5) General Chemistry

Absolute zero

The temperature at which all substances have no thermal energy; 0 K or -273.15°C.

Absorption spectrum

The series of discrete lines at characteristic frequencies representing the energy required to excite an electron from the ground state.

Acid

A species that donates hydrogen ions or accepts electrons.

Acid dissociation constant (Ka)

The equilibrium constant that measures the degree of dissociation of an acid under specific conditions.

Acidic solution

An aqueous solution that contains more H+ ions than OH- ions; pH < 7 under standard conditions.

Actinide series

The series of chemical elements atomic numbered 89-103 and falling between the s and d blocks on the periodic table.

Activation energy (Ea)

The minimum amount of energy required for a reaction to reach the transition state; also called energy barrier.

Actual yield

The experimental quantity of a substance obtained at the end of a reaction.

Adiabatic process

A process that occurs without the transfer of heat into or out of the system.

Alkali metals

Elements found in Group IA of the periodic table; highly reactive, readily losing one valence electron to form ionic compounds with nonmetals.

Alkaline earth metals

Elements found in Group IIA of the periodic table; chemistry is similar to that of the alkali metals, except that they have two valence electrons and, thus, form +2 cations.

Amphiprotic species

A species that may either gain or lose a proton.

Amphoteric species

A species capable of reacting as either an acid or base, depending on the nature of the reactants.

Angular momentum

The rotational analog of linear momentum.

Anion

An ionic species with a negative charge.

Anode

The electrode at which oxidation occurs.

Antibonding orbital

A molecular orbital formed by the overlap of two or more atomic orbitals; energy is greater than the energy of the combining atomic orbitals.

Aqueous solution

A solution in which water is the solvent.

Arrhenius acid

A species that donates protons (H+) in aqueous solution.

Arrhenius base

A species that donates hydroxide ions (OH-) in aqueous solution.

Arrhenius equation

A chemical kinetics equation that relates the rate constant (k) of a reaction with the frequency factor (A), the activation energy (Ea), the ideal gas constant (R), and temperature (T) in kelvin.

Atom

The smallest unit of an element that retains the properties of the element; it cannot be further broken down by chemical means.

Atomic mass

The mass of a given isotope of an element; closely related to the mass number.

Atomic mass unit (amu)

A unit of mass defined as 1/12

the mass of a carbon-12 atom; approximately equal to the mass of one proton or one neutron.

Atomic number

The number of protons in a given element.

Atomic orbital

Describes the region of space where there is a high probability of finding an electron.

Atomic radius

The average distance between a nucleus and its outermost electron; usually measured as one-half the distance between two nuclei of an element in its elemental form.

Atomic weight

The weighted average mass of the atoms of an element, taking into account the relative abundance of all naturally occurring isotopes.

Aufbau principle

The concept that electrons fill energy levels in order of increasing energy, completely filling one sublevel before beginning to fill the next.

Autoionization

The process by which a molecule (usually water) spontaneously dissociates into cations and anions.

Avogadro's number

The number of atoms or molecules in one mole of a substance: 6.02 × 1023 mol-1.

Avogadro's principle

The law stating that under the same conditions of temperature and pressure, equal volumes of different gases will have the same number of molecules.

Azimuthal quantum number (l)

The quantum number denoting the sublevel or subshell in which an electron can be found; reveals the shape of the orbital.

Balanced equation

An equation for a chemical reaction in which the number of atoms for each element in the reaction and the total charge are the same for the reactants and the products.

Balmer series

Part of the emission spectrum for hydrogen, representing transitions of an electron from energy levels n \> 2 to n \= 2.

Barometer

A tool for measuring pressure.

Base

A species that donates hydroxide ions or electron pairs or that accepts protons.

Base dissociation constant (Kb)

The equilibrium constant that measures the degree of dissociation for a base under specific conditions.

Basic solution

An aqueous solution that contains more OH- ions than H+ ion; pH \> 7 under standard conditions.

Bohr model

The model of the hydrogen atom in which electrons assume certain circular orbits around a positive nucleus.

Boiling point

The temperature at which the vapor pressure of a liquid is equal to the incident pressure; the normal boiling point of any liquid is defined as its boiling point at a pressure of 1 atmosphere.

Boiling point elevation

The amount by which a given quantity of solute raises the boiling point of a liquid; a colligative property.

Bond energy

The energy (enthalpy change) required to break a particular bond under given conditions.

Bond enthalpy

The average energy that is required to break a particular type of bond between atoms in the gas phase.

Bonding electrons

Electrons located in the valence shell of an atom and involved in a covalent bond.

Bonding orbital

A molecular orbital formed by the overlap of two or more atomic orbitals; energy is less than that of the combining orbitals.

Bond length

The average distance between two nuclei in a bond; as the number of shared electron pairs increases, the bond length decreases.

Bond order

The number of shared electron pairs between two atoms; a single bond has a bond order of 1, a double bond has a bond order of 2, a triple bond has a bond order of 3.

Boyle's law

The law stating that at constant temperature, the volume of a gaseous sample is inversely proportional to its pressure.

Broken-order reaction

A reaction with noninteger orders in its rate law.

Brønsted

Lowry acid-A proton donor.

Brønsted

Lowry base-A proton acceptor.

Buffer

A solution containing a weak acid and its salt (or a weak base and its salt) that tends to resist changes in pH.

Buffer region

The portion of a titration curve in which the concentration of an acid is approximately equal to that of its conjugate base; pH remains relatively constant through this region.

Buffering capacity

The degree to which a system can resist changes in pH.

Calorie (cal)

A unit of thermal energy.

Calorimeter

An apparatus used to measure the heat absorbed or released by a reaction.

Catalyst

A substance that increases the rates of the forward and reverse directions of a specific reaction by lowering activation energy, but is itself left unchanged.

Cathode

The electrode at which reduction takes place.

Cation

An ionic species with a positive charge.

Celsius (°C)

A temperature scale defined by having 0°C equal to the freezing point of water and 100°C equal to the boiling point of water; otherwise known as the centigrade temperature scale.

Chalcogens

Elements found in Group VIA of the periodic table with diverse chemistry; the group contains metals, nonmetals (like oxygen), and metalloids; typically form -2 anions.

Charging

A state of an electrochemical cell in which an external electromotive force is being used to return a cell to its original state; during this process, electrons are transferred nonspontaneously from cathode to anode.

Charles's law

The law stating that the volume of a gas at constant pressure is directly proportional to its absolute (kelvin) temperature.

Chelation

The process of binding metal ions to the same ligand at multiple points.

Chemical bond

The interaction between two atoms resulting from the sharing or transfer of electrons.

Chemical equation

An expression used to describe the quantity and identity of the reactants and products of a reaction.

Chemical properties

Those properties of a substance related to the chemical changes that it undergoes, such as ionization energy and electronegativity.

Closed system

A system that can exchange energy but not matter with its surroundings.

Colligative properties

Those properties of solutions that depend only on the number of solute particles present but not on the nature of those particles.

Collision theory of chemical kinetics

A theory that states that the rate of a reaction is proportional to the number of collisions per second between reacting molecules that have sufficient energy to overcome the activation energy barrier; implies that only a fraction of collisions are sufficient.

Combination reaction

A reaction in which two or more reactants form a single product.

Combined gas law

A gas law that combines Boyle's law, Charles's law, and Gay-Lussac's law to state that pressure and volume are inversely proportional to each other, and each is directly proportional to temperature.

Combustion reaction

A reaction in which an oxidant (typically oxygen) reacts with a fuel (typically a hydrocarbon) to yield water and an oxide (such as carbon dioxide if between a hydrocarbon and oxygen).

Common ion effect

A shift in the equilibrium of a solution due to the addition of ions of a species already present in the reaction mixture.

Complexation reaction

A reaction in which a central cation is bound to one or more ligands.

Complex ion

A polyatomic molecule in which a central cation is bonded to electron pair donors called ligands.

Compound

A pure substance that can be decomposed to produce elements, other compounds, or both.

Compression

Reduction in the volume of a gas.

Concentrated solution

A solution with a high concentration value; the cutoff for the term "concentrated" depends on the purpose and identity of the solution.

Concentration

The amount of solute per unit of solvent or the relative amount of one component in a mixture.

Concentration cell

A cell that creates an electromotive force (emf or voltage) using a single chemical species in half-cells of varying concentration.

Condensation

The process in which a gas transitions to the liquid state.

Conductor

A material in which electrons are able to transfer energy in the form of heat or electricity.

Conjugate acid

base pair-The relationship between a Brønsted-Lowry acid and its deprotonated form, or a Brønsted-Lowry base and its protonated form.

Coordinate covalent bond

A covalent bond in which both electrons of the bonding pair are donated by one of the bonded atoms.

Coordination number

The number of atoms that are bound to a central atom.

Covalent bond

A chemical bond formed by the sharing of an electron pair between two atoms; can be in the form of single bonds, double bonds, or triple bonds.

Critical point

The point in a phase diagram beyond which the phase boundary between liquid and gas no longer exists.

Critical pressure

The vapor pressure at the critical temperature of a given substance.

Critical temperature

Also known as the critical point. The highest temperature at which the liquid and gas phases of a substance can coexist; above this temperature, the liquid and gas phases are indistinguishable.

Crystal

A solid in which atoms, ions, or molecules are arranged in a regular, three-dimensional lattice structure.

d subshell

Subshell corresponding to the angular momentum quantum number l \= 2; contains five orbitals and is found in the third and higher principal energy levels.

Dalton's law of partial pressures

The law stating that the sum of the partial pressures of the components of a gaseous mixture must equal the total pressure of the sample.

Daniell cell

An electrochemical cell in which the anode is the site of Zn metal oxidation and the cathode is the site of Cu2+ ion reduction.

Decomposition reaction

A reaction in which a single compound breaks down into two or more products.

Delocalized orbitals

Molecular orbitals in which electron density is spread over an entire molecule, or a portion thereof, rather than being localized between two atoms.

Density (ρ)

A physical property of a substance, defined as the mass contained in a unit of volume.

Deposition

In most chemical processes, the direct transition of a substance from the gaseous state to the solid state; in electrochemical reactions, the buildup of a solid precipitate onto an electrode.