In his 1811 paper, Avogadro drew from British scientist John Dalton’s atomic theory-the idea that all matter, whether gas or liquid or solid, is made of extremely tiny particles (to learn more about Dalton’s idea, see our module on Early Ideas about Matter). He found that 2 volumes of carbon monoxide + 1 volume of oxygen created 2 volumes of carbon dioxide. But how could early 19th century scientists explain this tidy observation of small, whole numbers?įigure 4: Gay-Lussac’s experiment with carbon monoxide and oxygen. Modern scientists would immediately recognize this reaction as: 2CO + 1O 2 → 2CO 2 (Figure 4). For example, Gay-Lussac observed that 2 volumes of carbon monoxide reacted with 1 volume of oxygen to yield 2 volumes of carbon dioxide. In 1809, Gay-Lussac published his observation that volumes of gases react with each other in ratios of small, whole numbers. This contemporary was the French chemist and hot air balloonist Joseph-Louis Gay-Lussac, who was fascinated by the gases that lifted his balloons and performed studies on gas behavior (for more about gas behavior, see the module Properties of Gases). However, as it turns out, that wasn’t his intention!Īvogadro was trying to explain a strangely simple observation made by one of his contemporaries. In 1811, the Italian lawyer-turned-chemist Amedeo Avogadro published an article in an obscure French science journal that lay the foundation for the mole concept. False Correct! Avogadro, Gay-Lussac, Dalton, and the history of the mole concept Extending our example, two moles of 12C atoms contains 2 times 6.02 x 10 23 atoms, which equals 12.04 x 10 23 atoms, which can be written as 1.204 x 10 24 atoms.ī. Further, Avogadro’s number acts as the conversion factor for converting between the number of moles in a sample and the actual number of atoms or molecules in that sample. For example, 24 grams of 12C atoms would be equal to two moles since 24 grams divided by the mass of one mole (12) equals 2. However, other elements have different molar masses for example, 6.02 x 10 23 sulfur-32 ( 32S) atoms have a mass together of 31.97 grams, which is 32S’s molar mass.Īlong with telling us the mass of one mole of an element, molar mass also acts as a conversion factor between the mass of a sample and the number moles in that sample. 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.

Periodic table with new molar mass