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P
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- p block
- Columns 13 through 18 of the periodic table, containing elements in the periodic table over which the p atomic orbitals are being filled.
- para
- Describing the relationship between two groups attached to carbon atoms on a benzene-like ring that have two carbon atoms between them.
- paramagnetic
- Describing a substance containing unpaired electrons that is attracted by a magnetic field.
- partial pressure
- That portion of the total pressure of a mixture of gases contributed by the presence of one of the component gases.
- pascal
- The SI unit for pressure, equal to a kg/s2m
- Pauli exclusion principle
- The statement that no two electrons in an atom can have the same set of quantum numbers; the principle leads to the rule that only two electrons (having opposite spin) can occupy an atomic orbital.
- peptide
- A molecule of two or more amino acids joined by amide linkages or "peptide bonds."
- peptide bond
- The amide linkage that joins the carboxylic acid end of one amino acid with the amino end of another amino acid to form a peptide or protein.
- percent ionization
- The fraction (expressed as a percent) of an electrolyte that dissociates into ions; this fraction depends upon both the value of the equilibrium constant and the concentration of the species that is dissociating.
- period
- Those elements from a single column of the periodic table.
- periodic table
- A chart showing the symbols of the elements arranged in order by atomic number and having chemically related elements appearing in columns.
- pH
- A logarithmic measure of the concentration of hydrogen ion expressed as -log10([H+]).
- phase diagram
- A diagram showing conditions, most typically of pressure and temperature, under which different phases of a substance exist at equilibrium.
- photon
- A quantum of energy from electromagnetic radiation; the value of the energy available is the product of the frequency of light and Planck's constant.
- phototube detector
- The phototube detector converts light energy to an electrical signal. The intensity of light can be measured with the phototube detector.
- physical change
- A process in which the identity of substances remains unchanged.
- physical property
- A characteristic of a material that can be measured without changing the material's chemical composition.
- pi bond
- A bond in which the electron density lies above and below a plane containing the bonded atoms; formed by the overlap of two p orbitals or a p orbital and a d orbital.
- pK
- A logarithmic measure of the value of the equilibrium constant expressed as -log10([K]).
- Planck's constant
- A proportionality constant between the energy of a photon of light and the frequency of that light; equal to 6.6261 x 10-34 J sec
- pOH
- A logarithmic measure of the concentration of hydroxide ion expressed as -log10([OH-]).
- polar
- Describing a molecule having a separation of centers of positive and negative electrical charge that makes the molecule assume certain orientations more than others in an electric field.
- polarizability
- The ability of the electrons in a species to change position in response to the presence of an outside electrical field.
- pollution
- The contamination of the air, water, and earth by personal, industrial, and farm waste.
- polyatomic
- Containing two or more atoms.
- polymer
- A large molecule containing a large number of repeating units; a substance formed from such molecules.
- polymerization
- The process of forming a polymer from monomers.
- polymorphism
- The ability of a substance to exist in more than one crystalline form.
- polypeptide
- A polymer of many amino acids joined by amide linkages or "peptide bonds."
- polyprotic
- Describing an acid that can donate two or more hydrogen ions ("protons") to a base.
- polysaccharide
- A polymer of many units, each of which is a carbohydrate.
- positional isomer
- One of two or more compounds that have the same chemical composition but that differ in the location at which functional groups are attached to the backbone of atoms.
- positron
- A positively charged particle having the same mass as an electron.
- potentiometer
- An instrument for measuring the voltage of a system by opposing that voltage until no current flows.
- precipitation
- The formation of a solid within a solution, often by the combination of cations and anions to form an insoluble ionic compound.
- precision
- The extent of agreement among several experimental values.
- pressure
- Force per unit area; in gases arising from the effect of collisions by the molecules of the gas with the wall of the container.
- primary structure
- The sequence of amino acids that defines a protein.
- product
- A substance produced by a chemical reaction.
- protein
- A biological polymer of amino acids joined by peptide bonds.
- proton
- The positively charged particle in an atomic nucleus; its mass is similar to the mass of a hydrogen atom.
- pseudo-first-order reaction
- A reaction in which the concentrations of reactants are such that the reaction appears to depend directly upon the concentration of one reactant; the concentrations of other reactants change so little as to affect the rate only negligibly.
- pyrophoric
- Igniting spontaneously when exposed to air.
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