Counting Atoms

Counting Atoms

• 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…

• 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

Same two fractions for ANY element or

compound!!

moleX

atomsx

atomsx

moleX

1

1002.6

1002.6

1

23

23

atoms

molAg

atomsxmolAg

25

23

1.481x10

00000000000000001481412000

1

10022.66.24

• How many atoms of silver are in 24.6 moles of silver?

• Scientific Notation on a calculator• 5.6 x 10-12

• Be sure to include any scientific notation from the calculator in your answer!!

5 . 6 E +/- 1 2

Homework (show all work!)

Moles Number of atoms

1.002 moles lithium

5.022x1012 atoms tellurium

212 moles niobium

One atom platinum

1.2x10-18 moles xenon

Homework (SHOW YOUR WORK!!!)

Moles Mass (grams)

0.5 moles argon

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. Convert 3.01 x 1023 atoms of silver to moles.2. Convert 1.50 x 1012 atoms of lead to moles.3. Convert 2500 molecules of water to moles.4. Convert 2.05 x 1015 atoms of carbon dioxide to

moles.5. How many atoms of carbon are in 3.2 moles of

carbon?6. How many molecules of calcium chloride are in

1.0 mole of calcium chloride?7. How many atoms of beryllium are in 2.1x1014

moles of beryllium?8. 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 Practice1. 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