Chapter 10:The Mole 10-1 Measuring Matter Counting Particles… The SI Unit for counting is the mole. The mole is a number of particles or ‘things’ equal to 6.02 x 1023 of those particles . Just like a dozen is 12 a mole is 6.02 x 1023 . This number is called Avogadro’s number.

Converting with the mole We will use dimensional analysis to convert with the mole. We always start the same… known x unknown units = unknown answer 1 known units Write the known and unknown for every problem, then plug them into the equation. Try this… How many atoms are in 2.5 moles of sulfur?

Solve Unknown: # of atoms S Known: 2.5 moles S Plug in… and use 6.02x1023atoms/1mol S known x unknown units = unknown answer 1 known units Answer:1.505 x 1024atoms…then round to 2 sd 1.5 x 1024atoms of S

Representative Particles The representative particle of elements is the atom. The representative particle of ionic compounds is the formula unit. The representative particle of molecular compounds is the molecule. When we count with the mole…this is what we count, in chemistry.

The Mole and Mass Let’s compare the mass of 1 atom of H:He:C 1amu:4amu:12amu What about 10 atoms of each… The reduced ratio would be1:4:12 What about 1,000,000 atoms of each…. Is there a number of atoms where the numbers 1:4:12 would be equal to 1g:4g:12g? ….YES…that number is the mole

Mass and the Mole The number under each atom now stands for gram atomic mass. If we have a compound, we add up the masses in the compound and we have gram molecular mass. If it is an ionic compound it will be gram formula mass. A general term is molar mass.

Mass and the Mole You can now use the molar mass as a second conversion factor: 1 mol H2O/18.0 g H2O How many grams are found in 2.0 moles of H2O? (Try it.)