Kaplan MCAT General Chemistry Review

Chemical bond The interaction between two atoms resulting from the overlap of electron orbitals, holding the two atoms together at a specific average distance from each other.

Chemical equation An expression used to describe the quantity and identity of the reactants and products of a reaction.

Chemical properties Those properties of a substance related to the chemical changes that it undergoes, such as ionization energy and electronegativity.

Closed system A system that can exchange energy but not matter with its surroundings.

Colligative properties Those properties of solutions that depend only on the number of solute particles present but not on the nature of those particles. See boiling point elevation; freezing point depression; vapor pressure depression.

Common ion effect A shift in the equilibrium of a solution due to the addition of ions of a species already present in the reaction mixture.

Compound A pure substance that can be decomposed to produce elements, other compounds, or both.

Concentration The amount of solute per unit of solvent (denoted by square brackets) or the relative amount of one component in a mixture.

Conjugate acid-base pair Brønsted-Lowry acid and base reacted by the transfer of a proton (e.g., H₂CO₃ and HCO₃^-).

Coordinate covalent bond A covalent bond in which both electrons of the bonding pair are donated by only one of the bonded atoms. Also called a dative bond.

Covalent bond A chemical bond formed by the sharing of an electron pair between two atoms. See coordinate covalent bond; nonpolar covalent bond; polar covalent bond.

Critical pressure The vapor pressure at the critical temperature of a given substance.

Critical temperature The highest temperature at which the liquid and vapor phases of a substance can coexist; above this temperature, the substance does not liquefy at any pressure.

Crystal A solid whose atoms, ions, or molecules are arranged in a regular, three-dimensional lattice structure.

dsubshells The subshells corresponding to the angular momentum quantum number l = 2, found in the third and higher principal energy levels, each containing five orbitals.

Dalton’s law The law stating that the sum of the partial pressures of the components of a gaseous mixture must equal the total pressure of the sample.

Daniell cell An electrochemical cell in which the anode is the site of Zn metal oxidation and the cathode is the site of Cu²⁺ ion reduction.

Degenerate orbitals Orbitals that possess equal energy.

Delocalized orbitals Molecular orbitals whose electron density is spread over an entire molecule, or a portion thereof, rather than being localized between two atoms.

Density () A physical property of a substance, defined as the mass contained in a unit of volume.

Diamagnetic A condition that arises when a substance has no unpaired electrons and is slightly repelled by a magnetic field.

Diffusion The random motion of gas or solute particles across a concentration gradient, leading to uniform distribution of the gas or solute throughout the container.

Dipole A species containing bonds between elements of different electronegativities, resulting in an unequal distribution of charge in the species.

Dipole–dipole interaction The attractive force between two dipoles whose magnitude is dependent on both the dipole moments and the distance between the two species.

Dipole moment A vector quantity whose magnitude is dependent on the product of the charges and the distance between them. The direction of the moment is from the positive to the negative pole.

Disproportionation A redox reaction in which the same species acts as the oxidizing agent and as the reducing agent. For example,

Hg₂Cl₂ HgCl₂ + Hg

Dissociation The separation of a single species into two separate species; this term is usually used in reference to salts or weak acids or bases.

Effective nuclear charge (Z_eff) The charge perceived by an electron from its orbital. Applies most often to valence electrons and influences periodic properties such as atomic radius and ionization energy.

Electrochemical cell A cell within which a redox reaction takes place, containing two electrodes between which there is an electrical potential difference. See electrolytic cell; galvanic cell.

Electrode An electrical conductor through which an electric current enters or leaves a medium.