Atoms Moles The Mole A Measurement of Matter

Atoms & Moles

The Mole: A Measurement of Matter • Counting the number of atoms of a substance would very time consuming, because the objects you are counting are so small. • Imagine counting all the grains of sugar you baked into a cake. It would take a really long time! • The mole (mol) is one of the seven base units in the SI system and allows us to easily measures the amount of particles in a substance, even though they are very small. Atoms in garnet, a semi-precious mineral

Avogadro’s Number • 6. 02 x 1023 is called Avogadro’s number. It is named after Amadeo Avogadro who did work in the 1800’s that allowed 6. 02 x 1023 to be calculated and is equal to one mole. • The mole is the “chemist’s dozen”. It is a convenient way to count extremely large numbers of atoms, molecules or ions. 1 mole = 6. 02 x 1023 representative particles

How big is a Mole? 6. 02 X 1023 Watermelon Seeds: Would be found inside a melon slightly larger than the moon. 6. 02 X 1023 Donut Holes: Would cover the earth and be 5 miles (8 km) deep. 6. 02 X 1023 Pennies: Would make at least 7 stacks that would reach the moon. 6. 02 X 1023 Grains of Sand: Would be more than all of the sand on Miami Beach. 6. 02 X 1023 Blood Cells: Would be more than the total number of blood cells found in every human on earth.

Representative Particles • The form in which a substance exists is its “representative particle”. • Representative particles can be atoms, ions, molecules, formula units, or anything else. Substance Element Representative Particle Atom

Mole-Mass Relationships (A-M-G) Conversion Factors: 1 mol = 6. 02 X 1023

Solving Problems with Avogadro’s Number • We work these problems using dimensional analysis. • 1 mole = 6. 02 x 1023 representative particles • Representative Particles: unit needs to be applicable to what is being calculated.

Example 1: page 9 How many moles are 1. 20 x 1025 atoms of phosphorous? 1. 20 x 1025 atoms P x 1 mol P 6. 02 x 1023 atoms P 19. 9 mol P

Example 2: page 9 How many atoms are in 0. 750 mol of Zn? 0. 750 mol Zn x 6. 02 x 1023 atoms Zn 1 mol Zn 4. 52 x 1023 atoms Zn

Mole – Mass Conversions (A-M-G) Conversion factor 1 mol = molar mass (g)

Molar Mass (grams) • The molar mass of a singular atom is simply equal to its atomic mass in grams. • Example: The molar mass of Sulfur is 32. 06 g

Example 3: page 9 Find the mass in grams of 3. 32 mol of K. 3. 32 mol K x 39. 10 g K 1 mol K = 130. –or- 1. 30 x 102 g K

Example 4: page 9 Find the number of moles in 187 g of aluminum. 1 mol Al 187 g Al x 26. 98 g Al = 6. 93 mol Al

Two-Step Mole Problems (A-M-G) Using multiple conversion factors. 1 mol = molar mass 1 mol= 6. 02 X 1023 atoms

Example 5: page 9 Calculate the number of atoms present in 4. 29 g of phosphorous. 4. 29 g P x 1 mol P 30. 97 g P x 6. 02 x 1023 atoms P 1 mol P 22 = 8. 34 x 10 atoms P

Example 6: page 9 Calculate the mass of 2. 410 x 1022 atoms of gold. 1022 2. 41 x atoms Au x 1 mol Au 6. 02 x 1023 atoms Au x 196. 97 g Au 1 mol Au = 7. 89 g Au

Complete practice problems 1 -5 on bottom of page 9 AND complete page 10 in your packet for homework!

Discuss the Warm-up • Compare the mass of 1 mole of Al with the mass of 1 mole of S. Which is larger? Why do you think that element has a larger mass? • Compare the mass of 1 mole of Fe with the mass of 1 mole of Sn. Which is larger? Why do you think that element has a larger mass? • Look at the rest of your data. What patterns do you observe in the relationship between the mass of one mole of a sample and the element itself? • Which do you think would weigh more, one mole of Gold or one mole of Silver? Explain. • If we had an additional container containing 1 mole of potassium, what do you think would be the mass of the element in the bag? Why do you think this?