Glossary
- Page ID
- 482420
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| (Eg. "Genetic, Hereditary, DNA ...") | (Eg. "Relating to genes or heredity") |  |
The infamous double helix | https://bio.libretexts.org/ | CC-BY-SA; Delmar Larsen |
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Word(s) |
Definition |
Image | Caption | Source |
|---|---|---|---|---|
| 5% rule | when calculating equilibrium concentrations, if the change in concentration is less than 5% of the initial concentrations, then the change can be mathematically disregarded | |||
| Absolute zero | 0 K or –273 °C; the lowest possible temperature | |||
| Absorption spectrum | spectrum produced by the emission of light by atoms as an electron moves from a lower energy level to a higher energy level | |||
| Acid ionization | reaction involving the transfer of a proton from an acid to water, yielding hydronium ions and the conjugate base of the acid | |||
| Acid ionization constant (Ka) | equilibrium constant for the ionization of a weak acid | |||
| Acid-base titration curve | plot of the pH of a solution of acid or base versus the volume of base or acid added during a titration | |||
| Acidic aqueous solution | solution for which water is the solvent and the concentration of hydronium ions ([H3O+]) is greater than the concentration of hydroxide ions ([OH-]), resulting a pH value less than 7 | |||
| Actinide | element of the set of transition metals located below the main table, with lanthanides | |||
| Activation energy (Ea) | energy necessary in order for a reaction to take place | |||
| Active electrode | electrode that participates in the oxidation-reduction reaction of an electrochemical cell; the mass of an active electrode changes during the oxidation-reduction reaction | |||
| Actual yield | amount of product formed in a reaction | |||
| Alkali metal | element in group 1 | |||
| Alkaline earth metal | element in group 2 | |||
| Amphiprotic | species that may either gain or lose a proton in a reaction | |||
| Amplitude | extent of the displacement caused by a wave; for sinusoidal waves, it is one-half the difference from the peak height to the trough depth, and the intensity is proportional to the square of the amplitude | |||
| Angular momentum quantum number (l) | quantum number distinguishing the different shapes of orbitals; it is also a measure of the orbital angular momentum | |||
| negatively charged atom or molecule (contains more electrons than protons) | ||||
| electrode in an electrochemical cell at which oxidation occurs; information about the anode is recorded on the left side of the salt bridge in cell notation | ||||
| Arrhenius equation | mathematical relationship between the rate constant and the activation energy of a reaction | |||
| Atmospheric pressure | the pressure exerted by the gases in Earth's atmosphere; approximately 101 kPa (1 atm) at sea level | |||
| Atmosphere (atm) | unit of pressure; 1 atm = 101,325 Pa | |||
| smallest particle of an element that can enter into a chemical combination | ||||
| Atomic mass | average mass of atoms of an element, expressed in amu | |||
| Atomic mass unit (amu) | unit of mass equal to 1/12 of the mass of a 12C atom; also called unified atomic mass unit (u) or Dalton (Da) | |||
| Atomic number (Z) | number of protons in the nucleus of an atom | |||
| Atomic orbital | region of space where an electron is most likely found, described by quantum numbers | |||
| Aufbau principle | dictates the procedure in which the electron configuration of the elements is determined by “building” them in order of atomic numbers, adding one proton to the nucleus and one electron to the proper subshell at a time | |||
| Autoionization | reaction between identical species yielding ionic products; for water, this reaction involves transfer of protons to yield hydronium and hydroxide ions | |||
| Average kinetic energy (KEavg) | The mean kinetic energy of particles in a gas; directly proportional to temperature | |||
| Average rate of reaction | rate of a chemical reaction computed as the ratio of a measured change in amount or concentration of substance to the time interval over which the change occurred | |||
| Avogadro's number (NA) | experimentally determined value of the number of entities comprising 1 mole of substance, equal to 6.022 × 1023 mol−1 | |||
| Axial position | location in a trigonal bipyramidal geometry in which there is another atom at a 180° angle and the equatorial positions are at a 90° angle | |||
| Balanced chemical equation | chemical equation with equal numbers of atoms for each element in the reactant and product | |||
| Ball-and-stick model | 3D representation of molecules using spheres for atoms and sticks for bonds | |||
| Barometer | device used to measure atmospheric pressure in millimeters of mercury (mmHg) or torr | |||
| Base ionization | reaction involving the transfer of a proton from water to a base, yielding hydroxide ions and the conjugate acid of the base | |||
| Base ionization constant (Kb) | equilibrium constant for the ionization of a weak base | |||
| Basic aqueous solution | solution for which water is the solvent and the concentration of hydroxide ions ([OH-]) is greater than the concentration of hydronium ions ([H3O+]), resulting a pH value greater than 7 | |||
| Bimolecular elementary reaction | reaction that involves the collision of two reactant particles | |||
| Binary acid | compound that contains hydrogen and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ ions when dissolved in water) | |||
| Binary ionic compound | ionic compound containing two different elements, one metal and one nonmetal | |||
| Binding energy | the minimum energy required to remove an electron from an atom, result in an ion; also called ionization energy or threshold energy | |||
| Boiling point | temperature at which the vapor pressure of a liquid equals the pressure of the gas above it | |||
| Bomb calorimeter | device designed to measure the energy change for processes occurring under conditions of constant volume; commonly used for reactions involving solid and gaseous reactants or products | |||
| Bond angle | the angle between two bonds that share an atom, measured in degrees | |||
| Bond dipole moment | separation of charge in a bond that depends on the difference in electronegativity and the bond distance represented by partial charges or a vector | |||
| Bond distance | distance between the nuclei of two bonded atoms, typically measured in Ångstroms or picometers; also called bond length | |||
| Bond energy | energy required to break a covalent bond in a gaseous substance; also called bond dissociation energy | |||
| Brønsted-Lowry acid | proton donor | |||
| Brønsted-Lowry base | proton acceptor | |||
| mixture of a weak acid or a weak base and the salt of its conjugate; the pH of a buffer resists change when small amounts of acid or base are added | ||||
| Buffer capacity | amount of an acid or base that can be added to a volume of a buffer solution before its pH changes significantly (usually by one pH unit) | |||
| Calorie (cal) | unit of heat or other energy; the amount of energy required to raise 1 gram of water by 1 degree Celsius; 1 cal is defined as 4.184 J | |||
| Calorimetry | process of measuring the amount of heat involved in a chemical or physical process | |||
| substance that increases the rate of a reaction without itself being consumed by the reaction | ||||
| electrode in an electrochemical cell at which reduction occurs; information about the cathode is recorded on the right side of the salt bridge in cell notation | ||||
| Cathodic protection | method of protecting metal by using a sacrificial anode and effectively making the metal that needs protecting the cathode, thus preventing its oxidation | |||
| positively charged atom or molecule (contains fewer electrons than protons) | ||||
| Cell notation | shorthand way to represent the reactions in an electrochemical cell | |||
| Cell potential (Ecell) | difference in electrical potential that arises when dissimilar metals are connected; the driving force for the flow of charge (current) in oxidation-reduction reactions; also called electromotive force (EMF) | |||
| Celsius (°C) | unit of temperature; water freezes at 0 °C and boils at 100 °C on this scale | |||
| Chalcogen | element in group 16 | |||
| Chemical activity (a) | unitless measure of concentration reflecting moderating effects such as attractions and repulsions between molecules | |||
| Chemical energy | the energy associated with the arrangement of atoms in a substance | |||
| Chemical equation | symbolic representation of a chemical reaction | |||
| Chemical equilibrium | in chemical reactions, the state in which the conversion of reactants into products and the conversion of products back into reactants occur simultaneously at the same rate; state of balance | |||
| Chemical reaction | a process in which atoms are rearranged to form new substances with new properties | |||
| Chemical symbol | one-, two-, or three-letter abbreviation used to represent an element or its atoms | |||
| study of the composition, properties, and interactions of matter | ||||
| Coefficient | number placed in front of symbols or formulas in a chemical equation to indicate their relative amount | |||
| Collision theory | model that emphasizes the energy and orientation of molecular collisions to explain and predict reaction kinetics | |||
| Common ion effect | effect on equilibrium when a substance with an ion in common with the dissolved species is added to the solution; causes a decrease in the solubility of an ionic species, or a decrease in the ionization of a weak acid or base | |||
| pure substance that can be decomposed into two or more elements | ||||
| qualitative term for a solution containing solute at a relatively high concentration | ||||
| quantitative measure of the relative amounts of solute and solvent present in a solution | ||||
| Concentration cell | galvanic cell in which the two half-cells are the same except for the concentration of the solutes; spontaneous when the overall reaction is the dilution of the solute | |||
| Conjugate acid | substance formed when a base gains a proton | |||
| Conjugate base | substance formed when an acid loses a proton | |||
| Conjugate pair | pair of Brønsted-Lowry acid and its conjugate base or base and its conjugate acid | |||
| Constant-pressure calorimeter | calorimeter in which the pressure remains constant because the system is open to the atmosphere | |||
| Constant-volume calorimeter | calorimeter in which the volume remains constant, creating a closed system often used for non-gases | |||
| Constructive interference | occurs when the peaks of two electromagnetic waves align ("in phase") and their amplitudes add together, resulting in brighter light | |||
| Corrosion | degradation of metal through an electrochemical process | |||
| Covalent bonding | occurs when electrons are shared between atoms in a molecule or a polyatomic ion; most often occurs between nonmetals | |||
| Covalent compound | compound composed of molecules formed by atoms of two or more different elements | |||
| Covalent radius | one-half the distance between the nuclei of two identical bonded atoms | |||
| Critical point | temperature and pressure above which a gas cannot be condensed into a liquid | |||
| Current | flow of electrical charge; the SI unit of charge is the coulomb (C) and current is measured in amperes | |||
| d orbital | region of space with high electron density that is either four-lobed or contains a dumbbell and torus shape; describes orbitals with l = 2; an electron in this orbital is called a d electron | |||
| Dalton's law of partial pressures | states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the individual gases | |||
| Density | ratio of mass to volume for a substance or object | |||
| Deposition | change from a gaseous state directly to a solid state | |||
| Derived SI unit | units derived from the seven SI base units | |||
| Destructive interference | occurs when the peak of one electromagnetic wave aligns with the trough of another ("out of phase") and their amplitudes cancel out, resulting in a smaller wave or no wave | |||
| Diffraction | redirection of electromagnetic radiation that occurs when it encounters a physical barrier of appropriate dimensions | |||
| Diffusion | the movement of gas particles from an area of higher concentration to an area of lower concentration | |||
| qualitative term for a solution containing solute at a relatively low concentration | ||||
| Dilution | process of adding solvent to a solution in order to lower the concentration of solutes | |||
| Dipole moment | property of a molecule that describes the separation of charge determined by the sum of the individual bond moments based on the molecular structure | |||
| Dipole-dipole attraction | intermolecular attraction between two permanent dipoles | |||
| Dispersion force | attraction between two rapidly fluctuating, temporary dipoles; significant only when particles are very close together; also called London dispersion force | |||
| Dissociation | physical process accompanying the dissolution of an ionic compound in which the compound’s constituent ions are solvated and dispersed throughout the solution | |||
| Dissolution | the process by which solute components are dispersed in a solvent | |||
| Double bond | covalent bond in which two pairs of electrons are shared between two atoms | |||
| Double slit experiment | investigation into the diffraction of light when waves pass through narrow slits, resulting in an interference pattern showing that light behaves as a wave | |||
| Effective nuclear charge (Zeff) | charge that leads to the Coulomb force exerted by the nucleus on an electron, calculated as the nuclear charge minus shielding | |||
| Effusion | the movement of gas particles through an opening smaller than the mean free path of the particles into an evacuated space | |||
| Electrical work (welectric) | negative of total charge times the cell potential; equal to wmax for the system, and so equals the free energy change (ΔG) | |||
| Electrochemistry | the study of the relationship between chemical reactions and electron flow | |||
| Electrolysis | process that uses electrical energy to drive a nonspontaneous redox reaction | |||
| Electrolytic cell | electrochemical cell with two electrodes in a single compartment where an external power source supplies electrical energy, generating a potential difference that forces electrons to flow and drives a nonspontaneous redox reaction | |||
| Electromagnetic radiation | energy transmitted by waves that have an electric-field component and a magnetic-field component | |||
| Electromagnetic spectrum | range of energies that electromagnetic radiation can comprise, including radio, microwaves, infrared, visible, ultraviolet, X-rays, and gamma rays; since electromagnetic radiation energy is proportional to the frequency and inversely proportional to the wavelength, the spectrum can also be specified by ranges of frequencies or wavelengths | |||
| negatively charged, subatomic particle of relatively low mass located outside the nucleus | ||||
| Electron-deficient molecule | molecule containing a central atom without a filled valence shell | |||
| Electron configuration | electronic structure of an atom in its ground state given as a listing of the orbitals occupied by the electrons | |||
| Electron density | a measure of the probability of locating an electron in a particular region of space, it is equal to the squared absolute value of the wave function ψ | |||
| Electron shielding | occurs when inner electrons partially block the nuclear charge from outer electrons, reducing the effective nuclear charge (Zeff) | |||
| Electronegativity | tendency of an atom to attract electrons in a bond to itself | |||
| Electroplating | coating objects with a thin metal layer via electrolysis | |||
| Electrostatic attraction | attraction between an atom's positively charged nucleus and the negatively charged electrons of another atom | |||
| substance that is composed of a single type of atom; a substance that cannot be decomposed by a chemical change | ||||
| Elementary reaction | step in a reaction mechanism that explicitly shows which particles collide, break apart, or rearrange to form the products and/or intermediates | |||
| Emission spectrum | spectrum produced by the emission of light by atoms as an electron moves from a higher energy level to a lower energy level | |||
| Empirical formula | formula showing the composition of a compound given as the simplest whole-number ratio of atoms | |||
| Endothermic | describes a chemical reaction or physical change that absorbs heat | |||
| Endpoint | measured volume of titrant solution that yields the change in sample solution appearance or other property expected for stoichiometric equivalence (see equivalence point) | |||
| capacity to supply heat or do work | ||||
| Enthalpy (H) | sum of a system’s internal energy and the mathematical product of its pressure and volume | |||
| Enthalpy change (ΔH) | heat released or absorbed by a system under constant pressure during a chemical or physical process | |||
| Entropy (S) | state function that is a measure of the matter and/or energy dispersal within a system, determined by the number of system microstates often described as a measure of the disorder of the system | |||
| Entropy change (ΔS) | increase or a decrease in the dispersal of energy in the system during a chemical or physical change | |||
| Enzyme | biological catalyst; usually large protein molecules with a small active site that binds the substrate and carries out the reaction | |||
| Equatorial position | one of the three positions in a trigonal bipyramidal geometry with 120° angles between them; the axial positions are located at a 90° angle | |||
| Equilibrium constant (K) | value of the reaction quotient for a system at equilibrium | |||
| Equivalence point | volume of titrant solution required to react completely with the analyte in a titration analysis; provides a stoichiometric amount of titrant for the sample’s analyte according to the titration reaction | |||
| Exact number | number derived by counting or by definition | |||
| Excess reactant | reactant present in an amount greater than required by the reaction stoichiometry | |||
| Excited state | state having an energy greater than the ground-state energy | |||
| Exothermic | describes a chemical reaction or physical change that releases heat | |||
| Expansion work (pressure-volume work) | type of mechanical work done as a system expands or contracts against external pressure | |||
| f orbital | multi-lobed region of space with high electron density, describes orbitals with l = 3; an electron in this orbital is called an f electron | |||
| Faraday's constant (F) | charge on 1 mol of electrons; F = 96,485 C/mol e− | |||
| First law of thermodynamics | internal energy of a system changes due to heat flow in or out of the system or work done on or by the system; also called the law of conservation of energy | |||
| Formula unit | the simplest ratio of ions in an ionic compound | |||
| Free radical | molecule that contains an odd number of electrons | |||
| Freezing | change from a liquid state to a solid state | |||
| Frequency (v) | the number of wave cycles that pass a specified point in space in a specified amount of time; unit expressed as cycles per second (s-1) or hertz (Hz) | |||
| Frequency factor (A) | proportionality constant in the Arrhenius equation, related to the relative number of collisions having an orientation capable of leading to product formation | |||
| Fuel cell | galvanic cell that continuously converts chemical energy into electrical energy as long as fuel and an oxidant are supplied | |||
| Galvanic cell | electrochemical cell that turns chemical energy into electrical energy using spontaneous redox reactions; also called a voltaic cell | |||
| state in which matter has neither definite volume nor shape | ||||
| Gibbs free energy (G) | thermodynamic property defined in terms of system enthalpy and entropy, allowing the prediction of spontaneity | |||
| Gibbs free energy change (ΔG) | the amount of energy available that can harnessed to do useful work in a thermodynamic system; equal to the sum of the enthalpy plus the product of the temperature and entropy of the system; can predict direction of chemical reaction under constant temperature and pressure | |||
| Ground state | state in which the electrons in an atom, ion, or molecule have the lowest energy possible | |||
| Group | vertical column of the periodic table | |||
| Half-life of a reaction (t1/2) | time required for half of a given amount of reactant to be consumed | |||
| Half-reaction method | method that produces a balanced overall oxidation-reduction reaction by splitting the reaction into an oxidation “half” and reduction “half,” balancing the two half-reactions, and then combining the oxidation half-reaction and reduction half-reaction in such a way that the number of electrons generated by the oxidation is exactly canceled by the number of electrons required by the reduction | |||
| Halogen | element in group 17 | |||
| Heat (q) | transfer of thermal energy between two bodies | |||
| Heat capacity (C) | extensive property of a body of matter that represents the quantity of heat required to increase its temperature by 1 degree Celsius (or 1 kelvin) | |||
| Heating/cooling curve | graph illustrating how the temperature of a substance changes as it absorbs or releases heat | |||
| Heisenberg uncertainty principle | rule stating that it is impossible to exactly determine both certain conjugate dynamical properties such as the momentum and the position of a particle at the same time; the uncertainty principle is a consequence of quantum particles exhibiting wave–particle duality | |||
| Henderson-Hasselbalch equation | equation used to calculate the pH of buffer solutions | |||
| Hertz (Hz) | the SI unit of frequency, which is the number of cycles per second, s−1 | |||
| Hess's law | rule stating that if a process can be represented as the sum of several steps, the enthalpy change of the process equals the sum of the enthalpy changes of the steps | |||
| Heterogeneous catalyst | catalyst present in a different phase from the reactants, furnishing a surface at which a reaction can occur | |||
| Heterogeneous equilibrium | equilibrium between reactants and products in different phases | |||
| Homogeneous catalyst | catalyst present in the same phase as the reactants | |||
| Homogeneous equilibrium | equilibrium within a single phase | |||
| Homogeneous mixture | combination of substances with a composition that is uniform throughout | |||
| Hund's rule | every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin | |||
| Hydrogen bonding | occurs when exceptionally strong dipoles attract; bonding that exists when hydrogen is bonded to one of the three most electronegative elements: F, O, or N | |||
| Hypervalent compound | molecule containing at least one main group element that has more than eight electrons in its valence shell | |||
| ICE table | method of calculating equilibrium concentration by tracking how a system moves from its initial concentration (I) through the changes (C) to equilibrium (E) | |||
| hypothetical gas that behaves exactly as predicted by the ideal gas law | ||||
| Ideal gas law | describes the behaviour of gases under many conditions; \(PV = nRT\) | |||
| Induced dipole | temporary dipole formed when the electrons of an atom or molecule are distorted by the instantaneous dipole of a neighboring atom or molecule | |||
| Induced-fit model | model of enzyme function where the enzyme and substrate adjust their shapes upon bindng to improve the fit | |||
| Inert electrode | electrode that allows current to flow, but that does not otherwise participate in the oxidation-reduction reaction in an electrochemical cell; the mass of an inert electrode does not change during the oxidation-reduction reaction; inert electrodes are often made of platinum or gold because these metals are chemically unreactive | |||
| Initial rate of reaction | instantaneous rate of a chemical reaction at t = 0 s (immediately after the reaction has begun) | |||
| Instantaneous rate of reaction | rate of a chemical reaction at any instant in time, determined by the slope of the line tangential to a graph of concentration as a function of time | |||
| Integrated rate law | equation that relates the concentration of a reactant to elapsed time of reaction | |||
| Interference pattern | pattern typically consisting of alternating bright and dark fringes; it results from constructive and destructive interference of waves | |||
| Intermolecular force | noncovalent attractive force between atoms, molecules, and/or ions | |||
| Internal energy (E) | total of all possible kinds of energy present in a substance or substances | |||
| electrically charged atom or molecule (contains unequal numbers of protons and electrons) | ||||
| Ion product of water (Kw) | equilibrium constant for the autoionization reaction of water | |||
| Ion-dipole attraction | electrostatic attraction between an ion and a polar molecule | |||
| Ionic bonding | occurs when a metal donates one or more electrons to a nonmetal, forming oppositely charged ions | |||
| Ionic compound | compound composed of cations and anions combined in ratios, yielding an electrically neutral substance | |||
| Ionic radius | measure of an ion's size, where cations are larger than the parent atom and anions are smaller | |||
| Ionic solid | solid composed of positive and negative ions held together by strong electrostatic attractions | |||
| Isoelectronic | describes a group of ions or atoms that have identical electron configurations | |||
| Isotope | atom that contains the same number of protons but different number of neutrons | |||
| Joule (J) | SI unit of energy; 1 joule is the kinetic energy of an object with a mass of 2 kilograms moving with a velocity of 1 meter per second; 1 J = 1 kg m2/s and 4.184 J = 1 cal | |||
| equilibrium constant for reactions based on concentrations of reactants and products | ||||
| Kelvin (K) | SI unit of temperature; 273.15 K = 0 ºC | |||
| Kinetic energy | the energy of motion | |||
| Kinetic molecular theory | microscopic model explaining ideal gas behavior, postulating that gas particles move in straight lines unless interrupted by elastic collisions, particles are of negligible volume, particles' average kinetic energy is proportional to temperature, and gas pressure results from collisions with the container walls | |||
| equilibrium constant for gas-phase reactions based on partial pressures of reactants and products | ||||
| Lanthanide | element of the set of transition metals located below the main table, with actinides | |||
| Law of conservation of mass | states that atoms are neither created nor destroyed in a chemical reaction, but rather rearranged | |||
| Law of mass action | when a reversible reaction has attained equilibrium at a given temperature, the reaction quotient remains constant | |||
| Le Chatelier's principle | when a chemical system at equilibrium is disturbed, it returns to equilibrium by counteracting the disturbance | |||
| Lewis acid | substance that can accept a pair of electrons | |||
| Lewis base | substance that can donate a pair of electrons | |||
| Lewis structure | diagram showing lone pairs and bonding pairs of electrons in a molecule or an ion | |||
| Limiting reactant | reactant present in an amount lower than required by the reaction stoichiometry, thus limiting the amount of product generated | |||
| Line spectrum | electromagnetic radiation emitted at discrete wavelengths by a specific atom (or atoms) in an excited state | |||
| Linear geometry | shape in which two outside groups are placed on opposite sides of a central atom | |||
| state of matter that has a definite volume but indefinite shape | ||||
| Lock-and-key model | model of enzyme function where the substrate fits precisely into the enzyme’s active site | |||
| Lone pair | two (a pair of) valence electrons that are not used to form a bond | |||
| Macroscopic realm | everyday things that are large enough to sense directly by human sight and touch | |||
| Magnetic quantum number (ml) | quantum number signifying the orientation of an atomic orbital around the nucleus; orbitals having different values of ml but the same subshell value of l have the same energy (are degenerate), but this degeneracy can be removed by application of an external magnetic field | |||
| Manometer | device used to measure the pressure of a gas trapped in a container, either relative to a vacuum (closed-end) or to atmospheric pressure (open-end) | |||
| fundamental property indicating amount of matter | ||||
| Mass number (A) | sum of the numbers of neutrons and protons in the nucleus of an atom | |||
| anything that occupies space and has mass | ||||
| Maxwell-Boltzmann distribution | function demonstrating the relative number of particles in a gas sample that move at a given speed | |||
| Mean free path | the average distance travelled between gas particle collisions | |||
| Melting | change from a solid state to a liquid state | |||
| Melting point | temperature at which the solid and liquid phases of a substance are in equilibrium | |||
| element that is shiny, malleable, good conductor of heat and electricity | ||||
| Metallic bonding | occurs when valence electrons are delocalized across many atoms in a metal, forming a "sea of electrons" that allows metals to conduct electricity and be malleable | |||
| Metalloid | element that has properties that are between those of metals and nonmetals; these elements are typically semiconductors | |||
| Method of initial rates | use of a more explicit algebraic method to determine the orders in a rate law | |||
| Michaelis-Menten mechanism | describes how enzymes catalyze reactions through a two-step process; an enzyme binds a substrate to form an enzyme-substrate complex, which then breaks down to release the product while regenerating the enzyme | |||
| Microscopic realm | things that are much too small to be sensed directly | |||
| Microstate (W) | possible configuration or arrangement of matter and energy within a system | |||
| Midpoint | point on a titration curve halfway between start of the curve and the equivalence point, or between equivalence points in a polyprotic titration | |||
| Molar heat capacity (Cm) | amount of energy needed to increase the temperature of 1 mol of a substance by 1°C; measured in J/(mol °C) | |||
| mass in grams of 1 mole of a substance | ||||
| Molarity (M) | unit of concentration, defined as the number of moles of solute dissolved in 1 liter of solution | |||
| amount of substance containing the same number of atoms, molecules, ions, or other entities as the number of atoms in exactly 12 grams of 12C | ||||
| Mole ratio | unit conversation factor that relates the number of moles of substances in a balanced chemical equation | |||
| Molecular formula | formula indicating the composition of a molecule of a compound and giving the actual number of atoms of each element in a molecule of the compound | |||
| Molecular structure | structure that includes only the placement of the atoms in the molecule | |||
| bonded collection of two or more atoms of the same or different elements | ||||
| Monoprotic acid | acid containing one ionizable hydrogen atom per molecule | |||
| Nernst equation | equation that relates the logarithm of the reaction quotient (Q) to nonstandard cell potentials; can be used to relate equilibrium constants to standard cell potentials | |||
| Neutral aqueous solution | solution for which water is the solvent and the concentration of hydronium ions ([H3O+]) is equal to the concentration of hydroxide ions ([OH-]), resulting a pH value of 7 | |||
| Neutralization reaction | reaction in which an acid and a base react to form a salt and water | |||
| Neutron | uncharged, subatomic particle located in the nucleus | |||
| Nobel Prize in Chemistry | prestigious international award recognizing groundbreaking contributions to the field of chemistry | |||
| Noble gas | element in group 18; also called inert gas | |||
| Node | any point of a standing wave with zero amplitude; also regions of an orbital where the probability of finding an electron is zero | |||
| element that appears dull, poor conductor of heat and electricity | ||||
| Nonspontaneous process | process that requires continual input of energy from an external source | |||
| Normal boiling point | temperature at which a liquid’s vapor pressure equals 1 atm (760 torr) | |||
| Nuclear energy | the energy stored in the nucleus of an atom, which can be released during nuclear reactions | |||
| Nucleus | massive, positively charged center of an atom made up of protons and neutrons | |||
| Octahedral geometry | shape in which six outside groups are placed around a central atom such that a three-dimensional shape is generated, with four groups forming a square and the other two forming the apex of two pyramids, one above and one below the square plane | |||
| Octet rule | guideline that states main group atoms will form structures in which eight valence electrons interact with each nucleus, counting bonding electrons as interacting with both atoms connected by the bond | |||
| Orbital diagram | pictorial representation of the electron configuration showing each orbital as a box and each electron as an arrow | |||
| Overall reaction order | sum of the reaction orders for each substance represented in the rate law | |||
| Overpotential | the extra voltage beyond the theoretical potential that is required to make a reaction occur at a practical rate | |||
| Oxidation | process in which a species loses electrons | |||
| Oxidation half-reaction | the “half” of an oxidation-reduction reaction involving oxidation; the half-reaction in which electrons appear as products; balanced when each atom type, as well as the charge, is balanced | |||
| Oxidation number | tool to keep track of electron transfer during redox reactions, increasing upon oxidation and decreasing upon reduction; also called oxidation state | |||
| Oxidation-reduction reaction | broad type of reaction where one substance loses electrons through oxidation and another gains electrons through reduction; also called a redox reaction | |||
| Oxidizing agent | the species that accepts electrons from the other reactant and is itself reduced | |||
| Oxoacid | compound containing a nonmetal and one or more hydroxyl groups; also called oxyacid | |||
| p orbital | dumbbell-shaped region of space with high electron density, describes orbitals with l = 1; an electron in this orbital is called a p electron | |||
| Parallel lines | lines in the same plane that do not intersect | |||
| Partial pressure | pressure exerted by an individual gas in a mixture of gases, independent of the pressures exerted by other gases | |||
| Pascal (Pa) | SI unit of pressure; 1 Pa = 1 N/m2 | |||
| Pauli exclusion principle | specifies that no two electrons in an atom can have the same value for all four quantum numbers | |||
| Penetration | the extent to which an electron in a subshell can approach the nucleus | |||
| Percent ionization | measure of acid or base strength; ratio of the concentration of the ionized acid/base to the initial acid/base concentration, multiplied by 100 | |||
| Percent yield | measure of the efficiency of a reaction, expressed as a percentage of the theoretical yield | |||
| Period | horizontal row of the periodic table; also called a series | |||
| Perpendicular lines | lines in the same plane that form a right angle | |||
| logarithmic measure of the concentration of hydronium ions in a solution | ||||
| pH indicator | organic acid or base whose color changes depending on the pH of the solution it is in; permits visual detection of endpoint; also called acid-base indicator | |||
| Phase change | when a substance transitions between solid, liquid, and gas phases; also called phase transition | |||
| Phase diagram | pressure-temperature graph summarizing conditions under which the phases of a substance can exist | |||
| Photoelectric effect | the ejection of electrons from a metal's surface when irradiated by light above its threshold frequency | |||
| Photon | smallest possible packet of electromagnetic radiation, a particle of light | |||
| Pnictogen | element of group 15 | |||
| logarithmic measure of the concentration of hydroxide ions in a solution | ||||
| Polar covalent bond | covalent bond between atoms of different electronegativities; a covalent bond with a positive end and a negative end | |||
| Polar molecule | molecule with an overall dipole moment | |||
| Polyatomic ion | ion composed of more than one atom | |||
| Polyprotic acid | acid with more than one ionizable proton per molecule, undergoing stepwise ionization | |||
| Polyprotic base | base that can accept more than one proton, undergoing stepwise protonation | |||
| Potential energy | stored energy due to position or arrangement | |||
| Precipitation | the process of dissolved ions in an aqueous solution reacting to form a solid precipitate | |||
| force exerted per unit area | ||||
| Principal quantum number (n) | quantum number specifying the shell an electron occupies in an atom | |||
| substance formed by a chemical or physical change; shown on the right side of the arrow in a chemical equation | ||||
| Proton | positively charged, subatomic particle located in the nucleus | |||
| Pure covalent bond | covalent bond between atoms of identical electronegativities; also called a nonpolar covalent bond | |||
| Quantization | occurring only in specific discrete values, not continuous | |||
| Quantum mechanical model | Schrödinger's model of the atom treating electrons as three-dimensional waves spread out in a probability cloud (orbital) around the nucleus | |||
| Radial probability | the probability of finding an electron at a specific distance, r, from the nucleus | |||
| Radiant energy | the energy carried by electromagnetic waves | |||
| Rate constant (k) | proportionality constant in the relationship between reaction rate and concentrations of reactants | |||
| Rate determining step | the slowest step in the reaction mechanism; determines the overall reaction rate | |||
| Rate law | mathematical equation showing the dependence of reaction rate on the rate constant and the concentration of one or more reactants; also called rate equation | |||
| Reactant | substance undergoing a chemical or physical change; shown on the left side of the arrow in a chemical equation | |||
| Reaction energy diagram | diagram that illustrates how energy changes during a reaction, including the transition states, activation energy barriers, and overall enthalpy change | |||
| Reaction intermediate | species with fully formed bonds that appears as a product in one step but is consumed in a subsequent step | |||
| Reaction mechanism | step-by-step series of simpler reactions by which an overall reaction takes place | |||
| Reaction order | value of an exponent in a rate law, expressed as an ordinal number (for example, zero order for 0, first order for 1, second order for 2, and so on) | |||
| Reaction quotient (Q) | ratio of the product of molar concentrations (or pressures) of the products to that of the reactants, each concentration (or pressure) being raised to the power equal to the coefficient in the equation | |||
| Reaction rate | measure of the speed at which a chemical reaction takes place | |||
| Reducing agent | the species that provides electrons to the other reactant and is itself oxidized | |||
| Reduction | process in which a species gains electrons | |||
| Reduction half-reaction | the “half” of an oxidation-reduction reaction involving reduction; the half-reaction in which electrons appear as reactants; balanced when each atom type, as well as the charge, is balanced | |||
| Reversible reaction | chemical reaction that can proceed in both the forward and reverse directions under given conditions | |||
| Root mean square velocity (urms) | the square root of the average of the squared velocities of particles in a gas | |||
| s orbital | spherical region of space with high electron density, describes orbitals with l = 0; an electron in this orbital is called an s electron | |||
| Salt bridge | galvanic cell component allowing ions to move between the half-cells to maintain electrical neutrality and preventing charge buildup | |||
| Salts | ionic compounds composed of cations and anions, either of which may react with water as acids or bases | |||
| Schrödinger equation | A mathematical framework developed by Erwin Schrödinger that describes the wave-like behavior of electrons; this equation can predict the energy levels of hydrogen, resulting in quantum numbers that define the properties of hydrogen orbitals | |||
| Scientific notation | a convenient method of expressing very large or very small numbers often used by scientists | |||
| Second law of thermodynamics | entropy of the universe increases for a spontaneous process | |||
| Shell | set of orbitals with the same principal quantum number, n | |||
| SI unit (International System of Units) | standards fixed by international agreement in the International System of Units (Le Système International d’Unités) | |||
| Significant figures | all of the measured digits in a determination, including the uncertain last digit; also called significant digits | |||
| Single bond | bond in which a single pair of electrons is shared between two atoms | |||
| state of matter that is rigid, has a definite shape, and has a fairly constant volume | ||||
| Solubility equilibrium | equilibrium established when dissolution of a dissolving solid and precipitation of its ions happen at equal rates | |||
| Solubility product constant (Ksp) | equilibrium constant for a solid substance dissolving in an aqueous solution | |||
| Solute | solution component present in a concentration less than that of the solvent | |||
| a homogeneous mixture consisting of one or more solutes dissolved in a solvent | ||||
| Solvent | solution component present in a concentration that is higher relative to other components | |||
| Space-filling model | 3D representation of molecules using spheres to show the relative size of atoms and how they fill space | |||
| Specific heat capacity (c) | intensive property of a substance that represents the quantity of heat required to raise the temperature of 1 gram of the substance by 1 degree Celsius (or 1 kelvin) | |||
| Speed | the distance a wave travels per unit time, measured in meters per second (m/s); the speed of a wave is equal to the product of its wavelength and frequency | |||
| Spin quantum number (ms) | number specifying the electron spin direction, either +1/2 or -1/2 | |||
| Spontaneous process | physical or chemical change that occurs without the addition of energy from an external source | |||
| Standard cell potential (E°cell) | the cell potential when all reactants and products are in their standard states (1 bar or 1 atm or gases; 1 M for solutes), usually at 298.15 K; can be calculated by subtracting the standard reduction potential for the half-reaction at the anode from the standard reduction potential for the half-reaction occurring at the cathode | |||
| Standard enthalpies of formation (ΔH°f) | enthalpy change of a chemical reaction in which 1 mole of a pure substance is formed from its elements in their most stable states under standard state conditions | |||
| Standard entropy change (ΔS°) | change in entropy for a reaction calculated using the standard entropies, usually at room temperature | |||
| Standard free energies of formation (ΔG°f) | change in free energy accompanying the formation of one mole of substance from its elements in their standard states | |||
| Standard free energy change (ΔG°) | change in free energy for a process occurring under standard conditions (1 bar pressure for gases, 1 M concentration for solutions) | |||
| Standard hydrogen electrode (SHE) | the electrode consists of hydrogen gas bubbling through hydrochloric acid over an inert platinum electrode whose reduction at standard conditions is assigned a value of 0 V; the reference point for standard reduction potentials | |||
| Standard molar entropy (S°) | entropy of 1 mol of substance at a standard pressure of 1 atm | |||
| Standard molar volume | the volume one mole of an ideal gas occupies at STP, defined as 22.4 L | |||
| Standard oxidation potential (E°ox) | measures how readily a substance loses electrons under standard conditions; the negative of the standard reduction potential for the reverse reaction | |||
| Standard reduction potential (E°red) | measures how readily a species gains electrons under standard conditions (1 bar or 1 atm for gases; 1 M for solutes) usually at 298.15 K; tabulated values used to calculate standard cell potentials | |||
| Standard state conditions | set of physical conditions as accepted as common reference conditions for reporting thermodynamic properties; 1 bar of pressure, and solutions at 1 molar concentrations, usually at a temperature of 298.15 K | |||
| Standard temperature and pressure (STP) | 273.15 K (0.00°C) and 1 atm; universal standard conditions used to compare gas properties | |||
| Standing wave | localized wave phenomenon characterized by discrete wavelengths determined by the boundary conditions used to generate the waves; standing waves are inherently quantized; also called stationary wave | |||
| State function | property depending only on the state of a system, and not the path taken to reach that state | |||
| Stock solution | solution of a desired concentration diluted from a more concentrated one | |||
| Stoichiometry | the quantitative relationships between substances in a balanced chemical reaction | |||
| Strong acid | acidic substance that dissociates completely into ions in water | |||
| Strong base | basic substance that dissociates completely into ions in water | |||
| Structural formula | shows the atoms in a molecule and how they are connected | |||
| Sublimation | change from solid state directly to gaseous state | |||
| Subshell | set of orbitals in an atom with the same values of n and l | |||
| Substrate | reactant in an enzyme-catalyzed reaction | |||
| Supercritical fluid | substance at a temperature and pressure higher than its critical point; exhibits properties intermediate between those of gaseous and liquid states | |||
| Surroundings | all matter other than the system being studied | |||
| Symbolic realm | specialized language used to represent components of the macroscopic and microscopic domains, such as chemical symbols, chemical formulas, chemical equations, graphs, drawings, and calculations | |||
| System | portion of matter undergoing a chemical or physical change being studied | |||
| intensive property of matter that is a quantitative measure of “hotness” and “coldness” | ||||
| Termolecular elementary reaction | rare reaction that involves three reactant particles colliding simultaneously | |||
| Tetrahedral geometry | shape in which four outside groups are placed around a central atom such that a three-dimensional shape is generated with four corners and 109.5° angles between each pair and the central atom | |||
| Theoretical yield | amount of product that may be produced from a given amount of reactant(s) according to the reaction stoichiometry | |||
| Thermal energy | kinetic energy associated with the random motion of atoms and molecules | |||
| Thermochemistry | study of measuring the amount of heat energy absorbed or released during a chemical reaction or a physical change | |||
| Thermodynamics | the study of energy and its transformations | |||
| Third law of thermodynamics | entropy of a perfect crystal at absolute zero (0 K) is zero | |||
| Threshold frequency | frequency of light shone at a metal below which no electrons are ejected and above which the number of ejected electrons is proportional to light intensity | |||
| Torr | unit of pressure; 1 torr = 1/760 atm | |||
| Total pressure | the sum of the pressures that each gas in a mixture would exert if it were alone in the container | |||
| Transition metal | element in groups 3–11 | |||
| Transition state | high-energy intermediate in which bonds are partially broken and formed | |||
| Trigonal bipyramidal geometry | shape in which five outside groups are placed around a central atom such that three form a flat triangle with 120° angles between each pair and the central atom, and the other two form the apex of two pyramids, one above and one below the triangular plane | |||
| Trigonal planar geometry | shape in which three outside groups are placed in a flat triangle around a central atom with 120° angles between each pair and the central atom | |||
| Triple bond | bond in which three pairs of electrons are shared between two atoms | |||
| Triple point | temperature and pressure at which the vapor, liquid, and solid phases of a substance are in equilibrium | |||
| Unimolecular elementary reaction | reaction that involves the rearrangement or decomposition of a single reactant molecule | |||
| Unit conversation factor | ratio of equivalent quantities expressed with different units; used to convert from one unit to a different unit | |||
| Valence electron | electron in the outermost or valence shell (highest value of n) of a ground-state atom; determines how an element reacts | |||
| Valence Shell Electron-Shell Repulsion theory (VSEPR) | theory used to predict the bond angles in a molecule based on positioning regions of high electron density as far apart as possible to minimize electrostatic repulsion | |||
| Vapor pressure | pressure exerted by a vapor in equilibrium with a solid or a liquid at a given temperature | |||
| Vaporization | change from liquid state to gaseous state | |||
| Voltage | a measure of the electrical potential difference between the two electrodes, indicating how much energy per unit charge can be obtained from a redox reaction | |||
| Voltmeter | instrument that measures electrical potential difference (voltage) between two electrodes in an electrochemical cell | |||
| amount of space occupied by an object | ||||
| Wave | oscillation that can transport energy from one point to another in space | |||
| Wave-particle duality | term used to describe the fact that elementary particles including matter exhibit properties of both particles (including localized position, momentum) and waves (including nonlocalization, wavelength, frequency) | |||
| Wavefunction (ψ) | mathematical description of an atomic orbital that describes the shape of the orbital; it can be used to calculate the probability of finding the electron at any given location in the orbital, as well as dynamical variables such as the energy and the angular momentum | |||
| Wavelength (λ) | distance between two consecutive peaks or troughs in a wave | |||
| Work (w) | energy transfer due to changes in external, macroscopic variables such as pressure and volume; or causing matter to move against an opposing force |