12C’s molar mass is 12 grams, which represents the combined mass of 6.02 x 10 23 12C atoms. By standardizing the number of atoms in a sample of an element, we also get a standardized mass for that element that can be used to compare different elements and compounds to one another. However, it is quite useful if we apply it to other substances, especially elements. Scientists have then defined the molar mass of a substance as the mass of 6.02214076 x 10 23 units of that substance. Regardless of whether the substance is 12C, electrons, or gray squirrels, one mole represents the same number of each of these things.įigure 2: Carbon-12, with 6 protons and 6 neutrons, is the isotope that used to define one mole. Experiments counting the number of 12C atoms in a 12-gram sample have determined that this number is 6.02214076 x 10 23. The International Committee for Weights and Measures-a group that defines the metric system’s units of measurement (for more information, see our module on The Metric System)-defines one mole as the number of atoms in exactly 12 grams of carbon-12 ( 12C, Figure 2). The mole does more than represent a big number: It provides a key link for converting between the number (amount) of a substance, and its mass. Instead of being used for things we encounter in daily life, the mole is used by scientists when talking about enormous numbers of particles like atoms, molecules, and electrons-although the mole’s usefulness goes beyond being a helpful scientific term. Obviously, the mole is not a term we need for most things in daily life. And one mole of gray squirrels weighs 301,000,000,000,000,000,000,000,000 grams-more than four times the mass of the moon!įigure 1: An Eastern Gray Squirrel. One dozen gray squirrels weigh about 6,000 grams, or a little more than a medium-sized bowling ball. One gray squirrel weighs roughly 500 grams, or as much as a hardback book. This is a huge number! To help you and any wildlife biologists reading this module get a sense of just how many things are in one mole, we can use an analogy with another small, gray rodent: the gray squirrel (Figure 1). In this case, one mole represents the enormous (and slightly strange) number, 6.02 x 10 23. The term ‘mole’ represents a number, in the same way the word ‘dozen’ represents 12 of something. But when chemists talk about moles, they’re usually referring to a scientific term. When wildlife biologists talk about moles, they’re usually referring to the tiny, gray rodents that dig underground to find delicious earthworms. This module is an updated version of The Mole. molar mass the mass of one mole of a substance, measured in grams. Avogadro’s number the number of units in one mole: 6.022 × 1023, which is the number of atoms in 12 grams of carbon-12. The mass of one carbon-12 atom is set at 12 amu the atomic mass of atoms of all other elements is determined relative to the mass of carbon-12. Amu (atomic mass unit) the standard unit of measurement of atomic mass.
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