A covalent bond between atoms with different electronegativities in which electron density is
unevenly distributed, giving the bond positive and negative ends.
Polar molecule
A molecule possessing one or more polar covalent bond(s) and a geometry that allows the bond
dipole moments to add up to a net dipole moment, e.g., H 2 O.
Polyprotic acid
An acid capable of donating more than one proton, e.g., H 2 CO 3.
Positron
An “antielectron”: It has the same mass but opposite charge as an electron, and is emitted during a
particular form of radioactive decay.
Potential energy diagram
An energy diagram that relates the potential energy of the reactants and products of a reaction to
details of the reaction pathway. By convention, the x axis shows the progression of the reaction, and
the y axis shows potential energy.
Precipitate
An insoluble solid that separates from a solution, generally the result of mixing two or more
solutions or of a temperature change.
Pressure
Average force per unit area measured in atmospheres, torr (mm Hg), or pascals (Pa). 1 atm = 760 torr
= 760 mm Hg = 1.01 × 10^2 kPa.
Primary structure
The amino acid sequence of a protein.