Graphite with AFM showing all atoms within the hexagonal graphite unit cells. Image size 2×2 nm2. 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 77 pm resolution. Subatomic structures are visible within single tungsten atoms. Image size 500 × 500 pm2

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_____ = 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 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