1 / 12

How to Count Atoms (when they are really really small)

How to Count Atoms (when they are really really small). Review: 1 12 C atom = 12.0000 amu = 1.9926x 10 -23 g (from mass spectroscopy experiments) So. Goal: a number that is capable of expressing numbers of atoms in convenient terms.

krysta
Download Presentation

How to Count Atoms (when they are really really small)

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. How to Count Atoms(when they are really really small) Review: 1 12C atom = 12.0000 amu = 1.9926x 10-23 g (from mass spectroscopy experiments) So

  2. Goal: a number that is capable of expressing numbers of atoms in convenient terms. H and O react in simple numbers of atoms to form water (H2O): 2 H : 1 O There is not a simple relation between the masses that react. Yet – masses are what we can readily measure in a laboratory. To get a quantity capable of expressing numbers of atoms, Define: 1 mole = number of atoms in 12.0000 g of 12C.

  3. We now have enough information to calculate the number of atoms in one mole of carbon: But this is also the number of atoms in one atomic mass, expressed in grams, of any element. This important number is known as Avogadro’s Number, NA.

  4. Both a mole and a dozen express quantities of things by a collective number. A dozen eggs weighs more than a dozen ping-pong balls because each individual unit is heavier.

  5. 16.0 amu 12.0 amu O C 192.0 amu in carton 144.0 amu in carton (A dozen oxygen atoms weigh more than a dozen carbon atoms) Take the same number of atoms as at the left. The total mass will be 16.0 grams Take enough cartons to have 6.02 x 1023 atoms The total mass will be 12.0 gram Moral: a mole of oxygen weighs more than a mole of carbon because each individual oxygen atom weighs more.

  6. So now, atomic masses have two interpretations: 1 atom of C weighs 12.0000 amu 1 mole of C weighs 12.0000 g Some conversion factors: 1 mole of C = 12.00 g 1 mole of C = 6.02 x 1023 atoms C

  7. Now we can calculate the mass of any atom: 1 atom of U = 238 amu

  8. Now we can calculate the mass of any atom: 1 atom of U = 238 amu Find the number of carbon atoms in 3.0 g C.

  9. A mole road-map Atomic mass NA atoms Moles grams

  10. This can be applied to compounds, which have a molecular mass (in amu) or a molar mass (in grams). For instance: In one molecule of H2O, there are 2 H atoms = 2 x 1 amu = 2 amu 1 O atom = 1 x 16 amu = 16 amu 18 amu 1 mole of H2O has 1 mole of O atoms and 2 moles of H atoms. 1 mole of water weighs 18 g and has 6.02 x 1023molecules

  11. For Ca(OH)2: 1 Ca = 40.1 amu 2 O = 32.0 amu 2 H = 2.0 amu 74.1 amu 1 mole of Ca(OH)2 has a mass of 74.1 g Ca(OH)2 is an ionic compound so we can’t talk about molecules. Sometimes the simplest formula – which indicates only the ratio of the ions – is referred to as a formula unit.

  12. How many atoms of O are there in 5.0 g of CO2?

More Related