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Atomic Mass, Mass Number

LECTURE: Atomic Mass/Mass Number Isotopes Radioactive Isotopes Mass Spectrometer Hydrogen Spectrum. Atomic Mass, Mass Number. The atomic mass number is the AVERAGE of all the isotopes of an element ( will be a decimal number )

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Atomic Mass, Mass Number

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  1. LECTURE: Atomic Mass/Mass NumberIsotopesRadioactive IsotopesMass SpectrometerHydrogen Spectrum

  2. Atomic Mass, Mass Number • The atomic mass number is the AVERAGE of all the isotopes of an element (will be a decimal number) • The mass number is the number of protons and neutrons in a single atom (will be a whole number)

  3. Calculating Atomic Mass Number • Chlorine has 2 naturally occurring isotopes: 35Cl and 37Cl. They are abundant at 75% and 25%, respectively. Calculate the atomic mass of Cl.

  4. Calculating % Abundance from Atomic Mass of Known Isotopes • Iridium is composed of almost entirely 191Ir and 193Ir. Its molar mass is 192.2 g mol-1. What are the naturally occurring percentages of the two isotopes?

  5. Radioactive Isotopes • Radioactive isotopes of all elements can be produced by exposing the natural element to a flux of slow-moving neutrons in a nuclear reactor; the nucleus captures neutrons

  6. USES OF “RADIOISOTOPES” • CARBON-14 DATING • C-14 is found in all living things due to the exchange occurring in the carbon cycle • When an organism dies, the C-14 proportion stops and begins to decay • Half-Life = 5,700 years

  7. USES OF “RADIOISOTOPES” • TRACERS • Radioisotopes can be used biologically • Ex. Iodine radioisotopes can be ingested (drank) to measure the activity of the thyroid gland (which absorbs iodine) • The increase in radioactivity of the gland is then measured

  8. USES OF “RADIOISOTOPES” • INTENSE RADIATION • Some radioisotopes produce intense radioactivity (gamma rays) • EX. Co-60; which is used in radiation treatment or industrially to monitor the thickness of a steel plate from a rolling mill

  9. Mass Spectrometer • A mass spectrometer is an instrument which separates particles according to their masses. • VAPORIZED • IONIZED • ACCELERATED • DEFLECTED • DETECTED

  10. Electromagnetic Spectrum • The study of the emission of light by atoms and ions is the most effective technique for deducing the electronic structure of atoms. • The best evidence that electrons in an atoms surround the nucleus in certain allowed energy levels, or orbitals, comes from a study of the emission spectra of elements.

  11. Electromagnetic Spectrum • Remember the flame test???? • Excited electrons will absorb energy and jump to higher energy levels. • To return to ground state, they will emit light energy of a characteristic color. • Ex. • Lithium – RED • Sodium - YELLOW

  12. Electromagnetic Spectrum • Energy levels are not evenly spaced, so as the wavelength gets shorter (and frequency gets higher) the lines in the spectrum will converge

  13. BALMER SERIES - Hydrogen

  14. APPLICATION PROBLEMS • Which of the following are usually found in the nucleus of an atom? • Electrons and neutrons only. • Neutrons only. • Protons, neutrons, and electrons. • Protons and neutrons only.

  15. APPLICATION PROBLEMS • The number of neutrons in an atom of 135Ba is • 56 • 82 • 138 • 194

  16. APPLICATION PROBLEMS • How many electrons would have about the same mass as a proton or a neutron? • 200 • 500 • 2000 • 5000

  17. APPLICATION PROBLEMS • Which one of the following is not a common use of a radioactive isotope? • As a fuel in fuel cells • Irradiating tumors in patients with cancer • Measuring the rate of uptake of a drug that has been swallowed • Finding the age of rocks

  18. APPLICATION PROBLEMS • Radioisotopes of normally stable elements are • Chemically extracted from the natural element • Mined from scarce underground deposits • Formed from the stable element in nuclear reactors • Produced through chemical reactions of the stable element

  19. APPLICATION PROBLEMS • Identify the following subatomic particles • The particle that has a much lower mass than the others ______________________ • The particle that has no electrical charge ______ • The particle that is not found in the nucleus ____________ • The number of these in the nucleus is equal to the atomic number ___________ • The particle that is gained or lost when ions form __________________

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