Graphite with AFM showing
all atoms within the
hexagonal graphite unit cells.
77 pm resolution.
Subatomic structures are
visible
within single tungsten
atoms.
Image size 500 × 500 pm2
Image size 2×2 nm2.
STM image (7 nm x 7
nm) of a single zigzag
chain of cesium atoms
(red) on a galliumarsenside surface
(blue)
Photo courtesy National
Institute of Standards
and Technology (NIST
Using Mass to Count Things
• atoms are so tiny it is impossible to
count number of atoms in even 1 gram
of matter
• we use mass to “count” atoms
Counting by mass
• a pile of nails weighs 1227 g
• one nail has mass of 0.450 grams
• how many nails are in pile?
1227g_____
0.450 g per nail
= 2726.6 nails
What is a mole?
No, not this
kind of mole!
The MOLE
• unit used to “count” numbers of atoms
– count-by-mass technique
• defined as # of atoms in 12.0 grams of C-12
– this is the STANDARD!
• 12.0 g of C-12 has 6.0221415 X 1023 atoms
Just how
is a mole?
big
Mole movie
The MOLE
• 1 mole of any element has 6.02 X 1023 particles
• this is a really big number – it’s so big
because atoms are really small!
6.02 X 1023 = Avogadro’s Number
• one mole of water = 6.02 X 1023 water molecules
• one mole of gorillas = 6.02 X 1023 gorillas
• one mole of He atoms = 6.02 X 1023 He atoms
• one mole of anything = 6.02 X 1023 of that thing
Similar Words
•
•
•
•
•
pair: 1 pair shoelaces = 2 shoelaces
dozen: 1 dozen oranges = 12 oranges
gross: 1 gross spider rings = 144 rings
ream: 1 ream paper = 500 sheets of paper
mole: 1 mole Na atoms
= 6.02 X 1023 Na atoms
Equalities
• 1 mole of C-12
=
• 12.0 grams of C-12
=
• 6.02 X 1023 atoms
of C-12
• 0.5 mole of C-12
=
• 6.0 grams of C-12
=
• 3.01 X 1023 atoms of
C-12
Equalities
• 1 mole of C-12
=
• 12.0 grams of C-12
=
• 6.02 X 1023 atoms
of C-12
• 0.25 mole of C-12
=
• 3.0 grams of C-12
=
• 1.50 X 1023 atoms of
C-12
Equalities
• 1 mole of C-12
=
• 12.0 grams of C-12
=
• 6.02 X 1023 atoms
of C-12
• 2 moles of C-12
=
• 24.0 grams of C-12
=
• 12.04 X 1023 atoms
of C-12 = 1.204 X
1024 atoms of C-12
How does this help with other elements?
molar mass for any element:
• molar mass of any element:
– take atomic mass and replace amu with grams
• 1 mole Ne = 20.179 g = 6.02 X 1023 atoms
• 1 mole Ar = 39.948 g = 6.02 X 1023 atoms
• 1 mole Kr = 83.80 g = 6.02 X 1023 atoms