Wednesday, Nov. 6th: “A” DayThursday, Nov. 7th: “B” Day (11:45

release)AgendaCollect “Introduction to the Elements” Worksheet

Section 3.4: “Counting Atoms”Atomic mass unit, atomic mass, mole, molar

mass, Avogadro’s number, conversionsHomework:

Sec. 3.4 review, pg. 104: #1-10Concept Review: “Counting Atoms”

Mole Project/Mole Movie

*Quiz next time over section 3.4*

Section 3.4: “Counting Atoms”You wouldn’t expect something as small as an

atom to have much mass.For example, copper atoms have an average

mass of 1.0552 X 10-25 Kg.Since atoms are so small, kilograms or even

grams are not convenient units to use for their masses.

This is where the atomic mass unit comes into play…

Atomic Mass UnitScientists created a new unit, called the atomic mass

unit, or amu.Atomic mass unit: 1/12 the atomic mass of the

C-12 isotope.Protons and neutrons each have a mass of about 1

amu.So, an atom’s mass number (from the periodic table)

is equal to the atom’s mass in amu’s.

mass # = mass in amu’s(remember, mass # = protons + neutrons)

Masses of Atoms are Expressed in Atomic Mass Units (amu’s)

Atomic mass: the mass of an atom expressed in atomic mass units (amu’s)

How can you tell the atomic mass of an element?

Check the periodic table: the mass number shown on the periodic table is an average of the atomic masses of the naturally occurring isotopes of that element

Introduction to the MoleWords that stand for numbers:

Pair: 2Dozen: 12Decade: 10Gross: 144Ream: 500

Mole:

1 Mole =602,200,000,000,000,000,000,0

00(6.022 X 10 23)

MoleMost samples of elements contain huge numbers

of atoms.To make working with these numbers easier,

chemists created a new unit call the mole (mol)

Mole: the number of atoms in exactly 12 grams of carbon-12. (Remember, the mole is the SI base unit for the

amount of a substance.)

Avogadro’s NumberAvogadro’s Number: 6.022 X 1023, the number of

particles, atoms, or molecules in 1 mole of a substance.

1 mole = 6.022 X 1023 particles, atoms, or molecules

6.022 x 1023 is called

“Avogadro’s Number”

Just How Big is a Mole?A mole of marbles stacked over the

United States would cover the country to a depth of 70 miles!

Just How Big is a Mole?

If 1 mole of dollars were equally distributed to every person in the world, about 7 billion people, each person would receive…

$86,000,000,000,000

How do we Measure Moles?Calculations in chemistry require moles, but

can you go to one of the balances in our lab and measure the number of moles?

NO!

That’s where the molar mass comes into play…

Molar MassTo convert between moles and grams,

chemists use the molar mass of a substance.

Molar mass: the mass, in grams, of 1 mole of a substance.Units: g/mol (grams per mole)

The molar mass of an element is equal to the element’s mass number found on the periodic table.

Molar MassWhat is the molar mass of iron?

55.85 g/molWhat is the molar mass of rubidium?

85.47 g/molWhat is the molar mass of gold?

196.97 g/molWhat is the molar mass of silver?

107.87 g/molWhat is the molar mass of calcium?

40.08 g/mol

Molar MassHow do you find the molar mass of a

compound, like water?Simply add up the atomic masses of the

elements that make up the compound.Water, H2O, consists of 2 hydrogen atoms and

1 oxygen atom:H: 1.01 g/molH: 1.01 g/mol

O: 16.00 g/mol

18.02 g/mol

Molar MassWhat is the molar mass of salt, NaCl?

Na: 22.99 g/molCl: 35.45 g/mol58.44 g/mol

What is the molar mass of sodium hydroxide, NaOH?

Na: 22.99 g/molO: 16.00 g/molH: 1.01 g/mol

40.00 g/mol

‘A Mole in One’ 18

1 mole = 6.022x1023 atoms = an atom’s mass # in grams

Converting from Moles MassSample Problem D, pg. 102

What is the mass, in grams, of 3.50 mole of copper, Cu?

Use the periodic table to find the molar mass of copper, Cu.

The conversion factor needed to solve the problem is:

1 mole Cu = 63.55 g Cu

3.50 mole Cu X 63.55 g Cu = 222 g Cu 1 mole Cu (3 sig

figs)

Practice Problem #3, pg 102Calculate the number of moles of 0.850 g of

hydrogen atoms. What is the mass in grams of 0.850 mol of hydrogen atoms?

Use the periodic table to find the molar mass of hydrogen, H.

The conversion factor needed to solve the problem is: 1 mole H = 1.008 g H

0.850 g H X 1 mol H = .843 mol H 1.008 g H

0.850 mol H X 1.008 g H = .857 g H 1 mol H (3 sig figs each)

Converting from Moles # of AtomsSample Problem E, pg. 103

Determine the number of atoms in 0.30 mol of fluorine atoms.

The conversion factor needed to solve the problem is:

1 mole F = 6.022 X 10 23 atoms F0.30 mol F atoms X 6.022 X 1023 atoms F

1 mole F

1.8 X 1023 atoms F(2 sig figs)

Practice Problem #2, pg. 103How many moles of silver are represented by 2.888

X 1023 atoms?The conversion factor needed to solve the problem

is:1 mole Ag = 6.022 X 10 23 atoms Ag

2.888 X 1023 atoms X 1 mole Ag6.022 X 1023 atoms

.4796 mol Ag(4 sig figs)

Homework(you may work with a partner)

Section 3.4 reviewpg 104: 1-10

Concept Review: “Counting Atoms”

Keep updating your KWL!

Remember: Quiz next time over section 3.4

Mole Project

Your project is to create a mole to share with the class.

The project will be done outside of regular class time.

The projects will be due and presented to the class on:“A” Day: Wednesday, Nov. 20th

“B” Day: Thursday, Nov. 21st