Transcript The Mole

The
Mole
Unit 3
The Mole
• So far we have been dealing with numbers
on the atomic scale…
– Atomic Number = # of protons
– Mass Number = # of protons + # of
neutrons
– Atomic Mass = # of amu in one average
atom
The Mole
• This is a really small scale.
• Is it logical to try to measure out chemicals
for labs this way?
• NO!
• We need a bigger scale to use for everyday
measurements and calculations.
The Mole
• We need…
• The MOLE!
• The MOLE is a unit of measure – a unit of
“how many”.
The Mole
• Just like a dozen eggs tells us
“how many” eggs, a mole tells
us “how many” particles.
• 1 dozen eggs = 12 eggs
• 1 mole = 6.02 x 1023 particles
– Particles can be anything –
atoms, molecules, eggs, etc.
The Mole
• This number (6.02 x 1023) is
called Avogadro’s Number, in
honor of Amedeo Avogadro’s
contributions to chemistry.
• Unfortunately for him, his ideas
weren’t really recognized as
important until after he died.
The Mole
• But wait, where did we get this number?
• Scientists have found that there is exactly 1
mole of atoms in the atomic mass of an
element when that mass is expressed in
grams.
• Huh?
The Mole
• For example:
• What is the atomic mass of C-12?
• (Hint – there is only one isotope here, so
think mass number)
• Atomic mass = 12 amu
The Mole
• Then express that mass in grams  12 g
• In exactly 12 grams of C-12, there is one
mole (6.02 x 1023) of atoms.
• This also works for our average atomic
masses (from the periodic table).
The Mole
• So, in exactly 12.01 g of natural carbon
there are 6.02 x 1023 atoms.
• AND, 6.02 x 1023 atoms = 1 mole. So 1
mole of carbon = 12.01 g.
• Hmm…..those sounds suspiciously like
conversion factors…
• Time for examples!
The Mole
• How many atoms are in 1.00 mole of
gold?
1.00 mole Au 6.02 x 1023 atoms
1 mole
6.02 x 1023
=
Atoms Au
The Mole
• How many molecules are in 2.00 moles of
water?
2.00 mole H2O 6.02 x 1023 molecules
1 mole
=
1.20 x 1024
Molecules
H2O
The Mole
• How many marbles are in 1.00 mole of
marbles? (Enough to cover the entire Earth
to a depth of 50 miles!)
1.00 mole marbles 6.02 x 1023 marbles
1 mole
=
6.02 x 1023
marbles
The Mole
• How many grams are in 1.00 mole of neon?
1.00 mole Ne
6.02 x 1023 atoms 20.18 g Ne
1 mole Ne
6.02 x 1023 atoms
= 20.2 g Ne