Interactions Among Atoms



negatively charged ion


smallest unit of an element that has the properties of the element

atomic number

number of protons in each atom of an element

atomic weight

average mass of all the isotopes of an element, based on the relative abundance of each isotope


positively charged ion


substance in which atoms of two or more elements are bonded together in a certain ratio

covalent bond

chemical bond that forms when atoms share electrons


negatively charged subatomic particle that moves in orbitals around the atomic nucleus


tendency of an atom to attract electrons


substance that cannot be broken down into simpler substances by chemical reactions

hydrogen bond

weak bond that results from an attraction between a positively charged hydrogen in one molecule and a negatively charged atom in another


having a weak or no affinity to water

hydrophobic bond

force that pushes nonpolar molecules together in an aqueous environment

instantaneous dipole

dipole that forms because of a short-lived imbalance in charge distribution in an otherwise nonpolar atom or molecule


charged particle formed when an atom gains or loses electrons

ionic compound

substance that results when a positively charged ion and a negatively charged ion bind together through electrostatic forces


one of two or more atoms of an element that have the same number of protons but different numbers of neutrons


substance composed of two or more substances that are not chemically bonded


amount of a substance that contains as many particles as 12 grams of pure carbon-12, equal to 6.023×10236.023\times10^{23} (Avogadro's number) particles

molecular mass

sum of the atomic weights of all atoms in a molecule


group of two or more atoms held together by one or more covalent bonds


subatomic particle that has a neutral charge in the nucleus of an atom

nonpolar covalent bond

covalent bond in which the nuclei of the bonded atoms exert equal or nearly equal force on the shared electrons


positively charged center of an atom containing protons and neutrons

polar covalent bond

covalent bond in which the electron density is more localized on one end of the bond. One end is slightly positive, and one end is slightly negative.


positively charged subatomic particle in the nucleus of an atom

radioactive decay

process by which an atom loses energy by emitting radiation


isotopes that emits radiation that can be detected to track the movement of the isotope through a system such as a patient's body

valence electron

electron in the outermost shell of an atom

van der Waals attraction

weak, noncovalent attractive force between two distinct molecules resulting from instantaneous dipoles