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2011   core ib chemistry - topic 02
 

2011 core ib chemistry - topic 02

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    2011   core ib chemistry - topic 02 2011 core ib chemistry - topic 02 Presentation Transcript

    • IB Chemistry Power Points
      Topic 02
      Atomic Structure
      www.pedagogics.ca
      Atomic Structure
    • Review – Basic Atomic Structure
      POSITIVE
      NEUTRAL
      CHARGE
      CHARGE
      ATOM
      ATOM
      NUCLEUS
      ELECTRONS
      NUCLEUS
      ELECTRONS
      NEUTRONS
      PROTONS
      PROTONS
      NEUTRONS
      NEGATIVECHARGE
      POSITIVE CHARGE
    • Review – Basic Atomic Model
    • mass number A
      atomic number Z
      element symbol
      © Addison-Wesley Publishing Company, Inc.
      A-Z notation
      The atomic number equals the number of protons. Each element has a unique atomic number.
    • Mass Number
      © Addison-Wesley Publishing Company, Inc.
      mass number A = protons + neutrons
      • always a whole number
      • NOT the value given on the Periodic Table!
    • Practice: determine the required values and write the chemical symbol in A-Z notation.
      Chlorine-37
      atomic #:
      mass #:
      # of protons:
      # of electrons:
      # of neutrons:
      17
      37
      17
      17
      20
    • Ions
      • ions are electrically charged atoms
      Neutral atom
      gain electrons
      lose electrons
      positive ion
      negative ion
      p+ > e-
      p+ < e-
      cation
      anion
    • Practice: determine the required values for the negative chloride ion 37 Cl-1
      37 Cl-1
      atomic #:
      mass #:
      # of protons:
      # of electrons:
      # of neutrons:
      17
      37
      17
      18
      20
    • Practice: determine the required values for the positive calcium ion 40 Ca +2
      40 Ca+2
      atomic #:
      mass #:
      # of protons:
      # of electrons:
      # of neutrons:
      20
      40
      20
      18
      20
    • Isotopes: Atoms of the same element with different mass numbers.
      © Addison-Wesley Publishing Company, Inc.
      carbon-12 and carbon-14 are isotopes
      stable
      similar chemical properties
      radioactive
    • Radioisotopes and Their Uses
      Radioisotopes are unstable isotopes that undergo radioactive decay. Radioisotopes have a number of uses:
      U-235 is used as fuel in nuclear reactors
      Co-60 is used in cancer radiation therapy
      C-14 is used as a tracer and for archeological dating
      Am-241 is used in smoke detectors
    • Mass Spectrometer
      A mass spectrometer is used to detect, identify and measure the abundance of different atoms, molecules or molecular fragments.
      Mass spectrometer studies are used to determine the average atomic mass for an element. The operation of a mass spectrometer can be divided into 5 steps:
      Vaporization
      Ionization
      Acceleration
      Deflection
      Detection
    • Chapter 12
      13
      Vaporization: the element to be analyzed is heated and vaporized (gaseous form).
      =>
      http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
    • Chapter 12
      14
      Ionization: the gaseous element is injected slowly into a vacuum chamber where the atoms are bombarded by electrons. This forms ions positive ions X (g) + e- X+(g) + 2 e-
      =>
      http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
    • Chapter 12
      15
      Acceleration: the gaseous ions are accelerated through an electric field (towards a negative plate)
      =>
      http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
    • Chapter 12
      16
      Deflection: Ions are deflected in an adjustable magnetic field oriented at right angles to the path. Heavier ions are deflected less.
      =>
      http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
    • Chapter 12
      17
      Detection: ions of a specific mass are counted
      =>
      http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
    • A sample mass spectrograph
      Output provides the abundances of the elemental isotopes of different relative mass
    • Atomic Mass is Relative
      © Addison-Wesley Publishing Company, Inc.
      12C atom = 1.992 × 10-23 g
      • atomic mass unit (amu)
      • 1 amu = 1/12 the mass of a 12C atom
      • 1 p = 1.007276 amu1 n = 1.008665 amu1 e- = 0.0005486 amu
    • Average Atomic Mass
      Avg.
      Atomic
      Mass
      a weighted average of all isotopes of an element
      • based on the % abundance data from mass spectrometer
      • this value is found on the Periodic Table
    • Avg.
      Atomic
      Mass
      Average Atomic Mass
      EXAMPLE: Calculate the average atomic mass of chlorine if its abundance in nature is 75.77% 35Cl, and 24.23% 37Cl.
      35.48
      amu
    • Average Atomic Mass
      Gallium has two naturally occurring isotopes, Ga-69 and Ga-71, with masses of 68.9257 amu and 70.9249 amu, respectively. Calculate the percent abundances of these isotopes
      Average relative mass of Ga 69.7231 amu
      Solve to get 60.1% Ga-69 and 39.9% Ga-71
    • All EM radiation is fundamentally the same. The only difference between a gamma ray and a radio wave is the frequency/wavelength/energy.
    • White Light
      Prism
      Visible light is one category of EM radiation. The visible light spectrum is subdivided into six “colors”.
      RED
      ORANGE
      YELLOW
      GREEN
      BLUE
      VIOLET
    • A continuous spectrum includes all wavelengths of radiation in a given range.
      When white light is passed through a prism a continuous spectrum is produced.
    • Colored lights do not emit all the wavelengths of the visible light spectrum. For example, a red light emits mostly wavelengths from the red end of the spectrum.
      An energized gas sample will emit light of specific wavelengths characteristic of the gas. This is called a line spectrum
    • Emission spectra are unique for each element
    • The Bohr model of the atom was developed using information from hydrogen emission spectrum studies. Bohr envisioned an atomic model with:
      • a central dense positive nucleus composed of protons and neutrons.
      • negative electrons at specific energies orbit the nucleus
      • mostly empty space. Nucleus is 10-5 times smaller than atom.
    • Bohr further stated that the orbiting electrons occupy discrete energy levels. Electrons can only “jump” between energy levels if they absorb or emit a specific amount of energy.
    • Bohr saw the line spectrum of hydrogen as a direct result of energized electrons releasing a specific amount of energy by emitting a photon of light at a certain wavelength. The different lines in the hydrogen spectrum were evidence for a number of different energy levels.
    • higher energy
      shorter wavelength
      lower energy
      longer wavelength
      Visible spectrum for hydrogen atom
      convergence
    • Lower energy = more stable electron orbit
      Electrons fill the lowest energy orbitals first.
      Each orbital has a maximum possible number of electrons.As you should recall:
      1st energy level (ground state) = 2 electrons
      2ndenergy level = 8 electrons
      3rd energy level = 8 electrons
    • The electronic structure of an atom
      A carbon atom has six electrons
      1st energy level holds 2
      2nd energy level takes the remaining 4
      The electron structure for carbon would be written as 2,4
      The electrons in the outermost energy level are called valence electrons. Carbon has 4 valence electrons.
    • Try writing the electron structure for calcium
      A calcium atom has 20 electrons
      1st energy level holds 2
      2nd energy level holds 8
      3rd energy level holds 8
      4th energy level holds last 2
      The electron structure for calcium would be written as 2,8,8,2
    • Connect to Periodic Table
      EnergyLevel
      1
      2
      3
      4