Kaplan MCAT General Chemistry Review

Oxidation A reaction involving the net loss of electrons or, equivalently, an increase in oxidation number.

Oxidation number The number assigned to an atom in an ion or molecule that denotes its real or hypothetical charge. Atoms, alone or in molecules, of standard state elements have oxidation numbers of zero. Also called the oxidation state.

Oxidizing agent In a redox reaction, a species that gains electrons and is thereby reduced.

psubshell The subshells corresponding to the angular momentum quantum number l = 1, found in the second and higher principal energy levels. Each subshell contains three dumbbell-shaped p-orbitals oriented perpendicular to each other and referred to as the p_x, p_y, and p_z orbitals.

Paired electrons Two electrons in the same orbital with assigned spins of + and- . See Hund’s rule; Orbital.

Paramagnetism A property of a substance that contains unpaired electrons; it is attracted by a magnetic field.

Partial pressure The pressure that one component of a gaseous mixture would exert if it were alone in the container.

Pathway The specific sequence of events bringing a system from one state to another.

Pauli exclusion principle The principle stating that no two electrons within an atom may have an identical set of all four quantum numbers.

Percent composition The percentage of the total formula weight of a compound attributed to a given element.

Percent yield The percentage of the theoretical product yield that is actually recovered when a chemical reaction occurs.

Period A horizontal row of the periodic table containing elements with the same number of electron shells. Compare group.

Periodic law The law stating that the chemical properties of elements depend on the atomic number of the elements and change in a periodic fashion.

Periodic table The table displaying all known chemical elements arranged in rows (periods) and columns (groups) according to their electronic structure.

pH A measure of the hydrogen ion content of an aqueous solution, defined to be equal to the negative log of the H⁺ concentration.

Phase One of the three states of matter: solid, liquid, or gas. Compare State.

Phase diagram A plot, usually of pressure versus temperature, showing which phases a compound will exhibit under any set of conditions.

Phase equilibrium For a particular substance, any temperature and pressure at which two or three phases coexist in equilibrium. See triple point.

Photon A quantum of energy in the form of light with a value of Planck’s constant multiplied by the frequency of the light.

Physical property A property of a substance related to its physical, not chemical, characteristics (e.g., density).

pOH A measure of the hydroxide (OH^-) ion content of an aqueous solution, defined to be equal to the negative log of the OH^- concentration.

Polar covalent bond 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., H₂O).

Polyprotic acid An acid capable of donating more than one proton (e.g., H₂CO₃).

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 × 10² kPa.

Principal quantum number (n) The first quantum number, defining the energy level or shell occupied by an electron.

Proton (H⁺) A subatomic particle that carries a single positive charge and has a mass defined as 1 or the hydrogen ion, H⁺, which is simply a hydrogen nucleus consisting of one proton. These species are considered to be equivalent.

Quantum number A number used to describe the energy levels available to electrons. The state of any electron is described by four quantum numbers. See azimuthal quantum number; magnetic quantum number; principal quantum number; spin quantum number.