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LECTURE Atomic Mass Mass Number Isotopes

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LECTURE  Atomic Mass Mass Number Isotopes Powered By Docstoc
					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)
The mass number is the number of
 protons and neutrons in a single
 atom (will be a whole number)
CALCULATING ATOMIC MASS
NUMBER
 Chlorinehas 2 naturally occurring
 isotopes: 35Cl and 37Cl. They are
 abundant at 75% and 25%, respectively.
 Calculate the atomic mass of Cl.
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?
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
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
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
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
MASS SPECTROMETER
A  mass spectrometer is an instrument
  which separates particles according to
  their masses.
 VAPORIZED
 IONIZED
 ACCELERATED
 DEFLECTED
 DETECTED
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.
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
 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
BALMER SERIES - HYDROGEN
APPLICATION PROBLEMS
Which  of the following are usually
 found in the nucleus of an atom?
  A.   Electrons and neutrons only.
  B.   Neutrons only.
  C.   Protons, neutrons, and electrons.
  D.   Protons and neutrons only.
APPLICATION PROBLEMS
The number    of neutrons in an atom
 of 135Ba is
  A.   56
  B.   82
  C.   138
  D.   194
APPLICATION PROBLEMS
How many electrons would have
about the same mass as a proton or a
neutron?
 A.   200
 B.   500
 C.   2000
 D.   5000
APPLICATION PROBLEMS
Which  one of the following is not a
 common use of a radioactive
 isotope?
  A.   As a fuel in fuel cells
  B.   Irradiating tumors in patients with
       cancer
  C.   Measuring the rate of uptake of a
       drug that has been swallowed
  D.   Finding the age of rocks
APPLICATION PROBLEMS
 Radioisotopes   of normally stable
 elements are
  A. Chemically extracted from the natural
     element
  B. Mined from scarce underground deposits
  C. Formed from the stable element in nuclear
     reactors
  D. Produced through chemical reactions of
     the stable element
APPLICATION PROBLEMS
 Identify   the following subatomic particles
  A.   The particle that has a much lower mass
       than the others ______________________
  B.   The particle that has no electrical charge
       ______
  C.   The particle that is not found in the nucleus
       ____________
  D.   The number of these in the nucleus is equal
       to the atomic number ___________
  E.   The particle that is gained or lost when ions
       form __________________

				
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posted:12/11/2012
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