chemistry unit 2 keyterms

Atomic number

represents the number of protons in the nucleus of an atom

Chemical change

a change in a substance that alters the composition of the substance; irreversible

Chemical property

a property that describes how the substance changes through interactions with other substances

Compound

type of substance where two or more atoms are chemically combined

Electron

subatomic particle with a negative charge, located outside the nucleus, with no mass

Element

type of substance that contains only one kind of atom

Fission

when a substance splits into smaller substances

Fusion

when two substances join together to become a larger substance

Half-life

the amount of time it takes for half of a radioactive isotope's nucleus to decay

Heterogeneous mixture

a mixture that is not uniform in composition throughout

Homogeneous mixture

a mixture that is uniform in composition throughout, also called a solution

Isotope

version of an element with the same number of protons and electrons, but a different number of neutrons

Law of conservation of mass

mass cannot be created or destroyed, only rearranged

Mass number

represents the number of protons plus neutrons in the nucleus of an atom

Mixture

created by the physical blend of two or more substances; no chemical combination

Molecule

the smallest unit of a substance that keeps all the physical and chemical properties of that substance

Neutron

subatomic particle with no charge, located in the nucleus, with a mass of 1 amu

Physical change

a change in a substance that does not alter the composition of the substance; reversible

Physical property

a property that describes the substance without mentioning if the substance can change

Proton

subatomic particle with a positive charge, located in the nucleus, with a mass of 1 amu

Pure substance

matter that has definite chemical and physical properties