Graphite with AFM showing all atoms within the hexagonal graphite unit cells.

Image size 2×2 nm2. 77 pm resolution. Subatomic structures are visible within single tungsten atoms.Image size 500 × 500 pm2

STM image (7 nm x 7 nm) of a single zigzag chain of cesium atoms (red) on a gallium-arsenside 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 massmass 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_____ = 2726.6 nails 0.450 g per nail

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 big is a mole?

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

• PairPair: 1 pair shoelaces = 2 shoelaces

• DozenDozen: 1 dozen oranges = 12 oranges

• GrossGross: 1 gross spider rings = 144 rings

• ReamReam: 1 ream paper = 500 sheets of paper

• MoleMole: 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?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