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Counting Atoms

Counting Atoms. 1. 2. Atomic Symbol. 15.9994. O. Average Atomic Mass Elemental Symbol Atomic Number Element Name Mass Number. 8. OXYGEN. O. 16. 8. Oxygen-16. So What is the…. Average Atomic Mass ??

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Counting Atoms

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  1. Counting Atoms 1 2

  2. Atomic Symbol 15.9994 O • Average Atomic Mass • Elemental Symbol • Atomic Number • Element Name • Mass Number 8 OXYGEN O 16 8 Oxygen-16

  3. So What is the… • Average Atomic Mass ?? • The weighted avg. of the atomic masses of the naturally occurring isotopes of the element • Atomic Number ?? • The nbr. of protons in the nucleus • Elemental Symbol ?? • One or two letter symbol given to element, based on name • Mass Number ?? • The total nbr. of protons and neutrons in the nucleus of an isotope

  4. Are You Neutral? • All atoms, unless otherwise noted, are neutral. Meaning that they have the same number of _______ as ________. • Protons • Electrons • Remember that the nbr. of p+ is equal to the atomic nbr. • Every element has a specific atomic nbr., no two element have the same A.N.

  5. Put It All Together!!! • Remember that the mass nbr. is equal to M.N. = (p+) + (n0) • What is the atomic nbr. of Chlorine (Cl)? • How many p+ are there? How many e-? • If the mass nbr. is 37 (Chlorine-37). How many n0 are there? 17 17 17 10

  6. Try this… • Determine the number of protons, neutrons and electrons in an atom of each of the following: Carbon-14 Uraniuim-234

  7. Isotopes • Atoms of the same element the have different masses • A modification to Dalton’s original Atomic Theory • Nuclide – a general term for any isotope

  8. Try this… • Hydrogen has three isotopes/nuclides, Hydrogen-1 (Protium), Hydrogen-2 (Deuterium) and Hydrogen-3 (Tritium) • Diagram a model showing the number and location of protons (p+), Neutrons (n0) and electrons (e-) 1 H 1 2 H 1 3 H 1

  9. How do we determine the Avg. Atomic Mass? • How do you determine your grade for this class. • Its based on percentages. • Tests/Homework/Participations… every category doesn’t carry the same weight! • It’s a weighted average! • The same idea applies to calculating Avg. Atomic Masses.

  10. Each isotope has its own percentage or abundance • How much is naturally occurring • Each isotope has its own atomic mass • When calculating the average atomic mass, you use the atomic mass of the isotopes NOT the mass number • The atomic mass is measured in amu’s (atomic mass units) • 1amu = 1/12 the mass of the carbon-12 atom or 1.660540 x 10-27 g

  11. Try this… • Oxygen has three isotopes… Isotopemass (amu)abundance Oxygen-16 15.995 99.762 Oxygen-17 16.999 0.03800 Oxygen-18 17.999 0.2000 Calculate the average atomic mass of oxygen. Round the avg. atomic mass to the least accurate measurement.

  12. IONS • Take it Mr. F

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