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BOHR MODEL AND QUANTUM NUMBERS October 28, 2014 BOHR’S MODEL Why don’t the electrons fall into the nucleus? Move like planets around the sun. In circular orbits at different levels. Amounts of energy separate one level from another. When electrons are hit with energy (flame, heat) they jump to a different level. BOHR’S MODEL Nucleus Electron Orbit Energy Levels BOHR POSTULATED THAT: Fixed energy related to the orbit Electrons cannot exist between orbits The higher the energy level, the further it is away from the nucleus An atom with maximum number of electrons in the outermost orbital energy level is stable (unreactive) Increasing energy Fifth Fourth Third Second First Further away from the nucleus means more energy. There is no “in between” energy Energy Levels n= 1,2,3,4,5,6,7 HOW DID HE DEVELOP HIS THEORY? He used mathematics to explain the visible spectrum of hydrogen gas http://www.mhhe.com/physsci/chemis try/essentialchemistry/flash/linesp16. swf THE LINE SPECTRUM electricity passed through a gaseous element emits light at a certain wavelength Can be seen when passed through a prism Every gas has a unique pattern (color) LINE SPECTRUM OF VARIOUS ELEMENTS THE QUANTUM MECHANICAL MODEL Energy is quantized. It comes in chunks. A quantum is the amount of energy needed to move from one energy level to another. Since the energy of an atom is never “in between” there must be a quantum leap in energy. Schrödinger derived an equation that described the energy and position of the electrons in an atom ATOMIC ORBITALS Principal Quantum Number (n) = the energy level of the electron. Within each energy level the complex math of Schrödinger's equation describes several shapes. These are called atomic orbitals Regions where there is a high probability of finding an electron SUBLEVELS OF ENERGY s orbitals (sphere) p orbitals (dumbbell) d orbitals (5 dif ferent shapes) f orbitals (hard to visualize) SUBLEVELS, ORBITAL AND NUMBER OF ELECTRONS SUBLEVEL NUMBER OF ORBITALS S 1 p 3 d 5 f 7 To determine the number of electrons in a sublevel, we use the formula 2n 2 where “n” energy level that is outside of the nucleus. S ORBITALS 1 s orbital for every energy level 1s 2s 3s Spherical shaped Each s orbital can hold 2 electrons Called the 1s, 2s, 3s, etc.. orbitals P ORBITALS Start at the second energy level 3 different directions 3 different shapes Each orbital can hold 2 electrons The p Sublevel has 3 p orbitals THE D SUBLEVEL CONTAINS 5 D ORBITALS rd The D sublevel starts in the 3 energy level 5 different shapes (orbitals) Each orbital can hold 2 electrons THE F SUBLEVEL HAS 7 F ORBITALS The F sublevel starts in the fourth energy level The F sublevel has seven different shapes (orbitals) 2 electrons per orbital SUMMARY Starts at energy level Sublevel # of shapes (orbitals) Max # of electrons s 1 2 1 p 3 6 2 d 5 10 3 f 7 14 4 ELECTRON CONFIGURATIONS The way electrons are arranged in atoms. Aufbau principle- electrons enter the lowest energy first. This causes dif ficulties because of the overlap of orbitals of dif ferent energies. Pauli Exclusion Principle - at most 2 electrons per orbital dif ferent spins ELECTRON CONFIGURATIONS First Energy Level only s sublevel (1 s orbital) only 2 electrons 1s 2 Second Energy Level s and p sublevels (s and p orbitals are available) 2 in s, 6 in p 2s 2 2p 6 8 total electrons Third energy level s, p, and d orbitals 2 in s, 6 in p, and 10 in d 3s 2 3p 6 3d 10 18 total electrons Fourth energy level s,p,d, and f orbitals 2 in s, 6 in p, 10 in d, and 14 in f 4s 24p 6 4d 10 4f 14 32 total electrons GREAT SITE TO PRACTICE AND INSTANTLY SEE RESULTS FOR ELECTRON CONFIGURATION.