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
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