1 / 20

Counting Atoms

Counting Atoms. Using Mass to Count Things. Atoms are so tiny that it is impossible to count the number of atoms in even 1 gram of matter. We use mass to “count” atoms. Counting by mass. You have a pile of nails that weighs 1227 g. One nail has a mass of 0.450 grams.

rjuanita
Download Presentation

Counting Atoms

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Counting Atoms

  2. Using Mass to Count Things • Atoms are so tiny that it is impossible to count the number of atoms in even 1 gram of matter. • We use mass to “count” atoms.

  3. Counting by mass • You have a pile of nails that weighs 1227 g. • One nail has a mass of 0.450 grams. • How many nails are in the pile? • (1227g) / 0.450 g per nail) = 2726.6 nails. Let’s call it 2730 nails.

  4. What is the mole? Not this kind of mole!

  5. The MOLE • Unit used to “count” numbers of atoms. • Count-by-mass technique. • Defined as the number 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.

  6. The MOLE • So 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!

  7. 6.02 X 1023 = Avogadro’s Number • One mole of water = 6.02 X 1023 water molecules. • One mole of gorillas is 6.02 X 1023 gorillas. • One mole of He atoms is 6.02 X 1023 He atoms. • One mole of anything is 6.02 X 1023 of that thing.

  8. Similar Words • Pair: 1 pair of shoelaces = 2 shoelaces. • Dozen: 1 dozen oranges = 12 oranges. • Gross: 1 gross of spider rings = 144 rings. • Ream: 1 ream of paper = 500 sheets of paper. • Mole: 1 mole of Na atoms = 6.02 X 1023 Na atoms.

  9. How did they find out that 12.0 g of C-12 has 6.02 X 1023 C atoms? • Experimentally by X-Ray diffraction studies

  10. How Big is a Mole?

  11. 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

  12. 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

  13. 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 Equalities How does this help with some other element?

  14. Atomic Weights are Relative

  15. Observation • As long as the number of C and H is the same, the original 12-to-1 mass ratio is preserved. • What is the mass ratio of 425 C atoms compared to 425 H atoms? 12 to 1

  16. Conversely • If the mass ratio is the same, then the number of atoms in two samples is the same. • Given 72 g of C and 6 g of H: • The mass ratio is 12 to 1. So … • These 2 samples have the same number of atoms.

  17. What is the mass of 1 mole of H? • Has to have 6.02 X 1023 H atoms • It’s the same as the number of C atoms in 1 mole of C so the mass ratio is preserved. • Mass ratio for C to H is 12 to 1. • 1 mole of C has a mass of 12 grams. • So 1 mole of H is 1 gram.

  18. Try that again! • Comparing two things: If the number of each is the same, the mass ratio is preserved. • What is the mass of 1 mole of magnesium?

  19. 1 mole of magnesium • 1 atom of C = 12.0 u. 1 atom of Mg = 24.3 u. • 2 atom of C = 24.0 u. 2 atom of Mg = 48.6 u. • 3 atom of C = 36.0 u. 3 atom of Mg = 72.9 u. • 1 mole of C = 12.0 grams. • 1 mole of Mg = 24.3 grams. Mg atoms are a bit more than 2X as heavy as C atoms. Same # of atoms, so mass ratio is preserved.

  20. Molar mass for any element: • To find the molar mass of any element, take the atomic mass and replace a.m.u. with grams. • 1 mole of Ne = 20.2 g = 6.02 X 1023 atoms • 1 mole of Ar = 39.9 g = 6.02 X 1023 atoms • 1 mole of Kr = 83.80 g = 6.02 X 1023 atoms

More Related