Mass and the Mole

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Molar Mass Noun

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[moh-ler mas]

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Molar Mass

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The mass in grams of one mole of any pure substance, which is numerically equal to its atomic mass.

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Example: This image shows how to find the molar mass of a water molecule (H₂O) by adding the atomic masses of its two hydrogen atoms and one oxygen atom.

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Mole Noun

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[mohl]

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Mole

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The SI base unit for the amount of a substance, representing 6.02 × 10^23 representative particles of that substance.

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Example: A mole is a specific quantity of a substance, equal to 6.022 x 10^23 particles. For carbon-12, one mole has a mass of exactly 12 grams.

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Atomic Mass Noun

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[uh-tom-ik mas]

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Atomic Mass

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The weighted average mass of an element's naturally occurring isotopes, typically expressed in atomic mass units (amu).

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Example: This diagram shows an atom's nucleus, which contains protons and neutrons. The atomic mass is the total count of these particles in the nucleus.

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Isotopes Noun

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[ahy-suh-tohps]

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Isotopes

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Atoms of the same element that have the same number of protons but different numbers of neutrons, resulting in different masses.

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Example: This image shows that isotopes are versions of the same element (Carbon) that have the same number of protons but a different number of neutrons.

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Avogadro's number Noun

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[ah-vuh-gah-drohz nuhm-ber]

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Avogadro's number

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The number of representative particles in one mole of a substance, which is a quantity equal to approximately 6.02 x 10^23.

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Example: This image shows that Avogadro's number (6.022 x 10^23 atoms) is the quantity of atoms found in exactly 12 grams of carbon.

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Conversion Factor Noun

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[kuhn-vur-zhuhn fak-ter]

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Conversion Factor

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A ratio of equivalent measurements that is used to convert a quantity from one unit to another without changing its value.

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Example: This image shows how to set up a calculation using a conversion factor, which is a ratio of equivalent values, to change from a given unit to a desired unit.

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Representative Particles Noun

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[rep-ri-zen-tuh-tiv pahr-ti-kuhls]

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Representative Particles

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The smallest unit in which a substance naturally exists, such as an atom, molecule, or formula unit, used in chemical calculations.

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Example: This image shows the structure of table salt (NaCl), an ionic compound. Its representative particle is a 'formula unit,' the simplest ratio of ions (one Na+ to one Cl-).

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Mass Spectrometry Noun

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[mas spek-trom-i-tree]

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Mass Spectrometry

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An analytical technique used to measure the mass-to-charge ratio of ions to determine a molecule's molar mass and composition.

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Example: A sample is vaporized, ionized, and accelerated. A magnet deflects the ions, separating them by mass, with lighter ions bending more before hitting a detector.