CH. 3.4
Counting Atoms
ATOMIC MASS
 Atoms are really small and have really small masses
 Cu atoms have average mass of 1.0552 x 10-25 kg
 Special unit created for atoms called atomic mass unit (amu)
• Copper-63 is 62.940 amu
• Copper-65 is 64.928 amu
• Periodic table says 63.546 – this is the average of all the isotopes
THE MOLE!
 Mole (mol):
• The # of atoms in exactly 12 grams of carbon-12
• (How they decided on the number)
• 6.022 1367 x 1023 atoms – Avogadro’s number
• MEMORIZE 6.022 x 1023
 Why do we do this?
• It’s like saying 1 dozen instead of 12 eggs
• Grouping things together to making counting easier
THE MOLE
 Molar mass is the mass of 1 mole of an element
 Same as the atomic mass number on the periodic table
• But atomic mass is really small and a mole is really big!
• Atomic mass is the # followed by units amu
• Molar mass is the # followed by units g/mol (grams per mol)
MOLAR MASS
 Moving forward, we will stick to molar mass
• …and not really use atomic mass
C O N V E RT I N G M O L E S , M A S S , A N D
PA RT I C L E S – O H M Y !
 Picket fence time!!
6.022 x 1023
 Mass  Molar Mass  Moles  Avogadro’s number  Particles (atoms)
PRACTICE!
 Determine the mass of 3.50 mol of copper
 3.50 mol
63.546 g
1 mol
=
222 g
YOUR TURN
 What is the mass in grams of 0.0050 mol of uranium?
 Calculate the number of moles of 0.850 g of hydrogen atoms.
YOUR TURN
 What is the mass in grams of 0.0050 mol of uranium?
• 1.2 g
 Calculate the number of moles of 0.85 g of hydrogen atoms.
• 0.84 mol
PRACTICE!
 Determine the number of atoms in 0.30 mol of fluorine atoms
 0.30 mol
6.022 x 1023 atoms =
1 mol
1.8 x 1023 atoms
YOUR TURN!
 How many atoms are in 0.70 mol of iron?
 How many moles of silver are represented by 2.888 x 1023
atoms?
YOUR TURN!
 How many atoms are in 0.70 mol of iron?
• 4.2 x 1023 atoms
 How many moles of silver are represented by 2.888 x 1023
atoms?
• 0.4796 mol
PRACTICE!
 Determine the number of atoms in 10.0 g of sodium atoms
 10.0 g
1 mol
6.022 x 1023 atoms=
22.990 g
1 mol
2.62 x 1023 atoms
YOUR TURN!
 Determine the number of atoms in 5.05 g of sulfur atoms.
 Determine the mass of 3.56 x 1024 phosphorous atoms.
YOUR TURN!
 Determine the number of atoms in 5.05 g of sulfur atoms.
• 9.49 x 1022 atoms
 Determine the mass of 3.56 x 1024 phosphorous atoms.
• 183 g of phosphorous atoms