Counting Atoms
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Co
CO
CO2
C6H12O6
Mg(NO3)2
How many atoms are there in 5
molecules of Mg(NO3)2?
• …5 molecules of C6H12O6?
• Bring:
–Calculator
–Periodic table
• EVERY DAY
Masses of atoms
• Atoms are so tiny; how do we give
their masses?
• Relative to (compared with) the mass
of 6.02 x 1023 atoms of carbon-12
(which have a mass of 12 grams).
The mole
• Mole: The SI unit for amount of
substance (n)
• Contains as many particles as there
are atoms in 12 grams of carbon-12
• There are 6.02x1023 atoms in 12
grams of carbon-12
• Avogadro’s Constant = 6.02x1023
Molar Mass
• The mole: 6.02 x 1023 particles of any
substance
– Ex: one mole of H2O is 6.022 x 1023 H2O
molecules
• Atomic mass is the mass in grams of
one mole of an element(units: g/mol)
Find the atomic mass of…
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Oxygen
Phosphorus
Sodium
Gold
Copper
• Molar mass is a weighted average of
all the isotopes of an element
– Isotopes: atoms of the same element
(same number of protons) with different
numbers of neutrons.
• mass number differs
• how to calculate molar mass - later
Convert Between Moles and
Number of Atoms
1moleX
23
6.02 x10 atoms
23
6.02 x10 atoms
1moleX
Same two
fractions for ANY
element or
compound!!
• How many atoms of silver are in 24.6
moles of silver?
 6.022 x10 23 atoms 

24.6molAg 
1molAg


14814120000000000000000000
25
1.481x10 atoms
• Scientific Notation on a calculator
• 5.6 x 10-12
5
.
6
E
+/-
1
2
• Be sure to include any scientific notation
from the calculator in your answer!!
Homework (show all work!)
Moles
1.002 moles lithium
Number of atoms
5.022x1012 atoms
tellurium
212 moles niobium
One atom platinum
1.2x10-18 moles
xenon
Homework
(SHOW YOUR WORK!!!)
Moles
0.5 moles argon
Mass (grams)
10.0 grams rubidium
1.2x1015 moles
hydrogen
1.6x10-20 grams gold
1.000 mole iridium
Homework
Number of atoms
Mass (grams)
3,000,000 atoms iron
2.3x10-5 g zinc
2.4x1043 atoms
copper
One gram silver
20 atoms iodine
1.
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7.
8.
Convert 3.01 x 1023 atoms of silver to moles.
Convert 1.50 x 1012 atoms of lead to moles.
Convert 2500 molecules of water to moles.
Convert 2.05 x 1015 atoms of carbon dioxide
to moles.
How many atoms of carbon are in 3.2 moles
of carbon?
How many molecules of calcium chloride are
in 1.0 mole of calcium chloride?
How many atoms of beryllium are in 2.1x1014
moles of beryllium?
How many molecules of ethene are in 6.11
moles of ethene?
• How many molecules are there in 4.5
moles of H2O?
• How many atoms are there in 4.5
moles of H2O?
Practice Moles to Number of Atoms
Conversions
1. How many moles of vanadium are
in 4.5 x 102 atoms of V?
2. How many moles of oxygen gas are
in 45,000 molecules of O2?
3. How many moles of neon are in 1.2
x 103 atoms of Ne?
4. How many moles of chromium are
in 7.90 x 1021 atoms of Cr?
Atoms to Moles
• How many atoms of sodium are in 0.5
moles of sodium?
• How many atoms of oxygen are in 1.5
moles of oxygen?
• How many atoms of fluorine are in
0.075 moles of fluorine?
• How many atoms of argon are in 3.45
moles of argon?
• Homework p. 123 # 18, handout
Converting between mass (g) and
moles (mol)
1 mol O
15.999 g O
– Or
15.999 g O
1 mol O
• Choose one depending on if you are
given grams of oxygen or moles of
oxygen.
• Lithium (Li)
• Calculate the mass of 3.0 moles of
lithium.
• How many atoms are there in 3.0
moles of lithium?
• Chromium (Cr)
• Calculate the number of moles of
chromium if you had 3.25x1034 atoms
of chromium.
• Calculate the mass of 3.25x1034
atoms of chromium.
• Zinc (Zn)
• How many moles of zinc are there in
34.7 grams of zinc?
• How many atoms of zinc in 34.7
grams?
Write both fractions.
• Germanium (Ge)
• Calculate the mass of 3.0 moles of
germanium.
• How many atoms is that?
Which Fraction?
• How many moles of chlorine are in
6.4 grams of chlorine?
Which Fraction?
• How many grams of krypton are in
8.9x1012 moles of krypton?
• How many atoms is that?
Which Fraction?
• How many grams of hydrogen are in
32.1 atoms of hydrogen?
• How many moles is that?
Which Fraction?
• How many moles of aluminum are in
6.5 grams of aluminum?
Which Fraction?
• What is the mass of 5.6x103 moles of
mercury?
• How many atoms is that?
Write both fractions.
• How many moles are equal to
2.58x1067 atoms of Xenon (Xe)?
• Calculate the mass.
Which Fraction?
• How many moles of Xe are in 9.0
grams of Xe?
• How many atoms is that?
Molar Mass Practice
1. What is the mass in grams of 3.50 mol of
copper (Cu)?
2. What is the mass in grams of 2.25 mol of iron
(Fe)?
3. What is the mass in grams of 0.375 mol of
potassium (K)?
4. What is the mass in grams of 0.0135 mol of
sodium (Na)?
5. What is the mass in grams of 16.3 mol of
nickel (Ni)?
• How many moles of Aluminum are in
11.9 grams of Aluminum?
• How many moles of calcium (Ca) are
in 5.00 grams of calcium?
• How many moles of copper (Cu) are
in 13.3 grams of Copper?
• How many moles of gold (Au) are in
3.60 x 10-10 grams of gold?
Mass to atoms
1. What is the mass in grams of 1.20 x
108 atoms of copper?
2. What is the mass in grams of 7.5 x
1015 atoms of nickel?
3. How many atoms of sulfur are in
4.00 grams of sulfur?
4. How many atoms of carbon are in
1500 grams of carbon?
• Homework: p. 123 #27-30, handout