Chemistry Regents Review Notes (copy)

Substance

A compound or an element.

Element

A substance made of only one kind of atom that cannot be broken down by chemical means.

Compound

A substance made of two or more different kinds of atoms, chemically combined in a fixed proportion.

Physical Properties

Characteristics that can be observed without changing the substance's composition, such as melting point and boiling point.

Mixture

A combination of two or more substances where each retains its own properties.

Homogeneous Mixture

A mixture with a uniform composition throughout, where particles are evenly distributed.

Heterogeneous Mixture

A mixture with a non-uniform composition, where particles are unevenly distributed.

Chemical Properties

Properties observed during a chemical reaction that describe the ability of a substance to undergo changes.

Physical Change

A change that does not alter the chemical composition of a substance.

Chemical Change

A change that produces one or more different substances through the breaking and forming of bonds.

Diatomic Molecules

Molecules made up of two of the same atoms bonded together.

Density

The mass of a substance divided by its volume, often expressed in $g/cm^3$ or $g/L$.

Percent Error Formula

A formula used to calculate the error in a measurement relative to the actual value.

Significant Figures

Digits in a number that contribute to its precision, including all non-zero digits and certain zeros.

Temperature

A measure of the average kinetic energy of particles in a substance.

Kinetic Molecular Theory

A theory that describes the behavior of gases in terms of particles in motion.

Avogadro’s Hypothesis

States that equal volumes of gases, at the same temperature and pressure, contain equal numbers of molecules.

Absolute Zero

The theoretical temperature at which all molecular motion ceases, equivalent to 0 K or -273 °C.

Ion

An atom that has gained or lost electrons and thus has a net charge.

Half-Life

The amount of time it takes for half of a radioactive sample to decay.

Stability (nuclear chemistry)

Refers to the state of an atom in which its nucleus is not radioactive.

Isotope

Atoms of the same element with the same number of protons but different numbers of neutrons.

Nuclear Reaction

A reaction that involves a change in an atom's nucleus.

Fission

A type of nuclear reaction in which a large nucleus splits into smaller nuclei.

Fusion

A type of nuclear reaction in which small nuclei combine to form a larger nucleus.

Electronegativity

A measure of an atom's ability to attract and hold onto electrons in a chemical bond.