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Chapter 4: Arrangement of Electrons in Atoms Chemistry

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Development of a New Atomic Model There were some problems with the Rutherford model…It did not answer: Where the e - were located in the space outside the nucleus Why the e - did not crash into the nucleus Why atoms produce spectra at specific wavelengths

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Properties of Light Wave-Particle Nature of Light – early 1900’s A Duel Nature It was discovered that light and e - both have wave-like and particle-like properties

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Wave Nature of Light Electromagnetic radiation – form of energy that exhibits wave-like behavior as it travels through space Electromagnetic spectrum Electromagnetic spectrum Electromagnetic spectrum All the forms of electromagnetic radiation Speed of light in a vacuum 3.0 x 10 8 m/s

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Wave Nature of Light Wavelength Wavelength Distance between two corresponding points on adjacent waves λλλλ nm Frequency Frequency Number of waves that pass a given point in a specified time νννν Hz - Hertz

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Wave Nature of Light Figure 4-1, page 92 Equation c=λν Indirectly related! Spectroscope Device that separates light into a spectrum that can be seen Diffraction Grating – the part of the spectroscope the separates the light

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Particle Nature of Light Quantum Minimum quantity of energy that can be lost or gained by an atom Equation E=hν Direct relationship between quanta and frequency Planck’s Constant (h) Planck’s Constant (h) Planck’s Constant (h) h=6.626 x 10 -34 Js

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Particle Nature of Light Photon Individual quantum of light; “packet” The Hydrogen Atom Line emission spectrum (Figure 4-5, page 95) Ground State Lowest energy state (closest to the nucleus) Excited State State of higher energy **When electron drops from its excited state to its ground state, a photon is emitted! This produces a bright-line spectrum. Each element has a characteristic bright-line spectrum – much like a fingerprint!**

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http://jersey.uoregon.edu/vlab/elements/Eleme nts.html http://jersey.uoregon.edu/vlab/elements/Eleme nts.html http://jersey.uoregon.edu/vlab/elements/Eleme nts.html

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Particle Nature of Light Why does an emission spectrum occur? Atoms get extra energy – voltage The e - jumps from ground state to excited state Atoms return to original energy, e - drops back down to ground state Continuous spectrum Continuous spectrum Continuous spectrum Emission of continuous range of frequencies

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Particle Nature of Light Bohr Model of the H atom 1913 – Danish physicist – Niels Bohr Single e - circled around nucleus in allowed paths or orbits e - has fixed E when in this orbit (lowest E closest to nucleus) Lot of empty space between nucleus and e - in which e - cannot be in space space E increases as e - moves to farther orbits orbits http://chemmovies.unl.edu/ChemAnime/BOHRQD/B OHRQD.html http://chemmovies.unl.edu/ChemAnime/BOHRQD/B OHRQD.html http://chemmovies.unl.edu/ChemAnime/BOHRQD/B OHRQD.html

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Particle Nature of Light Bohr Model (cont) ONLY explained atoms with one e - Therefore – only worked with hydrogen!!

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Particle Nature of Light Spectroscopy Study of light emitted by excited atoms Bright line spectrum

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The Quantum Model of the Atom e - act as both waves and particles!! De Broglie 1924 – French physicist e - may have a wave-particle nature Would explain why e - only had certain orbits Diffraction Bending of wave as it passes by edge of object Interference Occurs when waves overlap overlap

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The Quantum Model of the Atom Heisenberg Uncertainty Principle 1927 – German physicist It is impossible to determine simultaneously both the position and velocity of an e - 12:28-14:28

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The Quantum Model of the Atom Schrodinger Wave Equation 1926 – Austrian physicist Applies to all atoms, treats e - as waves Nucleus is surrounded by orbitals Laid foundation for modern quantum theory Orbital – main energy level; 3D region around nucleus in which an e - can be found Cannot pinpoint e - location!!

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Quantum Numbers Quantum Numbers Solutions to Schrodinger’s wave eqn Probability of finding an e - “address” of e - Four Quantum Numbers Principle Anglular Momentum Magnetic Spin

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Principle Quantum Number Which main energy level? (“orbital” “shell”) Symbol- n n is normally 1-7 (corresponds to period on periodic table) Higher the n, the greater the distance from the nucleus

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Angular Momentum Quantum Number What is the shape of the orbital? shape shape F shape F shape F shape Symbol – l l = s,p,d,f When n = 1, l = s n = 2, l = s,p n = 2, l = s,p n = 3, l = s,p,d n = 3, l = s,p,d n = 4, l = s,p,d,f n = 4, l = s,p,d,f http://www.chemeng.uiuc.edu/~alkgrp/mo/gk12 /quantum/ http://www.chemeng.uiuc.edu/~alkgrp/mo/gk12 /quantum/ http://www.chemeng.uiuc.edu/~alkgrp/mo/gk12 /quantum/

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Magnetic Quantum Number Orientation of orbital around nucleus Orientation Symbol – m s – 1 p – 3 p – 3 d – 5 d – 5 f – 7 f – 7 Every orientation can hold 2 e - !! Figures 4-13, 4-14, 4-15 on page 102-103

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Spin Quantum Number Each e - in one orbital must have opposite spins Symbol – s + ½, - ½ Two “allowed” values and corresponds to direction of spin

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Electron Configuration Electron configurations – arrangements of e - in atoms Rules: Aufbau Principle – an e - occupies the lowest energy first Hund’s Rule – each orbital is filled with 1e - first and then the 2 nd e - will fill Pauli Exclusion Principle – no 2 e - in the same atom can have the same set of QN 14:30-18:25

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Electron Configuration Representing electron configurations Use the periodic table to write! Know the s,p,d,f block and then let your fingers do the walking!

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Electron Configuration

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Representing Electron Configurations Three Notations Orbital Notation Electron Configuration Notation Electron Dot Notation

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Orbital Notation Uses a series of lines and arrows to represent electrons Examples

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Orbital Notation More examples

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Electron Configuration Notation Eliminates lines and arrows; adds superscripts to sublevels to represent electrons Long form examples

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Electron Configuration Notation Short form examples – “noble gas configuration”

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Electron Dot Notation Outer shell e - Inner shell e - Highest occupied energy level / highest principle quantum number Valence electrons – outermost e - Examples

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Electron Dot Notation More examples

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