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Counting Atoms Part 2

Counting Atoms Part 2. Relating Mass to Numbers of Atoms. The mole , Avogadro’s number , and molar mass provide the basis for relating masses in grams to moles. 6.02 x 10 23. The Mole. The mole is the SI unit for amount of a substance.

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Counting Atoms Part 2

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  1. Counting Atoms Part 2

  2. Relating Mass to Numbers of Atoms • The mole, Avogadro’s number, and molar mass provide the basis for relating masses in grams to moles. 6.02 x 1023

  3. The Mole • The mole is the SI unit for amount of a substance. • A mole (mol) is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12. • The mole is a counting unit, just like a dozen eggs is.

  4. Just remember to think of the “mole” as a counting unit. We don’t usually order 12 or 24 doughnuts; we order one dozen or two dozen. Similarly, a chemist may want 1 mol of carbon, or 2 mol of carbon, or 2.567 mol of carbon. In the following slides, you will see how the mole relates to masses of atoms and compounds.

  5. Avogadro’s Number • The number of particles in a mole has been experimentally determined to have a value of 6.02 x 1023. This means that exactly 12 g of carbon-12 contains 6.02 x 1023carbon-12 atoms.

  6. Avogadro’s number (6.02 x 1023) is the number of particles in exactly one mole of pure substance. • Amadeo Avogadro was an Italian scientist noted to be one of the founders of physical chemistry. He was actually a physics professor but he experimented in both physics and chemistry using mathematics to base most of his findings. • He is most famous for his hypothesis known as Avogadro’s Law. His law simply states that at a fixed temperature and pressure, equal volumes of gases contain the same number of molecules. • The number 6.02214199 x 1023 is called Avogadro’s number, in honor of Amadeo Avogadro, who was the first person to argue in favor of the existence of atoms.

  7. Molar Mass • The mass of one mole of a pure substance is called the molar mass. It is usually written in the unit g/mol. • The molar mass of an element is equal to the atomic mass of the element in atomic mass units (amu). • (molar mass of Li is 6.94 g/mol).

  8. Chemists use molar mass as a conversion factor in chemical calculations. • For example, the molar mass of helium is • 4.00 g He/1 mol He. • To find out how many grams of helium are in two moles of helium, multiply by the molar mass.

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