Chemistry Terms


Acid: A substance that releases hydrogen ions (H+ ) in solution; a proton donor.


Anabolism: Metabolic synthesis reactions that combine small molecules to build larger molecules, usually with the net absorption of energy.


Anion: Negatively charged ion; most nonmetal elements can gain electrons and become anions.


Atom: Smallest unit of matter that retains an element's properties; composed of protons, neutrons, and electrons.


Atomic mass unit: A unit of mass equal by definition to 1/12 of the mass of an atom of carbon-12.


Atomic number: The number of protons in an atom, which determines the identity of the atom.


Base: A substance that releases hydroxide ions (OH- ), or accepts hydrogen ions (H+ ) in solution; a proton acceptor.


Buffer: A solution that resists changes in pH; contains a weak acid and its conjugate base.


Catabolism: Metabolic decomposition reactions that breakdown large molecules into smaller molecules, usually with the net release of energy.


Catalyst: Substance that increases the rate of a chemical reaction, but is not consumed.


Cation: Positively charged ion; metal elements can lose electrons and become cations.


Chemical bond: A union between the electron structures of two or more atoms or ions.


Compound: Substance composed of two or more different elements that are chemically bound.


Covalent bond: Chemical bond formed when electrons are shared between atoms; nonpolar bonds share electrons equally; polar bonds share electrons unequally, which produces a dipole.


Electrolyte: Chemical substance, such as a salt, acid, or base, that dissociates and ionizes in water, which makes the resulting solution capable of conducting an electrical current.


Electron: Negatively charged subatomic particle of matter that occupies an orbital around the nucleus; the electrons determine the volume and the chemical properties of the atom; often abbreviated e- .


Electronegativity: An atom's ability to attract shared electrons to itself in a covalent bond.


Element: Fundamental form of matter composed of atoms of only one kind (identical atomic number), that cannot be broken apart into a different form of matter by ordinary physical or chemical means.


Endergonic reaction: Chemical reaction that absorbs energy.


Energy: The capacity to do work and to move matter; potential energy is stored energy; kinetic energy is energy of motion.


Exergonic reaction: Chemical reaction that releases energy.


Hydrogen bond: A weak bond between an oxygen or nitrogen atom, and a hydrogen atom that is bound to another oxygen or nitrogen atom.


Ionic bond: Chemical bond formed when anions and cations are held together by the attraction of their opposite charges.


Isomer: Chemical compounds that have the same chemical formula, but different 3-D structures.


Isotopes: Different atomic forms of an element that have the same number of protons and are chemically identical, but contain different numbers of neutrons, and thus have different atomic mass numbers.


Mass number: Sum of the number of protons and neutrons in the nucleus of an atom, which determines over 99.9% of the mass of that atom. Also called atomic mass number.


Matter: Anything that has mass and volume.


Metabolism: All of the chemical reactions that occur in the body.


Molecule: Particle consisting of two or more atoms joined together by covalent bonds.


Neutron: Subatomic particle of matter with no electric charge that is located in the nucleus of the atom; often abbreviated n0 .


pH scale: A measure of the concentration of free hydrogen ions (H+ ) in solution; pH 0 is the most acidic, pH 7 is a neutral solution, and pH 14 is the most basic (alkaline).


Proton: Positively charged subatomic particle of matter that is located in the in the nucleus of the atom; often abbreviated p+ .


Radioisotope: A radioactive element that has an unstable atomic nucleus and spontaneously emits subatomic particles and energy, resulting in its decay into a different element.


Salt: A compound produced by the reaction of an acid with a base; when dissolved in water, it dissociates into ions and the resulting solution will conduct electricity.


Solute: A substance that is dissolved in a solution.


Solution: A homogeneous mixture of one or more substances (solutes) dispersed molecularly in a dissolving medium (solvent).


Solvent: A dissolving medium that holds another substance in solution.


Valence electrons: Electrons in the outermost shell of an atom that take part in its chemical reactions.