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Isotopes

Isotopes. Of the Atom. Isotopes At the conclusion of our time together, you should be able to:. Define an isotope Determine the number of protons, neutrons and electrons for an isotope Define average atomic mass Determine the average atomic mass for an element given the isotopes.

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Isotopes

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  1. Isotopes Of the Atom

  2. IsotopesAt the conclusion of our time together, you should be able to: • Define an isotope • Determine the number of protons, neutrons and electrons for an isotope • Define average atomic mass • Determine the average atomic mass for an element given the isotopes

  3. Isotopes Atoms with the same number of protons & electrons but a different number of neutrons. They are the same element, are chemically identical and undergo the exact same chemical reactions They have different masses (different mass number). All isotopes are used to calculate average atomic mass (this mass is usually a decimal). Most elements consist of a mixture of isotopes.

  4. 11B 10B Isotopes • Atoms of the same element but different mass number. • Boron-10 (10B) has 5 p and 5 n • Boron-11 (11B) has 5 p and 6 n

  5. Two Isotopes of Sodium.

  6. Isotopes • According to international convention all atomic weights derive from the isotope carbon-12. • One atomic mass unit (amu) is exactly 1/12 of the mass of a C-12 atom. • The natural atomic mass of an element is the average of the atomic masses of the isotopes:

  7. 15 Helpful Hints On The Lab Report from Mr. T’s Vast Lab Experience!!! Hint #12. The probability of a given event occurring is inversely proportional to its desirability.

  8. Schematic Diagram of a Mass Spectrometer

  9. Neon Gas

  10. Mass Spectrum of Natural Copper

  11. Another Interesting Boat Name

  12. Determining Average Atomic Mass Because of the existence of isotopes, the mass of a collection of atoms has an average value. Boron is 20%10B and 80%11B. That is, 11B makes up 80% of the boron in the earth’s crust. For boron average atomic mass = 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu 11B 10B

  13. How to Determine Average Atomic Mass Determine Relative Abundance – % abundance divided by 100 Determine mass of each isotope and multiply relative abundance by this mass (keep all digits your calculator gives you) Determine Average Atomic Mass by adding up all the individual masses, round to “2” decimal places

  14. #1 Nitrogen Example • Because of the existence of isotopes, the mass of a collection of atoms has an average value. • 14N = 99% abundant and 15N = 1% • (0.99 x 14 amu) + (0.01 x 15 amu) = Avg. Atomic mass of N = ______________ Avg. Atomic mass of Sb = ______________ 14.01 amu 121.84 amu

  15. Average Atomic Mass Example Problem: There are three naturally occurring isotopes of neon: Ne-20, 90.51%, 19.99244 amu; Ne-21, 0.27%, 20.99395 amu; Ne-22, 9.22%, 21.99138 amu. Calculate the average atomic mass of neon. Atomic mass = (0.9051 x 19.99244 amu) + (0.0027 x 20.99395 amu) + (0.0922 x 21.99138 amu) Atomic mass = 18.10 amu + 0.057 amu + 2.03 amu = 20.18 amu

  16. Isotopes & Average Atomic Mass • Because of the existence of isotopes, the mass of a collection of atoms has an average value. • 6Li = 7.5% abundant and 7Li = 92.5% • Avg. Atomic mass of Li = ______________ • 28Si = 92.23%, 29Si = 4.67%, 30Si = 3.10% • Avg. Atomic mass of Si = ______________ 6.93 amu 28.11 amu

  17. Wish I’d of Thought of It!!!

  18. IsotopesLet’s see if you can: • Define an isotope • Determine the number of protons, neutrons and electrons for an isotope • Define average atomic mass • Determine the average atomic mass for an element given the isotopes

  19. Let’s see what you learned… Get your clickers ready!!!

  20. Isotopes? Which of the following represent isotopes of the same element? Which element? 234 X234 X235 X238 X 92939292 Uranium

  21. Self-Check Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12C 13C 14C 6 6 6 #p+ _______ _______ _______ #no _______ _______ _______ #e- _______ _______ _______ 6 6 6 7 8 6 6 6 6

  22. Self-Check Continued An atom has 14 protons and 20 neutrons. A. Its atomic number is a) 14 b) 6 c) 34 d) 20 B. Its mass number is a) 14 b)20 c) 16 d) 34 C. The element is a) Si b) Ca c) Se d) C D. Another isotope of this element is a) 34X b) 34X c) 36X 16 14 14

  23. Average Atomic Mass Practice Silicon has 3 isotopes with the following % abundances. Si-28, 92.23% Si-29, 4.67% Si-30, 3.10% Calculate silicon’s average atomic mass.

  24. Answer (28 amu x 0.9223) + (29 amu x 0.0467) + (30 amu x .031) = 28.11 amu

  25. Element “X” has three naturally occurring isotopes. 78.70% of “X” atoms exist as X-24, 10.03% exist as X-25 and 11.17% exist as X-26. What is the average atomic mass of element “X” in amu’s? • 24.00 • 24.29 • 24.30 • 24.99 • 25.00

  26. Candium Lab

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