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The time required for half of a reactant to be converted into product(s). The time required for half of a given sample to undergo radioactive decay.

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Resonance

The concept in which two or more equivalent dot formulas for the same arrangement of atoms (resonance structures) are necessary to describe the bonding in a molecule or ion.

Atomic Number


Integral number of protons in the nucleus, defines the identity of element.
 

Phase Diagram

Diagram that shows equilibrium temperature-pressure relationships for different phases of a substance.

Ground State

The lowest energy state or most stable state of an atom, molecule or ion.

Sigma Orbital

Molecular orbital resulting from head-on overlap of two atomic orbitals.

Law of Definite Proportions (Law of Constant Composition)

The law stating that a pure substance will always have the same percent by weight. Different samples of a pure compound always contain the same elements in the same proportions by mass.

Corrosion

Oxidation of metals in the presence of air and moisture.

Square Planar

A term used to describe molecules and polyatomic ions that have one atom in the center and four atoms at the corners of a square.

Periodicity

Regular periodic variations of properties of elements with atomic number (and position in the periodic table).

Transition State Theory

Theory of reaction rates that states that reactants pass through high-energy transition states before forming products.

Coordination Sphere

The metal ion and its coordinating ligands but not any uncoordinated counter-ions.

xenon tetrafluoride

A colorless, crystalline compound, XeF4, prepared by heating a gaseous mixture of fluorine and xenon.

Equilibrium or Chemical Equilibrium

A state of dynamic balance in which the rates of forward and reverse reactions are equal, the state of a system when neither forward or reverse reaction is thermodynamically favored.

Leclanche Cell

A common type of dry cell.

Dipole-dipole Interactions

Attractive interactions between polar molecules, that is, between molecules with permanent dipoles.

Saponification

Hydrolysis of esters in the presence of strong soluable bases.

Cation

A positive ion, an atom or group of atoms that has lost one or more electrons.

DP number

The degree of polymerization, the average number of monomer units per polymer unit.

Autoionization

An ionization reaction between identical molecules.

Crystal Field Theory

Theory of bonding in transition metal complexes in which ligands and metal ions are treated as point charges, a purely ionic model, ligand point charges represent the crystal (electrical) field perturbing the metal?s d orbitals containing nonbonding electrons.