THE MOLETHE MOLE

MEASURING MATTER

3 ways to measure things:count: 1 dozen = 12 applesmass: 1 dozen = 2 kg of applesvolume: 1 dozen = 0.20 bushel

(for typical wicker basket)We need to measure ATOMS!

MASS OF 1 CARBON ATOM

1 amu = one proton or one neutron

= 1.66 x 10-24 gcarbon has 12 protons & neutronsmass of one C atom = 1.995 x 10-

23 gIMPOSSIBLE, IMPRACTICLE!

MASS OF 1 CARBON ATOMOne atom cannot be weighed.

Can we weigh many atoms and still compare one atom to another? …

MASS RATIO: He vs. N

1400 amu400 amu100 atoms

140 amu40 amu10 atoms28 amu8 amu2 atoms

N = 14 amu

He = 4 amu

1 atom

Mass ratio ( 2 : 7 ) is alwaysthe same!

AVOGADRO’S NUMBER1 carbon atom = 12.01 amu

?? atoms = 12.01 grams of carbon

ANSWER: 6.02 x 1023 atoms!Avogadro’s number: number of

atoms whose mass in grams = mass of one atom in amu

We call this number of “things” one MOLE:

•6.02 x 1023 “things” = 1 mole•just like 12 “things” = 1

dozen

AVOGADRO’S NUMBER

“THINGS”:REPRESENTATIVE PARTICLES

1 mole = 6.02 x 1023 representative particles

1 mole carbon = 6.02x1023 atoms1 mole CO2 = 6.02x1023 molecules

1 mole NaCl = 6.02x1023 formula units

1 atom of hydrogen = 1.01 amu6.02x1023 atoms of H = 1.01 grams 1 mole of H = 1.01 gramsusually written as: 1.01 g/moleThis number is called the

MOLAR MASS of hydrogen.

THE MOLE ANDMOLAR MASS

MOLAR MASS

In textbook: gram atomic mass gram molecular

mass gram formula

massALL mean the same – the mass

of one mole of a substance:MOLAR MASS

MOLAR MASScarbon: MM = 12.01 g/mole12.01 g = 1 mole = 6.02x1023atoms

magnesium: MM = 24.34 g/mole24.34 g = 1 mole = 6.02x1023atoms

1 mole = same number of atoms = different number of grams

MOLAR MASS

What is the molar mass of sulfur?

32.07 g/moleWhat is the molar mass of SO3?

80.07 g/moleWhat is the molar mass of NaCl?

58.44 g/mole

AMADEO AVOGADRO