Glossary

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 (K_a) | equilibrium constant for the ionization of a weak acid

Acid-base indicator | organic acid or base whose color changes depending on the pH of the solution it is in

Acidic | describes a solution in which [H3O⁺]>[OH⁻]

Alcohol | organic compound with a hydroxyl group (–OH) bonded to a carbon atom

Alkane | molecule consisting of only carbon and hydrogen atoms connected by single (σ) bonds

Alkene | molecule consisting of carbon and hydrogen containing at least one carbon-carbon double bond

Alkyl group | substituent, consisting of an alkane missing one hydrogen atom, attached to a larger structure

Alkyne | molecule consisting of carbon and hydrogen containing at least one carbon-carbon triple bond

Amonton’s Law | when the volume of a gas is held constant, increasing the temperature of the gas increases its pressure

Anion | negatively charged atom or molecule (contains more electrons than protons)

Anode | 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

Aqueous solution | solution for which water is the solvent, noted as physical state (aq)

Atmosphere (atm) | unit of pressure; 1 atm = 101,325 Pa

Atomic number (Z) | number of protons in the nucleus of an atom

Atomic orbital | mathematical function that describes the behavior of an electron in an atom (also called the wavefunction), it can be used to find the probability of locating an electron in a specific region around the nucleus, as well as other dynamical variables

Atomic radius | the total distance from an atom’s nucleus to the outermost orbital of electron

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

Azide ion | N^3-

Balanced equation | chemical equation with equal numbers of atoms for each element in the reactant and product

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 (K_b) | equilibrium constant for the ionization of a weak base

Basic | describes a solution in which [H3O⁺] < [OH⁻]

Bohr’s model of the hydrogen atom | structural model in which an electron moves around the nucleus only in circular orbits, each with a specific allowed radius; the orbiting electron does not normally emit electromagnetic radiation, but does so when changing from one orbit to another.

Boiling point | temperature at which the vapor pressure of a liquid equals the pressure of the gas above it

Bond angle | angle between any two covalent bonds that share a common atom 

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 | (also, bond length) distance between the nuclei of two bonded atoms

Bond energy | (also, bond dissociation energy) energy required to break a covalent bond in a gaseous substance

Bond length | distance between the nuclei of two bonded atoms at which the lowest potential energy is achieved

Brønsted-Lowry acid | proton donor

Brønsted-Lowry base | proton acceptor

Cathode | 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

Cation | positively charged atom or molecule (contains fewer electrons than protons)

Central atom | atom to which one or more atoms or groups is attached through covalent bonds

Chair confirmation | A three-dimensional conformation of cyclohexane that resembles the rough shape of a chair. The chair form of cyclohexane is the lowest-energy conformation of the molecule

Chiral | Chiral molecules are those that do not have a plane of symmetry and are therefore not superimposable on their mirror image.  Mirror image non-superimposable molecules.

cis configuration | configuration of a geometrical isomer in which two similar groups are on the same side of an imaginary reference line on the molecule

Concentration | quantitative measure of the relative amounts of solute and solvent present in a solution

Conjugate acid | substance formed when a base gains a proton

Conjugate base | substance formed when an acid loses a proton

Covalent bond | bond formed when electrons are shared between atoms

Covalent compound | (also, molecular 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 atoms when they are joined by a covalent bond

Cycloalkane | An alkane that contains a ring of carbons

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

Diaxial | A pair of atoms or groups that are both in an axial position on a cyclohexane ring

Dimensional analysis | (also, factor-label method) versatile mathematical approach that can be applied to computations ranging from simple unit conversions to more complex, multi-step calculations involving several different quantities

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 | (also, London dispersion force) attraction between two rapidly fluctuating, temporary dipoles; significant only when particles are very close together

Dissolved | describes 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

Effective nuclear charge (Z_eff) | charge that leads to the Coulomb force exerted by the nucleus on an electron, calculated as the nuclear charge minus shielding

Electrical potential | energy per charge; in electrochemical systems, it depends on the way the charges are distributed within the system; the SI unit of electrical potential is the volt (1V=1JC)

Electron | negatively charged, subatomic particle of relatively low mass located outside the nucleus

Electron domain | the region in which electrons are most likely to be found

Electron-pair geometry or Electron domain geometry | arrangement around a central atom of all regions of electron density (bonds, lone pairs, or unpaired electrons)

Electronegativity | tendency of an atom to attract electrons in a bond to itself

Element | substance that is composed of a single type of atom; a substance that cannot be decomposed by a chemical change

Endothermic process | chemical reaction or physical change that absorbs heat

Energy | 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

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 | 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

Equilibrium constant (K) | value of the reaction quotient for a system at equilibrium

Excited state | state having an energy greater than the ground-state energy

Exothermic process | chemical reaction or physical change that releases heat

Group | vertical column of the periodic table

Heat (q) | transfer of thermal energy between two bodies

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

Hybridization | model that describes the changes in the atomic orbitals of an atom when it forms a covalent compound

Hybrid orbital | orbital created by combining atomic orbitals on a central atom

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

Hydroxide | compound of a metal with the hydroxide ion OH⁻ or the group −OH

Ideal gas | a gas whose molecules do not interact and do not take up space

Intermolecular force | noncovalent attractive force between atoms, molecules, and/or ions

Ion | electrically charged atom or molecule (contains unequal numbers of protons and electrons)

Ion-dipole attraction | electrostatic attraction between an ion and a polar molecule

Ion-product constant for water (K_w) | equilibrium constant for the autoionization of water

Ionic bond | electrostatic forces of attraction between the oppositely charged ions of an ionic compound

Ionic compound | compound composed of cations and anions combined in ratios, yielding an electrically neutral substance

Isomers | compounds with the same chemical formula but different structures

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

K_c | equilibrium constant for reactions based on concentrations of reactants and products

Kelvin (K) | SI unit of temperature; 273.15 K = 0 ºC

Kinetic energy | energy of a moving body, in joules, equal to [latex]\dfrac{1}{2}mv^2[/latex] (where m = mass and v = velocity)

K_P | equilibrium constant for gas-phase reactions based on partial pressures of reactants and products

K_sp (Solubility product)  | equilibrium constant for the dissolution of a slightly soluble electrolyte

Le Chatelier’s principle | when a chemical system at equilibrium is disturbed, it returns to equilibrium by counteracting the disturbance

Lewis structure | diagram showing lone pairs and bonding pairs of electrons in a molecule or an ion

Lewis symbol | symbol for an element or monatomic ion that uses a dot to represent each valence electron in the element or ion

Line structure | an abbreviated drawing of a chemical structure which does not show all atoms, but uses lines to represent bonds and C atoms are implied at the corners of two lines

Linear | shape in which two outside groups are placed on opposite sides of a central atom

Liquid | state of matter that has a definite volume but indefinite shape

Liter (L) | (also, cubic decimeter) unit of volume; 1 L = 1,000 cm³

Lone pair | two (a pair of) valence electrons that are not used to form a covalent bond

Magnetic quantum number (m_l) | quantum number signifying the orientation of an atomic orbital around the nucleus; orbitals having different values of m_l 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

Melting point | temperature at which the solid and liquid phases of a substance are in equilibrium; see also freezing point

Metal | element that is shiny, malleable, good conductor of heat and electricity

Metal (representative) | atoms of the metallic elements of groups 1, 2, 12, 13, 14, 15, and 16, which form ionic compounds by losing electrons from their outer s or p orbitals to become positively charged

Molar mass | mass in grams of 1 mole of a substance

Molar solubility | solubility of a compound expressed in units of moles per liter (mol/L)

Molarity (M) | unit of concentration, defined as the number of moles of solute dissolved in 1 liter of solution

Mole | 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

Molecular compound | (also, covalent compound) composed of molecules formed by atoms of two or more different elements

Molecular equation | chemical equation in which all reactants and products are represented as neutral substances

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 | arrangement of atoms in a molecule or ion

Molecule | bonded collection of two or more atoms of the same or different elements

Neutral | describes a solution in which [H3O⁺] = [OH⁻]

Nonmetal | element that appears dull, poor conductor of heat and electricity, in an ionic compound the nonmetal has accepted electrons to become a negatively charged anion

Nonpolar | a molecule that does not have an overall partial charge

Octahedral | 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

Optical isomer | (also, enantiomer) molecule that is a nonsuperimposable mirror image with identical chemical and physical properties, except when it reacts with other optical isomers

Orbital diagram | pictorial representation of the electron configuration showing each orbital as a box and each electron as an arrow

Organic compound | natural or synthetic compound that contains carbon

Overlap | coexistence of orbitals from two different atoms sharing the same region of space, leading to the formation of a covalent bond

Oxidized  | the species that loses electrons in an oxidation reduction reaction is oxidized

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

Pauli exclusion principle | specifies that no two electrons in an atom can have the same value for all four quantum numbers

Period | (also, series) horizontal row of the periodic table

Periodic table | table of the elements that places elements with similar chemical properties close together

pH | logarithmic measure of the concentration of hydronium ions in a solution

Photon | smallest possible packet of electromagnetic radiation, a particle of light

Physical change | change in the state or properties of matter that does not involve a change in its chemical composition

Physical property | characteristic of matter that is not associated with any change in its chemical composition

Pi bond (π bond) | covalent bond formed by side-by-side overlap of atomic orbitals; the electron density is found on opposite sides of the internuclear axis

Polar covalent bond | covalent bond between atoms of different electronegativities; a covalent bond with a positive end and a negative end

Polar molecule | (also, dipole) molecule with an overall dipole moment

Polyatomic ion | ion composed of more than one atom

Pressure | force exerted per unit area

Principal quantum number (n) | quantum number specifying the shell an electron occupies in an atom

Quantum number | integer number having only specific allowed values and used to characterize the arrangement of electrons in an atom

R | A generalized abbreviation for an organic partial structure.

R configuration  | The configuration at a chirality center as specified using the Cahn–Ingold–Prelog sequence rules.

Rate expression | mathematical representation relating reaction rate to changes in amount, concentration, or pressure of reactant or product species per unit time

Rate of reaction or reaction rate | measure of the speed at which a chemical reaction takes place

Reactant | substance undergoing a chemical or physical change; shown on the left side of the arrow in a chemical equation

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

Reduced | the species which gains electrons in a oxidation reduction reaction is reduced

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

Rydberg’s Constant (R_H) | 2.18×10^-18 J

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

S configuration | the configuration at a chirality center as specified using the Cahn–Ingold–Prelog sequence rules.

Salt | an ionic compound consisting of a positively charged cation and a negatively charged anion

Shell | set of orbitals with the same principal quantum number, n

SI units (International System of Units) | standards fixed by international agreement in the International System of Units (Le Système International d’Unités)

Sigma bond (σ bond) | covalent bond formed by overlap of atomic orbitals along the internuclear axis

Significant figures | (also, significant digits) all of the measured digits in a determination, including the uncertain last digit

Single bond | bond in which a single pair of electrons is shared between two atoms

Solid | state of matter that is rigid, has a definite shape, and has a fairly constant volume

Solubility | extent to which a solute may be dissolved in water, or any solvent

Solubility product (K_sp) | equilibrium constant for the dissolution of a slightly soluble electrolyte

Soluble | a substance is able to be dissolved in a solvent

Solute | solution component present in a concentration less than that of the solvent

Solvation | exothermic process in which intermolecular attractive forces between the solute and solvent in a solution are established

Solvent | solution component present in a concentration that is higher relative to other components

sp hybrid orbital | one of a set of two orbitals with a linear arrangement that results from combining one s and one p orbital

sp² hybrid orbital | one of a set of three orbitals with a trigonal planar arrangement that results from combining one s and two p orbitals

sp³ hybrid orbital | one of a set of four orbitals with a tetrahedral arrangement that results from combining one s and three p orbitals

sp³d hybrid orbital | one of a set of five orbitals with a trigonal bipyramidal arrangement that results from combining one s, three p, and one d orbital

sp³d² hybrid orbital | one of a set of six orbitals with an octahedral arrangement that results from combining one s, three p, and two d orbitals

Spin quantum number (m_s) | number specifying the electron spin direction, either +1/2 or −1/2

Standard cell potential (E^o_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 reduction potential (E°) | the value of the reduction 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 | 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

State function | property depending only on the state of a system, and not the path taken to reach that state

Stereocenter | An alternative name for a chirality center

Stereochemistry | The branch of chemistry concerned with the three-dimensional arrangement of atoms in molecules

Stereoisomers | Isomers that have their atoms connected in the same order but have different three-dimensional arrangements. The term stereoisomer includes both enantiomers and diastereomers

Stoichiometry | relationships between the amounts of reactants and products of a chemical reaction

Stoichiometric coefficients | the numbers written in front of atoms, ions and molecules in a chemical reaction to balance the number of each element on both the reactant and product sides of the equation

Structural formula | shows the atoms in a molecule and how they are connected

Temperature | intensive property of matter that is a quantitative measure of “hotness” and “coldness”

Tetrahedral | 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

Thermochemical equation | a balanced stoichiometric equation that has reactants, products and the value of enthalpy change, DH

Thermochemistry | study of measuring the amount of heat absorbed or released during

Torr | unit of pressure; 1 torr=760 atm

trans configuration | configuration of a geometrical isomer in which two similar groups are on opposite sides of an imaginary reference line on the molecule

Trigonal bipyramidal | 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 | 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

Unit | standard of comparison for measurements

Unit conversion factor | ratio of equivalent quantities expressed with different units; used to convert from one unit to a different unit

Valence bond theory | description of bonding that involves atomic orbitals overlapping to form σ or π bonds, within which pairs of electrons are shared

Valence electrons | electrons in the outermost or valence shell (highest value of n) of a ground-state atom; determine how an element reacts

Valence shell | outermost shell of electrons in a ground-state atom; for main group elements, the orbitals with the highest n level (s and p subshells) are in the valence shell, while for transition

Valence shell electron-pair 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

Van der Waals force | attractive or repulsive force between molecules, including dipole-dipole, dipole-induced dipole, and London dispersion forces; does not include forces due to covalent or ionic bonding, or the attraction between ions and molecules

Volume | amount of space occupied by an object