First we have to tell you what a constant is. Simply put, a constant is a number or measurement that is always the same. No matter where, when, or what condition, when you have a formula which asks for a constant, it is always the same number. Here are some examples... 6.02 x 1023 NAME: Avogadro's Number WHAT: It tells you the number of atoms in a mole or the number of molecules in a mole of a substance. 9.1x10-31kg NAME: Mass of an Electron WHAT: We talk about electrons spinning around the nucleus of an atom. Well the me is the mass of one of those electrons. 1.675x10-24g NAME: Mass of a Neutron WHAT: In the nucleus of an atom there are neutrons and protons. A neutron has this much mass. 1.673x10-24g NAME: Mass of a Proton WHAT: In the nucleus of an atom there are neutrons and protons. A proton a mass of this amount. 6.63x10-34Js NAME: Planck's Constant WHAT: Max Planck figured out that energy can be gained and lost by an atom. He used this constant to figure out how much energy. The "J" stands for Joules. 3x108m/s NAME: Speed of Light (in a vacuum) WHAT: Scientists figured out that light travels always at the same speed in a vacuum. The number is really 299,792,458 meters per second, but we abbreviate it. 9.8 m/s2 NAME: Acceleration of Gravity of Earth WHAT: What if you drop a ball from a height? It speeds up as it falls. The amount it speeds up (acceleration) is because of gravity. 1.66x10-27kg NAME: Atomic Mass Unit (also called a Dalton) WHAT: It is 1/12 the mass of a Carbon-12 atom. It is the basis for figuring out the mass all other atoms. 16.x10-19C NAME: Charge of an Electron WHAT: This is the charge of one electron which is flying around the nucleus. .082 Latm/molK 8.3 J/molK 1.987 cal/Kmol NAME: Universal Gas Constant WHAT: This constant is used in the Universal Gas Law "PV=nRT". It has the same value for all gases. You use a different value depending on what measurements your formula uses.