic Cell A reaction system in which an electrochemical reaction occurs spontaneously to force voltage through an external circuit.
Gamma Ray (γ) High-energy photon (<10pm wavelength) that is emitted by nuclear decay. 
Gas A substance whose intermolecular forces are weak enough to allow expansion and contraction to fill a given volume.
Gas Constant (R) Constant used to link temperature to energy or pressure per mol.  R = 8.314 J / mol K  or  R = 0.08206 L atm / mol K
Geometric Isomers Two chemicals that have all the same elements, but the elements are not all in the same places.
Globular Protein A protein whose tertiary structure is compact and spherical.
Gravitation Force The force between two objects caused by their mass.
Greenhouse Effect The heating of the earth caused by atmospheric gases absorbing infrared radiation.
Ground State When the lowest energy, most stable, electron orbitals are full.
Group A particular column of the periodic table.



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Haber Process An industrial process that creates ammonia from hydrogen and nitrogen.
Half-Life (t1/2) A set amount of time in which half of a reactant will be consumed in the reaction.  t1/2 = ln(2) / k
Half-Reaction Usually referring to either an oxidation or reduction reaction as a part of a redox reaction that shows the electrons.
Halogen Any element in the second to last column (group 17) of the periodic table.
Hard Acid Lewis Acid that is not easily polarized.
Hard Base Lewis Base that is not easily polarized.  It's donor electrons are tightly bound.
Heat (q) The transfer of energy in thermodynamics from a system to its surroundings or vice versa.
Heat Capacity Constant for a particular compound expressed in J / mol K.  The amount of energy required to raise the temperature of 1 mol by 1°C or 1K
Heat of Dilution The change in enthalpy related to the dilution of a solution.
Heat of Solution The change in enthalpy related to the dissolving of a solute in a solvent.
Heat of Vaporization The change in enthalpy related to the vaporization of a liquid.
Henry's Law States that the partial pressure of a gas in the atmosphere above a solution is directly related to the concentration of that gas in the solution.
Henry's Law Constant Constant that describes how the partial pressure of a gas above a solution and the concentration of that gas in solution are related.
Hess' Law The net change in enthalpy to get from A to B is equal to the sum of the enthalpy of the steps to get from A to B.
Heterogeneous Something that contains more than one component and is not uniform in its composition.
High-Spin Complex In crystal field theory, a compound whose d orbitals have a low splitting energy, causing electrons to fill the (slightly) higher energy orbitals before flipping spins and pairing with the electrons already in the lower energy d orbitals.
Homogeneous Something that contains only one component and has a uniform distribution.
Hund's Rule In degenerate orbitals, electrons will fill in all empty orbitals before flipping and pairing with another electron.  This is the most stable conformation.
Hybrid Orbital An atomic orbital created by the combination of two or more other orbitals.
Hybridization The creation of a hybrid orbital by combining two or more atomic orbitals.
Hydrate A chemical compound that has water molecules included in its structure.
Hydrocarbon Any compound containing only hydrogen and carbon.
Hydrogen Bond Intermolecular force in which a H atom weakly bonds with a highly electronegative atom such as F, O or N.
Hydrophilic Water loving. 
Hydrophobic Water hating.
Hydroxyl Group -OH functional group.



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Ideal Gas Hypothetical gas that is assumed to have no intermolecular forces or molecular volume whose behavior can be described by PV=nRT
Indicator A chemical used to indicate the endpoint of a titration because of its color change at a certain pH.
Induced Fit When an enzyme and the chemical binding to it change their shapes to fit together better.
Induced Nuclear Reaction A nuclear reaction caused by a nuclear projectile colliding with an atomic nucleus.
Ineffective Collision Any collision between molecules that does not lead to a reaction.
Initial Concentration The concentration at the beginning of a reaction, before the reaction actually happens.
Initiation Ceremony marking membership in an organization.  Ok, I'm kidding - it's a chemical reaction that starts polymerization.
Initiator The substance that causes initiation.
Inner Atom Any atom that is on the "inside" of a molecule by being bound to more than 1 other atom.
Insoluble A chemical that can not be dissolved into a solution.  (Ksp<<1)
Integrated Rate Law Gives the concentration of a substance based on time.
Intensity How bright a light is.  Related to the number of photons.
Intensive Property A property that does not depend on the size of the sample.  (ex. temperature, density)
Intermediate A chemical that is formed as a result of how a reaction occurs.  Are usually produced and consumed very quickly en route to the final product.
Intermolecular Force Any force between molecules such as hydrogen bonding or dispersion forces.
International System of Units (SI) Metric Scale.  Internationally agreed upon standard measurements.
Intramolecular Force Any force between atoms in one molecule.
Ion An element that has a charge.
Ionic Compound A compound that is neutral overall but is made up of both cations and anions.
Ionic Solid A solid ionic compound whose molecules are attracted to each other by coulombic interactions rather than covalent bonds.
Ionization Energy The amount of energy that is needed to remove an electron from a molecule.
Isoelectronic Have the same number of electrons
Isomers Any molecules that have the same number and type of atoms, but have different structures.
Isotope Same atom, different number of neutrons.



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Joule (J) Standard (SI) energy unit.  1 J = 1kg*m2/s2



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Kelvin Standard temperature unit based on the Celsius scale where °C = K + 273.15 and 0 K is absolute zero.
Ketone Any compound that has a carbonyl group (C=O) attached to two carbons.
Kilogram (kg) Standard (SI) unit for mass.
Kinetic Energy The energy contained in the motion of something.  Ekinetic = 1/2 m*u2.
Kinetics The study of how fast a chemical reaction occurs.



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Lanthanide Any element in the 4f block of the periodic table from (57) La to (70) Yb
Lattice A number of atoms organized into a regular and repeating pattern in a 3-dimensional structure
Lattice Energy The amount of energy released when atoms in the gaseous state condense into a lattice.
Law of Conservation of Energy Law that says that energy can not be created or destroyed.  True except for nuclear reactions where mass is converted into energy, thus "creating energy" as governed by Einstein's famous E=MC2
Law of Conservation of Mass Law that says that mass can not be created or destroyed.  True except for nuclear reactions where mass is converted into energy, thus "creating energy" as governed by Einstein's famous E=MC2
Lead Battery Battery commonly used in cars.  A basic voltaic cell in which both half reactions involve lead
Le Chatlier's Principle If a reaction is at equilibrium, and one of the elements of the reaction is added, then the reaction will proceed in a direction to maintain equilibrium. (If you add something on the right of the reaction, it will react backwards and increase the elements on the left of the reaction)
Length A distance measuring how much space an object occupies
Lewis Acid An electron-pair acceptor in the Lewis Acid/Base theory
Lewis Base An electron-pair donor in the Lewis Acid/Base theory
Lewis Structure A way of representing the structure of a molecule using element symbols, lines to represent bonds, and dots to represent non-bonding electrons.
Ligand Something that acts as a lewis base, donating a pair of electrons to a metal atom or a cation in order to form a bond.
Light Photons.  Visible light is photons with a wavelength between 400 and 700 nanometers.
Limiting Reactant In a reaction, the element that runs out first, stopping the reaction from proceeding any further.
Linear Straight line
Linear (electronic/molecular) Geometry State of an atom in a molecule in which any bonded atoms are located on a straight line.
Linear Accelerator Device used to accelerate particles (like atomic nuclei) along a straight line
Line Structure Simplified lewis structures for carbon containing molecules in which C atoms are implied at the "joints", in addition, H atoms are implied without having to draw.
Liquid One of the phases of matter in which the volume of a substance remains the same, but the shape of the substance can change constantly.  Water is a liquid.  Duh.
Liter (L) Standard unit of volume in the metric system equal to 1000cm3
Lone Pair A pair of electrons on an atom that is not involved in any bond.
Low-Spin Complex Based on Crystal Field Theory - a complex in which electrons are paired in the lower of the split d orbitals before they are added to the higher of the split d orbitals



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Macromolecule A really big molecule.  Usually more than a couple hundred atoms.
Macroscopic Something that you can see without the help of a magnifying device like a microscope.
Magnet Something that has no net electric charge, but can either attract or repel a moving electrical charge.
Magnetic Force The force of either attraction or repulsion between two or more objects
Magnetic Quantum Number (ml) A quantum number valued from + l to - l and all the integers in between (if l = 2, ml can be   -2,-1,0,1,2)  Tells you where in space an atomic orbital is.
Magnitude How large or small a number is.
Main Group Element An element in the p block of the periodic table
Main Group Metal An element in the p block of the periodic table that displays metallic properties
Major Species In an aqueous solution, the element (molecules, anions, cations) that is most prevalent
Malleable Something that be shaped in its solid form.
Manometer A simple instrument used to measure pressure in which a u-shaped tube is filled with a liquid and each end is exposed to different pressures
Mass The amount of matter in an object.  Different from weight.
Mass Number (A) In an atoms nucleus, the total number of protons and neutrons (protons + neutrons =A)
Mass Percent Composition How much of a particular element is in an element expressed as a percent of total mass.  To find, divide the total mass of an element(s) by the total mass of the molecule 
Matter Anything that has a mass and occupies space
Mechanism The specific way in which a chemical reaction occurs.  Usually shown in steps using arrows and half arrows to denote movement of electrons
Meniscus The curved portion of a liquid in a small tube
Mesosphere The part of the earths atmosphere located from 50km and 85km above the surface of the earth
Metabolism The breakdown of molecules in a biochemical cell
Metal Any element that tends to lose electrons to form cations and conducts both heat and electricity well
Metalloid An element that is a semi-metal.  That is, it displays properties between those of a metal and a non-metal
Metallurgy A science of working with metals to extract, purify, and create useful substances with them
Metathesis Reaction Also known as a double displacement reaction.  Two molecules exchange bonded atoms.  (AB + CD -> AD + CB)
Meter (m) Standard unit of length
Micelle A large group of molecules in where each molecule has a hydrophobic end pointing in, and a a hydrophilic end pointing out
Microscopic Something that needs a magnifying device to see
Midpoint The point in a titration reaction where 1/2 of the amount of titrant needed to reach the end point has been added
Minor Species In an aqueous solution, the element (molecules, anions, cations) that is not the most prevalent
Miscible Something that is soluble, in any amount
Mixture Something that has 2 or more substances
Moderator Useless person in presidential debates that is supposed to keep "order".  OR a substance that is used to slow down neutrons in a nuclear reactor (or any chemical reaction)
Molar Heat of Solution The amount of energy released or taken in when a substance is dissolved in solution
Molar Mass The mass (in g) of one mole of a substance
Molarity The number of moles of a substance in 1L of solution
Mole 6.022x1023 atoms.  Comes from the number of atoms of Carbon to weigh 12g
Mole Fraction A ratio of the number of moles of 1 element to the total number of moles of all elements.  Ex, In H2O, the mole fraction of O is 1:3 (1 mole of O, 3 moles of all elements)
Molecular Density Just like regular density, but for molecules.  The number of molecules contained in a specific volume
Molecular Geometry The shape of a molecule that is derived from how the different atoms are situated in space.
Molecular View Imagine being the size of a molecule.  Molecular view is just how things would look from a molecules perspective
Molecule A group of atoms that are connected by chemical bonds
Monodentate Any ligand that contains only 1 donor atom
Monomer Used in the production of polymers.  A single molecule that, in a polymer, repeats itself



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Near Degenerate Orbitals Molecular orbitals that have nearly identical energies.  Degenerate orbitals have exactly identical energies
Nernst Equation E=E0 - (RT/nF) lnQ

Used to relate the potential of an electrochemical cell (E) to standard potentials (E0) and concentrations (through Q)

Net Ionic Equation One way of writing a chemical reaction that shows which elements are participating in the reaction
Network Solid Solid held together by covalent bonds
Neutral Atom Any atom that has the same number of protons and electrons
Neutralization Reaction Any reaction in which a proton is transferred between an acid and a base to produce neutral molecules
Neutron Subatomic particle that has mass, but no electrical charge
Newton Standard unit of force
Nitrogen Fixation A conversion of pure nitrogen (molecules) into other molecules that contain nitrogen (ex, ammonia)
Noble Gas Any element in the right hand column (Group 18) on the periodic table
Node In molecular orbitals, a point where the electron density is 0
Nomenclature A specified set of rules used in order to name chemicals.
Nonbonding Electron Any electron that is located in the valence shell that does not participate in bonding
Nonmetal Any element that isn't a metal or metalloid.  Do not usually form cations
Normal Boiling Point The point at which a liquid transitions to a gas under normal pressure
N-type Semiconductor A metalloid that has been "doped" with another element in order to have an excess of valence electrons
Nuclear Binding Energy The amount of energy holding each subatomic particle in an atoms nucleus together
Nuclear Decay When an unstable nucleus spontaneously decomposes into other things
Nucleon A proton or neutron contained in an atoms nucleus
Nucleotide In DNA and RNA, a repeating unit that contains a base, a phosphate, and a 5 C sugar group
Nucleus The center of an atom containing protons and neutrons
Nuclide A specific nucleus given by its charge (Z) and mass (A)



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Octahedral A molecular geometry shape in which 6 atom are bonded to a single, center atom
Open System A system that is open to its surroundings, allowing exchange of heat, mass and energy
Orbital A three dimensional shape that describes where in space an electron is
Orbital Overlap When two separate orbitals overlap (occupy the same space) with each other
Order of Reaction Stems from rate laws - describes the exponent to which a concentration is raised
Organic Chemistry Branch of chemistry focused on Carbon (molecules and reactions)
Osmosis When a solvent moves through a semi-permeable membrane
Osmotic Pressure Pressure difference needed to prevent osmosis from occuring
Outer Atom An atom in a molecule that is "on the edge" and is only bonded to one other atom
Overall Order Add up all of the "Orders of Reactions" for each element in a reaction
Oxidation Loss of electrons (OIL - Oxidation Is Loss)
Oxidation Number The charge that an atom would have if all bonding electrons (bonded to more electronegative atoms) were removed
Oxidation-Reduction (Redox) Reactions A kind of reaction in which electrons are transferred, thereby oxidizing some atoms, and reducing others
Oxidization Agent The element that is being reduced (gains electrons) - causing something else to be oxidized
Oxyacid An acid containing -OH and O atoms
Oxyanion Any anion that is made up of a central atom bonded to atleast 2 Oxygen atoms
Ozone Layer Section of the earths atmosphere that contains Ozone (O3)



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Pairing Energy The repulsion between 2 electrons placed in the same orbital
Paramagnetic A substance that is attracted by a magnetic field as a result of having unpaired electrons. (see also, diamagnetic)
Partial Pressure In a system containing a mixture of gases, the pressure contributed from 1 particular gas
Parts per Billion (ppb) A unit of concentration telling us how many objects are in 1 billion objects (ug/kg)
Parts per Million (ppm) A unit of concentration telling us how many objects are in 1 million objects (ug/g)
Pascal (Pa) Unit of pressure - one Newton per m2
Passive Electrode An electrode in an electrochemical cell that does not participate in the redox reactions, and only transfers electrons
Pauli Exclusion Principle No 2 electrons can have the same wavefunction - or no 2 electrons can have the exact same set of quantum numbers
Peptide A small polymer made up of amino acids
Percent Yield How much product you actually got from a reaction.  (Actual/Theoretical x 100%)
Periodic Table Table that arranges the elements by increasing atomic number and similar properties
pH -log[H].  A measure of how acidic or basic a solution is
pH Meter An instrument that measures pH
Phase Solid, Liquid, or Gas
Phase Change Transition from one phase to another
Phase Diagram A graph showing what phase a chemical is in depending on Temperature and Pressure
Phospholipid A biochemical molecule that is an integral component of cell membranes
Photoelectric Effect A metal surface shooting off electrons when exposed to light.  Photons (light) of specific wavelengths correspond to certain energies that will release electrons
Photon A subatomic particle we understand as light.  Has an energy given by E=hv
Pi bond A bond formed by any orbitals that are side by side and perpendicular to the "bonding axis"
Physical Transformation When a chemicals physical properties are changed, but the chemical properties remain the same
Physical Property Any property that can be observed without changing the chemical properties
Pipet Lab device used to measure specific volumes of liquids
Planck's Constant (h) 6.63 x 10-34 J s.  A constant that relates the energy of a photon to its frequency (E=hv)
Plastic A polymer having a high molecular weight
Plastic (alternate) A substance that will undergo a permanent change of shape if it is strained beyond a certain point
Plasticizer Something added to a plastic in order to make it more flexible
Pleated Sheet or a Beta-Pleated Sheet - a secondary protein structure in which the amino acids form a flat, sheet like structure (as opposed to the twisting alpha-helix structure)
Polar Bond Any bond in which one atom either "gives" or "takes" an electron, instead of both atoms sharing that electron like in a covalent bond
Polarizability How easily the electron density around an atom can be distorted.
Polyamide Any polymer that links its monomers using an amide linkage group
Polyatomic A molecule that contains many atoms
Polyester Any polymer that links its monomers using an ester linkage group
Polymer A molecule that contains many individual units (monomers) linked together
Polypeptide A protein molecule composed of amino acids
Polyprotic Acid An acid that contains more than one H atom according to the Bronsted-Lowry Acid/Base theory
Positron The antimatter particle equivalent to an electron but having a positive charge
Positron Emission A kind of nuclear decay in which a positron is emitted, decreasing the atomic number, but leaving the mass number unchanged
Potential Energy How much energy something has that has not yet been realized in some way
Precipitate A solid that is formed in, and separates itself from a solution
Precipitation The formation of a precipitate
Precision How reproducible the results of an experiment are
Pressure The force of a substance over a certain area
Primary Structure The order in which amino acids are arranged in a protein
Principal Quantum Number (n) Number that tells you the energy and size of an atomic orbital.  The first row (H and He) have an n value of 1, the second row n=2, etc...
Product The substance that is made in a chemical reaction
Propagation When a polymerization reaction begins, propagation is the continuation of that reaction
Protein A polymer that is important in biochemistry and is made up of amino acids
Proton Subatomic particle contained in the nucleus of atoms that has a positive charge and mass
Proton Transfer When a H+ atom is transferred from one molecule to another
P-type Semiconductor A metalloid that has been "doped" with another element in order to have a deficiency of valence electrons



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Quantized Having real number values
Quantum Number A set of numbers that describe the state of an electron in an atom
Quantum Theory Theory of how subatomic particles interact



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Radiant Energy The amount of energy that photons have when emitted by electromagnetic radiation
Radiation Therapy Using radioactive substances to treat cancer
Radioactivity Energetic particles emitted as a nucleus undergoes spontaneous decay
Rate Amount of change over a given time
Rate Constant (k) A constant that tells you the rate of a reaction depending on the concentrations of the reagents
Rate Law A way of relating how fast a reaction proceeds (its rate) depending on the concentrations of the reagents
Rate-Determining Step In a reaction with more than one step, the step that occurs the slowest
Reactant A molecule that "reacts" (is consumed) during a chemical reaction
Reaction Quotient (Q) A ratio of the concentrations of products and reactants in a chemical reaction, with each raised to its stoichiometric coefficient.  In the reaction aA + bB -> cC + dD

Q= [C]c[D]d / [A]a[B]b

Redox Reaction (Oxidation-Reduction Reaction) A kind of reaction in which electrons are transferred, thereby oxidizing some atoms, and reducing others
Reducing Agent The element that is being oxidized (loses electrons) - causing something else to be reduced
Reduction Gain of electrons (RIG - Reduction Is Gain)
Resonance Some substances contain delocalized electrons, where more than one Lewis structure can be used to show where electrons are
Resonance Structure The various structures used to show resonance
Reversible Reaction A chemical reaction that can easily proceed in either direction
Reversibility A chemical reaction that has the ability to proceed in either direction
Ribonucleic Acid (RNA) Polymer of various nucleotides that transfers genetic information
Root-Mean-Square Take all the individual numbers and square them, then find the mean (average) of these numbers, and then take the root of the average
Rounding Increasing or decreasing the value of a number so that it only has a specific number of significant digits.  4.4999999 would round to 4, whereas 4.50101 would round to 5



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Saturated A solution that contains the absolute maximum that it can hold of a given substance
Schrodinger Equation Equation from quantum mechanics that describes the behavior of electrons in atoms
Scientific Notation A way of writing very large or very small numbers as a number between 1 and 10, multiplied by 10 to the appropriate power
Screening Electrons in the d-orbitals "screen" (block) some of the pull from the nucleus, reducing the effective nuclear charge
Second (s) Standard unit of time
Second Law of Thermodynamics Law that states that entropy (disorder) will always increase
Second-Generation Star A star formed from the collapse of a first generation star - elements will have a Z <27
Second-Order Reaction Any reaction whose overall order is equal to 2
Secondary Structure The way in which a string of amino acids forms - usually in ribbons or sheets
Seesaw Shape A molecular geometry shape that resembles a seesaw
Semiconductor Any substance that can somewhat conduct electricity.  Not as good a conductor as a pure metal, but not as bad a conductor as a non-metal
Semipermeable Membrane A thin membrane that allows certain things through (like a solvent) but not other things (like a solute)
SI (Systeme International) System of standard units used by scientists all over the world
Sigma Bond Any bond that is formed by orbitals on the "bonding axis" - directly between bonded atoms
Significant Figure A number that is known to be accurate up to the last digit it contains
Single Bond A chemical bond between two atoms created by sharing a pair of electrons.  Drawn as a single line
Slightly Soluble Something that is able to partially dissolve in a solution.  Ksp will be between 10-2 and 10-5
Soft Acid An acid according to the Lewis Acid/Base theory, whose electron accepting atom is highly polarizable
Soft Base A base according to the Lewis Acid/Base theory, whose electron donating atom is highly polarizable
Solid Phase of matter where the substance has a definite shape and volume
Solubility How much of a substance will dissolve in a solution
Solubility Product (Ksp) Equilibrium constant that tells how much of a substance will dissolve in a solution.
Soluble Something that can dissolve in a solution.  Ksp will be greater than 10-2
Solute Something that dissolves in a solvent to form a solution
Solution Any mixture of two or more substances, consisting of a solute and a solvent
Solvent Something in which other things can be dissolved.  The chemical present in the largest amount.
Space-Filling Model A computer generated molecular model that shows the space filled by the molecules electrons
Spectator Ions Any anions or cations that are present during a reaction, but do not actually participate in the reaction
Spectrochemical Series The order of ligands in crystal field theory according to the energy level difference between their split d-orbitals
Spectrum A graph of light according to either frequency or wavelength
Spin Orientation Quantum Number (ms) The quantum number that shows an electrons spin, either +1/2 or -1/2
Splitting Energy The difference in energy between d-orbitals when they split according to crystal field theory
Spontaneous Something that happens all by itself, without any outside stimuli
Square Planar A particular type of molecular geometry, stemming from the octahedral electron geometry, with two lone pairs of electrons.
Square Pyramid A particular type of molecular geometry, stemming from the octahedral electron geometry, with one long pair of electrons
Standard Conditions 1M solution, 1 atm pressure, and 298 K temperature
Standard Enthalpy of Formation The change in enthalpy that goes with the formation of a substance
Standard Hydrogen Electrode (SHE) Platinum wire in a 1M H+ (acid) solution in a 1atm H2(g) environment.  Serves as the standard reference value for standard reduction potentials, with a value defined to be 0 V
Standard Reduction Potential (E0) The potential for an electrode to be reduced under standard conditions
Standard Solution Any solution where the concentration is known very accurately
Standard State The phase in which a substance is in under standard conditions
Standardization A process to accurately find the concentration of a solution
Starch A carbohydrate that is used by plants to store energy
State Function Any property that depends only on the current state of a substance, not on what happened to the substance previously
Steric Number A number that describes the number of bonds + the number of lone pairs of electrons on an atom
Stoichiometric Coefficient The number that tells you the relative number of molecules that are participating in a chemical reaction.
Stoichiometric Point In a titration, its the point where the exact amount of titrant has been added to completely react with the chemical being titrated
Stoichiometry A way of describing the relative amounts of chemicals being used in a reaction
Stratosphere Section of the earths atmosphere that is between 10 and 50 km above the surface
Strong Acid An acid that almost completely dissociates from its H+ in water.
Strong Base A base that almost completely dissociates from its OH- in water
Structural Formula A way of writing a molecular formula that gives an indication of how the atoms are bonded together
Structural Isomers Any compounds that have the exact same molecular formula, but have different molecular structures
Sublimation When a solid changes directly into a gas.  Dry ice going to CO2(g) is a good example
Surface Tension Energy that holds liquids together, resisting a change to their surface area
Surfactant Any molecule that has both hydrophilic and hydrophobic parts and is used to change the behavior of an aqueous solution
Surroundings Anything that is outside a system
System A very specific area that is being studied



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Temperature A relative property of something that tells you how "hot" or "cold" something is.  Subatomically, it tells you the amount of random motion energy of a substance
Termination What happens when a polymerization reaction finishes
Termolecular Reaction A chemical reaction involving the collision of 3 separate molecules
Tertiary Structure The complete, overall structure of all of a protein
Tetrahedron A shape with 4 faces structured like a pyramid, where each face is an equilateral triangle
Theoretical Yield The amount of product that could theoretically be created if the reaction went to completion
Theory Something that puts together and explains a given set of facts
Thermal Energy Energy related to heat, the random motion of the atoms and molecules
Thermal Pollution Any industrial process that releases heat into the environment
Thermodynamics Area of chemistry devoted to the study of the various forms of energy, including heat
Thermosphere Area of the earths atmosphere located more than 90 km above the surface
Thiol An organic functional group containing a -SH
Third Law of Thermodynamics Law that states that a pure, crystalline substance at 0K will have an entropy of 0
Titrant In a titration, it is the liquid solution that is being added
Titration Analytical process in which a solution is slowly added to another solution in order to determine a concentration
Transition Metal Elements in the d block of the periodic table (group 3-12)
Trigonal Bipyramid A type of electron and molecular geometry with 7 areas of electron density surrounding a central atom.  The shape is of two trigonal pyramids, laid base to base
Trigonal Planar A type of electron and molecular geometry with 3 areas of electron density surrounding a central atom.  Forms a flat, triangle shape
Trigonal Pyramid A type of molecular geometry stemming from the tetrahedral electron geometry, whose shape is that of a 4-faced pyramid
Triple Bond A bond between atoms that involves the sharing of 3 lone pairs of electrons, drawn as three lines
Triple Point A specific temperature and pressure where all three phases of a substance can exist in equilibrium
Troposphere Area of the earths atmosphere located between the surface and 10km
T-Shaped A type of molecular geometry stemming from the trigonal bipyramidal electron geometry.  The shape looks like a T



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Uncertainty Principle You can never know both the position and momentum of anything (subatomic particles - from Heisenberg)
Unimolecular Reaction A chemical reaction in which there is only one reactant
Unit A standard value that describes a quantity
Unit Cell In a large substance, it is the simplest repeating pattern



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Valence Electrons The electrons that are in the outer-most shell of an atom, and are therefore involved in bonding
VSEPR (Valence Shell Electron Pair Repulsion) Theory that places electrons as far apart as is possible in order to reduce their electron-electron repulsion
Vapor Pressure A partial pressure of a substance in a liquid phase in order to maintain equilibrium
Viscosity How "thick" a liquid is, or how much it resists flow
Visible Light Light (photons) that the human eye can see, located between 400 and 700 nm
Volt (V) Standard unit used to describe electrical potential
Volume How much space is taken up by something
Volumetric Flask A container that has been calibrated to contain a very specific volume of a liquid



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Water Equilibrium Constant (Kw) Kw = 1x10-14 = [H3O+] [OH-].  An equilibrium constant describing the transfer of H+ between two water molecules
Wave Described by amplitude (height), wavelength, and frequency
Wavelength The distance between the same point on 2 subsequent waves
Weak Acid An acid that only partially dissociates with its H+ according to Bronsted-Lowry Acid/Base Theory
Weak Base A base that only partially associates with H+ according to the Bronsted-Lowry Acid/Base Theory
Work (w) The amount of energy used (transferred) by a force in order to displace something, w = fd



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I have no words to define for X-Z... If you have any words you'd like defined here, please let me know!


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