Review of Atomic Theory thus far

1
Review of Atomic Theory thus far

• Dalton (1766-1844)
• Thomson (1856-1940)
• Rutherford (1871-1937)
• Where are those electrons?

2
Bohr Model
3
Niels Bohr model (1885-1962)

• Electrons arranged in concentric circular orbits
  (planetary model)
• Levels hold different numbers of electrons
• 2, 8, 8 1st 3 levels
• Staircase, ladder analogies discrete energy
  levels
• Quantum energy required to move an electron
  from present level to next higher one
• Levels can be unequally spaced
• Higher the electron, steps become closer together

4
Quantum Mechanical Model

• Schrodingers model (1887-1961)
• Modern description of the electrons in atoms
  Quantum theory
• Restricts energy of electrons to certain values,
  but does NOT define specific orbits
• Estimates probability of finding electrons in
  certain positions
• Electron cloud model

5
Energy Levels and Atomic Orbitals

• Principal energy levels (n)
• Sublevels
• Atomic orbitals (each can hold 2 electrons)
• S, P, D, F
• What do Atomic Orbitals look like?
• http//www.shef.ac.uk/chemistry/orbitron/
• http//web.mit.edu/3.091/www/orbs/

6
Energy Levels/Orbitals

• 1st energy level
• 1 1S orbital
• 2nd energy level
• 1 2s, 3 2ps
• 3rd energy level
• 1 3s, 3 3ps, 5 3ds
• 4th energy level
• 1 4s, 3 4ps, 5 4ds, 7 4fs

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How do the electrons arrange themselves?

• Electron configurations
• Ways in which electrons are arranged around the
  nuclei of atoms
• 3 Rules of Guidance
• Aufbau principle
• Electrons enter orbitals of lowest energy first
• Show filling order

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3 Rules of Guidance

• Pauli exclusion principle
• Atomic orbital can only hold two electrons
• Electrons must be of opposite spin
• Hunds rule
• Electrons will fill each orbital in a sublevel
  before pairing up to complete orbital
• Examples B, F, any element!
• Tutorial

9
Exceptions to Electron Configurations

• Chromium
• Special stability with half filled orbitals
• Copper
• Special stability with full orbitals
• Electron configurations of ions?
• Try O2-, Na

10
Background for Quantum Theory

• Properties of Waves
• Crests, Troughs
• Amplitude (A)
• Height of the wave from origin to crest
• Wavelength (lambda)
• Distance between crests, troughs, or point
• Frequency
• Number of wave cycles to pass point per unit of
  time
• Units cycles per second hertz

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Using Frequency, Wavelength, Speed of light
equation

• Velocity, frequency, and wavelength
• c ? ?
• Frequency speed of light/wavelength
• Note relationships between variables-
  direct/indirect proportions
• Example
• frequency of yellow light 5.10 x 1014 Hz,
  calculate the wavelength.
• Example
• What is frequency of radiation whose wavelength
  is 5.00 x 10-6 cm?

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Electromagnetic Spectrum Chart
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Atomic Spectrum

• EM spectrum
• Radio waves, microwaves, visible light, infrared,
  UV light, X-rays, gamma rays
• Light as a continuous spectrum
• Light colors are different frequencies and
  wavelengths
• Sunlight through prism light separates into
  spectrum of colors
• ROYGBIV
• Many expecting continuous spectrum for atoms
• Instead, a line spectrum was observed
• Each element has a unique line spectrum

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Atomic Spectra

• Ground state configurations
• Excited state configurations
• Tutorial
• Energy emitted when electrons return from excited
  states
• E h v (energy of photons)
• h 6.62 x 10-34 J s (Plancks constant)
• Energy absorbed or emitted proportional to the
  frequency of radiation

15
Practice

• Also referred to as Photoelectric Effect
• What is energy of photon of microwave radiation
  whose frequency is 3.20 x 1011 s-1
• Calculate the energy (in Joules) of a photon
  whose frequency is 5.00 x 1015 s-1

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END
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Lab 2 A/W-3 Observing a Chemical Reaction

• Recording observations, differences between
  observations and interpretations, quantitative
  vs. qualitative observations
• Techniques Recording data real time
• Safety Goggles
• Lab Analysis Questions All except Design
  Experiment

18
Lab 3 A/W 20 Flame Tests

• Objectives
• Observe flame test for different metallic ions
• Identify an unknown metal using flame test
• Technique Notes
• Wooden splints instead of wire loops (No HCl)
• Unknown contains mixture of salts
• Safety Dont let wooden splints burn more than
  necessary. Watch contamination.
• Lab Analysis Questions All

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• de Broglies equation
• All matter exhibits wavelike motions
• Heisenberg uncertainty principle
• Impossible to know exactly both the velocity and
  the position of a particle at the same time