Kaplan MCAT General Chemistry Review

Ideal Gas law The law stating that PV = nRT, where R is the gas constant. It can be used to describe the behavior of many real gases at moderate pressures and temperatures significantly above absolute zero. See kinetic molecular theory.

Indicator, acid-base A substance used in low concentration during a titration that changes color over a certain pH range. The color change, which occurs as the indicator undergoes a dissociation reaction, is used to identify the end point of the titration reaction.

Inert gases The elements located in group 0 (or Group VIII) of the periodic table. They contain a full octet of valence electrons in their outermost shells; this electron configuration makes them the least reactive of the elements. Also called Noble gases.

Intermolecular forces The attractive and repulsive forces between molecules. See van der Waals forces.

Intramolecular forces The attractive forces between atoms within a single molecule.

Ion A charged atom or molecule that results from the loss or gain of electrons.

Ionic bond A chemical bond formed through electrostatic interaction between positive and negative ions.

Ionic solid A solid consisting of positive and negative ions arranged into crystals that are made up of regularly repeated units and held together by ionic bonds.

Ionization product (I.P.) The general term for the dissociation of salts or of weak acids or bases; the ratio of the concentration of the ionic products to the concentration of the reactant for a reaction, all raised to their stoichiometric coefficients.

Ionization energy The energy required to remove an electron from the valence shell of a gaseous atom.

Isobaric process A process that occurs at constant pressure.

Isolated system System that can exchange neither matter nor energy with its surroundings.

Isothermal process Process that occurs at constant temperature in which the system either loses or gains heat in order to maintain that temperature.

Isotopes Atoms containing the same number of protons but different numbers of neutrons (e.g., nitrogen-14 and nitrogen-15).

Joule (J) A unit of energy;

1 J = 1 kg m²/s².

Kelvin (K) A temperature scale with units equal to the units of the Celsius scale and absolute zero defined as 0 K; also the units of that temperature scale. Otherwise known as the absolute temperature scale. 0 K = -273.15°C.

Kinetic molecular theory The theory proposed to account for the observed behavior of gases. The theory considers gas molecules to be point-like, volumeless particles exhibiting no intermolecular forces that are in constant random motion and undergo only completely elastic collisions with the container or other molecules. See Ideal Gas law.

Law of conservation of mass The law stating that in a given reaction, the mass of the products is equal to the mass of the reactants.

Law of constant composition The law stating that the elements in a pure compound are found in specific weight ratios.

Le Châtelier’s principle The observation that when a system at equilibrium is disturbed or stressed, the system will react in such a way as to relieve the stress and restore equilibrium. See equilibrium.

Lewis acid A species capable of accepting an electron pair (e.g., BF₃).

Lewis base A species capable of donating an electron pair (e.g., NH₃).

Lewis structure A method of representing the shared and unshared electrons of an atom, molecule, or ion. Also called a lewis dot diagram.

Limiting reagent In a chemical reaction, the reactant present in such quantity as to limit the amount of product that can be formed. Compare excess reagent.

Liquid The state of matter in which intermolecular attractions are intermediate between those in gases and in solids, distinguished from the gas phase in having a definite volume and from the solid phase in that the molecules may mix freely.

Lyman series A portion of the emission spectrum for hydrogen representing electronic transitions from energy levels n > 1 to n = 1.

Magnetic quantum number (m) The third quantum number, defining the particular orbital of a subshell in which an electron resides. It conveys information about the orientation of the orbital in space (e.g., p_x vs. p_y).

Mass A physical property representing the amount of matter in a given sample.

Mass number The total number of protons and neutrons in a nucleus.

Maxwell-Boltzmann distribution The distribution of the molecular speeds of gas particles at a given temperature.