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anything that occupies space and has mass


a pure substance that cannot be broken down into other substances by chemical reactions


substance containing two or more elements chemically combined in a fixed ratio


the smallest particle of an element that retains the properties of the element


subatomic particle having a positive charge; found in nucleus


subatomic particle having a negative charge; not in nucleus but surrounds it


subatomic particle without a charge; found in nucleus


protons and neutrons together; make up the center of an atom

atomic number

identifies a specific element; equals the number of protons in an atom of each element

radioactive isotope

an unstable atom in which the nucleus decays (breaks down) releasing particles and energy


atoms having the same numbers of protons but different numbers of neutrons

ionic bond

occurs when atoms transfer electrons to other atoms


atoms that have lost or gained electrons

covalent bond

occurs when atoms share electrons


atoms that are held together by covalent bonds

chemical reaction

interaction of substances that lead to the formation of new substances


the starting materials for a reaction; found on left side of chemical equation


ending materials of a reaction; found on right side of chemical equation

organic compound

substance made of two or more elements, one being carbon

inorganic compound

substance made of two or more elements, none of which is carbon

valence electrons

electrons in the outermost energy level; they are involved in bond formation

single bond

a covalent bond in which one pair of electrons is shared

double bond

a covalent bond in which four valence electrons are shared between two atoms

chemical formula

indicates the number and types of atoms in a molecule

structural formula

shows the number and types of atoms in a molecule and how they are arranged

chemical reaction

indicates the formation of new substances from previous substances

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