Gen Chem II Final

antibonding MO

A molecular orbital formed when wave functions are subtracted from each other, which decreases electron density between the nuclei and leaves a node. Electrons occupying such an orbital destabilize the molecule.

bonding MO

A molecular orbital formed when wave functions are added to each other, which increases electron density between the nuclei. Electrons occupying such an orbital stabilize the molecule.

homonuclear diatomic molecule

A molecule composed of two identical atoms.

hybrid orbital

An atomic orbital postulated to form during bonding by the mathematical mixing of specific combinations of nonequivalent orbitals in a given atom.

hybridization

A postulated process of orbital mixing to form hybrid orbitals.

MO bond order

One-half the difference between the number of electrons in bonding MOs and the number in antibonding MOs.

molecular orbital (MO)

An orbital of given energy and shape that extends over a molecule and can be occupied by no more than two paired electrons.

molecular orbital (MO) diagram

A depiction of the relative energy and number of electrons in each MO, as well as the atomic orbitals from which the MOs form.

molecular orbital (MO) theory

A model that describes a molecule as a collection of nuclei and electrons in which the electrons occupy orbitals that extend over the entire molecule.

nonbonding MO

A molecular orbital that is not involved in bonding.

pi (π) bond

A covalent bond formed by sideways overlap of two atomic orbitals that has two regions of electron density, one above and one below the internuclear axis.

pi (π) MO

A molecular orbital formed by combination of two atomic (usually p) orbitals whose orientations are perpendicular to the internuclear axis.

sigma (σ) bond

A type of covalent bond that arises through end-to-end orbital overlap and has most of its electron density along an imaginary line joining the nuclei.

sigma (σ) MO

A molecular orbital that is cylindrically symmetrical about an imaginary line that runs through the nuclei of the component atoms.

sp hybrid orbital

An orbital formed by the mixing of one s and one p orbital of a central atom.

sp2 hybrid orbital

An orbital formed by the mixing of one s and two p orbitals of a central atom.

sp3 hybrid orbital

An orbital formed by the mixing of one s and three p orbitals of a central atom.

sp3d hybrid orbital

An orbital formed by the mixing of one s, three p, and one d orbital of a central atom.

sp3d2 hybrid orbital

An orbital formed by the mixing of one s, three p, and two d orbitals of a central atom.

valence bond (VB) theory

A model that attempts to reconcile the shapes of molecules with those of atomic orbitals through the concepts of orbital overlap and hybridization.

alloy

A mixture with metallic properties that consists of solid phases of two or more pure elements, a solid-solid solution, or distinct intermediate phases.

boiling point elevation (ΔTb)

The increase in the boiling point of a solvent caused by the presence of dissolved solute.

charge density

The ratio of the charge of an ion to its volume.

colligative property

A property of a solution that depends on the number, not the identity, of solute particles. (See also boiling point elevation, freezing point depression, osmotic pressure, and vapor pressure lowering.)

colloid

A heterogeneous mixture in which a dispersed (solute-like) substance is distributed throughout a dispersive (solvent-like) substance.

desalination

A process used to remove large amounts of ions from seawater, usually by reverse osmosis.

dipole-induced dipole force

The intermolecular attraction between a polar molecule and the oppositely charged pole it induces in a nearby molecule.

entropy (S)

A thermodynamic quantity related to the number of ways the energy of a system can be dispersed through the motions of its particles.

fractional distillation

A physical process involving numerous vaporization-condensation steps used to separate two or more volatile components.

freezing point depression (ΔTf)

The lowering of the freezing point of a solvent caused by the presence of dissolved solute particles.

hard water

Water that contains large amounts of divalent cations, especially Ca2+ and Mg2+.

heat of hydration (ΔHhydr)

(also enthalpy of hydration) The enthalpy change occurring when 1 mol of a gaseous species (often an ion) is hydrated. The sum of the enthalpies from separating water molecules and mixing the gaseous species with them; designated ΔHhydr at the standard state.

heat of solution (ΔHsoln)

(also enthalpy of solution) The enthalpy change occurring when a solution forms from solute and solvent. The sum of the enthalpies from separating solute and solvent substances and mixing them; designated ΔHsoln at the standard state.

Henry’s law

A law stating that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid: Sgas = kH × Pgas.

hydration

Solvation in water.

hydration shell

The oriented cluster of water molecules that surrounds an ion in aqueous solution.

ideal solution

A solution that follows Raoult's law at any concentration.

immiscible

Insoluble; usually applied to liquids that do not dissolve in each other.

ion exchange

A process of softening water by exchanging one type of ion (usually Ca2+) for another (usually Na+) by binding the ions on a specially designed resin.

ionic atmosphere

A cluster of ions of net opposite charge surrounding a given ion in solution.

ion-induced dipole force

The attractive force between an ion and the dipole it induces in the electron cloud of a nearby nonpolar molecule.

like-dissolves-like rule

An empirical observation stating that substances having similar kinds of intermolecular forces dissolve in each other.

mass percent [% (w/w)]

(also mass % or percent by mass) The fraction by mass expressed as a percentage. A concentration term expressed as the mass of solute dissolved in 100. parts by mass of solution.

miscible

Soluble in any proportion.

molality (m)

A concentration term expressed as number of moles of solute dissolved in 1000 g (1 kg) of solvent.

mole fraction (X)

A concentration term expressed as the ratio of number of moles of solute to the total number of moles (solute plus solvent).

nonelectrolyte

A substance whose aqueous solution does not conduct an electric current.

osmosis

The process by which solvent flows through a semipermeable membrane from a dilute to a concentrated solution.

osmotic pressure (π)

The pressure that results from the ability of solvent, but not solute, particles to cross a semipermeable membrane. The pressure required to prevent the net movement of solvent across the membrane.

Raoult’s law

A law stating that the vapor pressure of solvent above a solution equals the mole fraction of solvent times the vapor pressure of pure solvent: Psolvent = Xsolvent * P^o solvent.

reverse osmosis

A process for preparing drinkable water that uses an applied pressure greater than the osmotic pressure to remove ions from an aqueous solution, typically seawater.

saturated solution

A solution that contains the maximum amount of dissolved solute at a given temperature (prepared with undissolved solute present).

semipermeable membrane

A membrane that allows solvent, but not solute, to pass through.

soap

The salt formed in a reaction between a fatty acid and a strong base, usually a Group 1A(1) or 2A(2) hydroxide.

solubility (S)

The maximum amount of solute that dissolves in a fixed quantity of a particular solvent at a specified temperature.

solute

The substance that dissolves in the solvent.

solvation

The process of surrounding a solute particle with solvent particles.

solvent

The substance in which one or more solutes dissolve.

strong electrolyte

A substance that is a good conductor of electric current in solution because it dissociates or ionizes completely.

supersaturated solution

An unstable solution in which more solute is dissolved than in a saturated solution.

suspension

A heterogeneous mixture containing particles that are visibly distinct from the surrounding fluid.

Tyndall effect

The scattering of light by a colloid.

unsaturated solution

A solution in which more solute can be dissolved at a given temperature.

vapor pressure lowering (ΔP)

The lowering of the vapor pressure of a solvent caused by the presence of dissolved solute particles.

volume percent [% (v/v)]

A concentration term defined as the volume of solute in 100. volumes of solution.

wastewater

Used water, usually containing industrial and/or residential waste, that is treated before being returned to the environment.

water softening

The process of replacing the hard-water ions Ca2+ and Mg2+ with Na+ ions.

weak electrolyte

A substance that is a poor conductor of electric current in solution because it only partially dissociates or ionizes.

average rate

The change in concentration of reactants (or products) divided by a finite time period.

initial rate

The instantaneous rate at the moment the reactants are mixed, that is, at t = 0.

collision theory

A model that explains reaction rate as based on the number, energy, and orientation of colliding particles.

instantaneous rate

The reaction rate at a particular time, given by the slope of a tangent to a plot of reactant concentration vs. time.

rate constant (k)

The proportionality constant that relates reaction rate to reactant (and product) concentrations.

rate law

(also rate equation) An equation that expresses the rate of a reaction as a function of reactant (and product) concentrations and temperature.

reaction rate

The change in the concentrations of reactants (or products) with time.

activation energy (Ea)

The minimum energy with which molecules must collide to react.

catalyst

A substance or mixture that increases the rate of a reaction without being used up in the process.

Arrhenius equation

An equation that expresses the exponential relationship between temperature and the rate constant

average rate

The change in concentration of reactants (or products) divided by a finite time period.

bimolecular reaction

An elementary reaction involving the collision of two reactant species.

chemical kinetics

The study of the rates of reactions and the factors that affect them.

effective collision

A collision in which the particles meet with sufficient energy and an orientation that allows them to react.

collision theory

A model that explains reaction rate as based on the number, energy, and orientation of colliding particles.

elementary reaction

(also elementary step) A simple reaction that describes a single molecular event in a proposed reaction mechanism.

enzyme

A biological macromolecule (usually a protein) that acts as a catalyst.

enzyme-substrate complex (ES)

The intermediate in an enzyme-catalyzed reaction, which consists of enzyme and substrate(s) and whose concentration determines the rate of product formation.

frequency factor (A)

The product of the collision frequency Z and an orientation probability factor p that is specific for a reaction.

half-life (t1/2)

In chemical processes, the time required for the reactant concentration to reach half of its initial value. In nuclear processes, the time required for half the initial number of nuclei in a sample to decay.

heterogeneous catalyst

A catalyst that occurs in a different phase from the reactants, usually a solid interacting with gaseous or liquid reactants.

homogeneous catalyst

A catalyst (gas, liquid, or soluble solid) that exists in the same phase as the reactants.

hydrogenation

The addition of hydrogen to a carbon-carbon multiple bond to form a carbon-carbon single bond.

induced-fit model

A model of enzyme action that pictures the binding of the substrate as inducing the active site to change its shape and become catalytically active.

instantaneous rate

The reaction rate at a particular time, given by the slope of a tangent to a plot of reactant concentration vs. time.

integrated rate law

A mathematical expression for reactant concentration as a function of time.

lock-and-key model

A model of enzyme function that pictures the enzyme active site and the substrate as rigid shapes that fit together as a lock and key, respectively.

molecularity

The number of reactant particles involved in an elementary step.

rate-determining step

(also rate-limiting step) The slowest step in a reaction mechanism and therefore the step that limits the overall rate.

rate law

(also rate equation) An equation that expresses the rate of a reaction as a function of reactant (and product) concentrations and temperature.

reaction energy diagram

A graph that shows the potential energy of a reacting system as it progresses from reactants to products.

reaction intermediate

A substance that is formed and used up during the overall reaction and therefore does not appear in the overall equation.