2016 Topic 2: Atomic Structure
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This document discusses atomic structure and properties. It begins by reviewing the basic atomic model including protons, neutrons, and electrons. It then discusses atomic number, mass number, isotopes, ions, and electron configuration. The document also covers average atomic mass and mass spectrometry. It concludes by discussing the Bohr model of the atom and how this helped explain emission spectra of elements. In summary, the key topics covered are the fundamental particles of atoms, atomic notation, isotopes, ions, electron configuration, and early atomic structure models.
2016 Topic 2: Atomic Structure
- 1. Atomic Structure IB Chemistry Power Points Topic 02 Atomic Structure www.pedagogics.ca
- 2. Review – Basic Atomic Structure ELECTRONS ELECTRONS NEUTRONS NEUTRONS PROTONS POSITIVE CHARGE ATOM POSITIVE CHARGE NEUTRAL CHARGE NUCLEUS NEGATIVE CHARGE
- 3. Review – Basic Atomic Model Subatomic components Relative Mass Charge Proton 1 +1 Neutron 1 0 Electron 5 x 10-4 -1
- 4. A-Z notation element symbol © Addison-Wesley Publishing Company, Inc. 12 6C mass number A atomic number Z The atomic number equals the number of protons. Each element has a unique atomic number.
- 5. Mass Number • mass number A = protons + neutrons • always a whole number • NOT the value given on the Periodic Table! © Addison-Wesley Publishing Company, Inc.
- 6. 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 Cl 37 17
- 7. Ions • ions are electrically charged atoms Neutral atom lose electrons gain electrons positive ion negative ion p+ > e- p+ < e-cation anion
- 8. 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
- 9. 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
- 10. 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
- 11. 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
- 12. 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: 1. Vaporization 2. Ionization 3. Acceleration 4. Deflection 5. Detection
- 13. Vaporization: the element to be analyzed is heated and vaporized (gaseous form). Chapter 12 13=> http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
- 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 Chapter 12 14=> http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
- 15. Acceleration: the gaseous ions are accelerated through an electric field (towards a negative plate) Chapter 12 15=> http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
- 16. Deflection: Ions are deflected in an adjustable magnetic field oriented at right angles to the path. Heavier ions are deflected less. Chapter 12 16=> http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
- 17. Detection: ions of a specific mass are counted Chapter 12 17=> http://www.magnet.fsu.edu/education/tutorials/java/singlesector2/index.html
- 18. A sample mass spectrograph Output provides the abundances of the elemental isotopes of different relative mass
- 19. Atomic Mass is Relative • 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 amu 1 n = 1.008665 amu 1 e- = 0.0005486 amu © Addison-Wesley Publishing Company, Inc.
- 20. Average Relative Atomic Mass AR • 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 (mass)(%) (mass)(%) 100 Avg. Atomic Mass
- 21. Average Relative Atomic Mass AR • EXAMPLE: Calculate the average atomic mass of chlorine if its abundance in nature is 75.77% 35Cl, and 24.23% 37Cl. Avg. Atomic Mass (35)(75.77) (37)(24.23) 100 35.48 amu
- 22. Average Relative Atomic Mass AR 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 equation 1 equation 2 (68.9257)(x) (70.9249)(y) 69.7231= 100 x + y = 100 Solve to get 60.1% Ga-69 and 39.9% Ga-71
- 24. All EM radiation is fundamentally the same. The only difference between a gamma ray and a radio wave is the frequency/wavelength/energy.
- 25. Visible light is one category of EM radiation. The visible light spectrum is subdivided into six “colors”. White Light Prism RED ORANGE YELLOW GREEN BLUE VIOLET
- 26. 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.
- 27. 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
- 28. Emission spectra are unique for each element Balmer Lyman
- 30. 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.
- 31. 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.
- 32. 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.
- 33. lower energy longer wavelength higher energy shorter wavelength Visible spectrum for hydrogen atom convergence
- 34. Lower energy = more stable electron orbit Electrons will first occupy the lowest energy level orbital (Aufbau principle). Each energy level has a maximum possible number of electrons. As you should recall: 1st energy level (ground state) = 2 electrons 2nd energy level = 8 electrons 3rd energy level = 8 electrons
- 35. A carbon atom has six electrons 1st energy level holds 2 2nd energy level takes the remaining 4 The electron configuration for carbon would be written as 2,4 The electrons in the outermost energy level are called valence electrons. Carbon has 4 valence electrons.
- 36. Try writing the electron configuration 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 configuration for calcium would be written as 2,8,8,2
- 37. Connect to Periodic Table Energy Level 1 2 3 4