VIEWS: 21 PAGES: 19 CATEGORY: Research POSTED ON: 11/4/2008 Public Domain
Review of Atomic Theory thus far Dalton (1766-1844) Thomson (1856-1940) Rutherford (1871-1937) Where are those electrons? Electron in Atoms 1 Bohr Model 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 Electron in Atoms 3 Quantum Mechanical Model Schrodinger’s 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 Electron in Atoms 4 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/ Electron in Atoms 5 Energy Levels/Orbitals 1st energy level 1 1S orbital 2nd energy level 1 2s, 3 2p’s 3rd energy level 1 3s, 3 3p’s, 5 3d’s 4th energy level 1 4s, 3 4p’s, 5 4d’s, 7 4f’s Electron in Atoms 6 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 Electron in Atoms 7 3 Rules of Guidance: Pauli exclusion principle Atomic orbital can only hold two electrons Electrons must be of opposite spin Hund’s rule Electrons will fill each orbital in a sublevel before pairing up to complete orbital Examples: B, F, any element! Tutorial Electron in Atoms 8 Exceptions to Electron Configurations Chromium Special stability with half filled orbitals Copper Special stability with full orbitals Electron configurations of ions? Try O2-, Na+ Electron in Atoms 9 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 Using Frequency, Wavelength, Speed of light equation Velocity, frequency, and wavelength c=λν 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? Electron in Atoms 11 Electromagnetic Spectrum Chart Electron in Atoms 12 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 Electron in Atoms 13 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 (Planck’s constant) Energy absorbed or emitted proportional to the frequency of radiation Electron in Atoms 14 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 Electron in Atoms 15 END Electron in Atoms 16 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 Electron in Atoms 17 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: Don’t let wooden splints burn more than necessary. Watch contamination. Lab Analysis Questions: All Electron in Atoms 18 de Broglie’s 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 Electron in Atoms 19