Essential Chemistry Terms and Definitions
Atom: The smallest particle of matter.
Compound: A combination of two or more elements.
Element: A basic substance that is made up of one type of atom.
Atomic Number: A measure of the number of protons in an atom.
Proton: A positively charged particle within an atom’s nucleus.
Ion: An atom or combination of atoms with a net electrical charge (positive or negative).
Neutron: A particle within an atom’s nucleus with no electrical charge.
Mass Number: The total number of protons and neutrons in an atom’s nucleus.
Nucleus: The central part of a cell that contains DNA.
Diatomic Molecule: A molecule containing two atoms.
Work: An action or movement produced by kinetic energy.
Frame of Reference: A set of values on which measurements are based.
Energy Quality: A measure of how much energy is required to do useful work.
Conserve: To use little or none of something, saving it for later use.
Energy Efficiency: A measure of how much energy is required to accomplish a particular amount of work.
Electromagnetic Radiation: Energy that travels in waves.
Heat: A form of energy that produces high temperatures.
Thermal Energy: Energy associated with the temperature of a system.
Potential Energy: Energy that is stored and not actively being used.
Kinetic Energy: Energy of motion.
Transfer: To change the location of something.
Chemical Energy: Energy released or absorbed during chemical reactions.
Periodic Table: A chart that organizes elements into groups based on their properties.
Element Symbol: One- or two-letter designation that scientists use to refer to an element.
Electron Configuration: A system that shows how electrons are distributed within an atom.
Period: One row in the periodic table.
Electron Shell: The path an electron follows as it orbits the nucleus.
Group: A collection of elements that are found in the same column of the periodic table.
Valence Shell: An atom’s outermost electron shell.
Noble Gases: Elements that are not chemically reactive under normal conditions.
Blocks: Sets of neighboring groups in the periodic table.
Ionization Energy: The minimum amount of energy required to remove an electron from an atom.
Electron Affinity: The energy change that occurs when an atom gains an extra electron.
Solvent: A substance that dissolves a solute.
Solution: A mixture of two or more substances.
Limiting Reactant: The first reactant to be completely consumed in a chemical reaction.
Catalyst: A substance that speeds up or increases the rate of a chemical reaction.
Product: A substance created as the result of a chemical process.
Reactant: A substance that participates in a chemical reaction.
Reagent: A substance added to a system to cause a chemical reaction.
In Excess: Something that surpasses what is needed.
Concentration: Refers to the number of molecules of a substance in a given volume.
Yield: The amount of product obtained during a chemical process.
CSTR: Continuous Stirred Tank Reactor.
Batch Reactor: A type of reactor that remains completely sealed while a reaction occurs.
Tank: A large container that can hold liquids or gases.
Tubular Reactor: Also called a plug flow reactor, a type of reactor where reactants flow through a tube.
Bioreactor: A device where a biological reaction or process takes place.
Activated Sludge: A sewage or wastewater treatment process.
Membrane Bioreactor: A reactor that uses both a membrane process and microorganisms.
Impeller: A part of a machine that rotates to mix or agitate fluids.
Cooling Jacket: A covering placed around a container, such as a tank, to control its temperature.