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

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.

1 mole = 6.02 x 1023 representative particles 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

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 Representative Particle Element Atom

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.

How many moles are 1.20 x 1025 atoms of phosphorous? 1.20 x 1025 atoms P 1 mol P x 1 6.02 x 1023 atoms P 19.9 mol P

How many atoms are in 0.750 mol of Zn? 0.750 mol Zn 6.02 x 1023 atoms Zn x 1 1 mol Zn 4.52 x 1023 atoms Zn

Mole-Mass Relationships

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

Mole – Mass Conversions Conversion factor 1 mol = molar mass (g)

Find the mass in grams of 3.32 mol of K. 3.32 mol K 39.10 g K x 1 1 mol K = 1.30 x 102 g K

Find the number of moles in 187 g of aluminum. 187 g Al 1 mol Al x 1 26.98 g Al = 6.93 mol Al

Multi-step Mole Problems Using multiple conversion factors.

Calculate the number of atoms present in 4.29 g of phosphorous. 4.29 g P 1 mol P 6.02x1023 atoms P x x 1 30.974 g P 1 mol P = 8.34 x 1022 atoms P

Calculate the mass of 2.410 x 1022 atoms of gold. 2.410 x 1022 atoms Au 1 mol Au 196.97 g Au x x 1 6.02 x 1023 atoms Au 1 mol Au = 7.885 g Au