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I. Waves & Particles (p ) Ch. 4 - Electrons in Atoms

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A. Waves zWavelength ( ) - length of one complete wave zFrequency ( ) - # of waves that pass a point during a certain time period yhertz (Hz) = 1/s zAmplitude (A) - distance from the origin to the trough or crest

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A. Waves A greater amplitude (intensity) greater frequency (color) crest origin trough A

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B. EM Spectrum LOWENERGYLOWENERGY HIGHENERGYHIGHENERGY

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LOWENERGYLOWENERGY HIGHENERGYHIGHENERGY ROYG.BIV redorangeyellowgreenblueindigoviolet

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B. EM Spectrum zFrequency & wavelength are inversely proportional c = c:speed of light ( m/s) :wavelength (m, nm, etc.) :frequency (Hz)

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B. EM Spectrum GIVEN: = ? = 434 nm = m c = m/s WORK : = c = m/s m = Hz zEX: Find the frequency of a photon with a wavelength of 434 nm.

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C. Quantum Theory zPlanck (1900) yObserved - emission of light from hot objects yConcluded - energy is emitted in small, specific amounts (quanta) yQuantum - minimum amount of energy change

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C. Quantum Theory zPlanck (1900) vs. Classical TheoryQuantum Theory

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C. Quantum Theory zEinstein (1905) yObserved - photoelectric effect

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C. Quantum Theory zEinstein (1905) yConcluded - light has properties of both waves and particles wave-particle duality yPhoton - particle of light that carries a quantum of energy

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C. Quantum Theory E:energy (J, joules) h:Plancks constant ( J·s) :frequency (Hz) E = h zThe energy of a photon is proportional to its frequency.

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C. Quantum Theory GIVEN: E = ? = Hz h = J·s WORK : E = h E = ( J·s ) ( Hz ) E = J zEX: Find the energy of a red photon with a frequency of Hz.

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II. Bohr Model of the Atom (p ) Ch. 4 - Electrons in Atoms

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A. Line-Emission Spectrum ground state excited state ENERGY IN PHOTON OUT

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B. Bohr Model ze - exist only in orbits with specific amounts of energy called energy levels zTherefore… ye - can only gain or lose certain amounts of energy yonly certain photons are produced

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B. Bohr Model zEnergy of photon depends on the difference in energy levels zBohrs calculated energies matched the IR, visible, and UV lines for the H atom

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C. Other Elements zEach element has a unique bright-line emission spectrum. yAtomic Fingerprint Helium zBohrs calculations only worked for hydrogen!

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C. Other Elements zExamples: yIron zNow, we can calculate for all elements and their electrons – next section

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III. Quantum Model of the Atom (p ) Ch. 4 - Electrons in Atoms

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A. Electrons as Waves zLouis de Broglie (1924) yApplied wave-particle theory to e - ye - exhibit wave properties EVIDENCE: DIFFRACTION PATTERNS ELECTRONS VISIBLE LIGHT

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B. Quantum Mechanics zHeisenberg Uncertainty Principle yImpossible to know both the velocity and position of an electron at the same time

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B. Quantum Mechanics zSchrödinger Wave Equation (1926) yfinite # of solutions quantized energy levels ydefines probability of finding an e -

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B. Quantum Mechanics Radial Distribution Curve Orbital zOrbital (electron cloud) yRegion in space where there is 90% probability of finding an e -

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C. Quantum Numbers UPPER LEVEL zFour Quantum Numbers: ySpecify the address of each electron in an atom

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C. Quantum Numbers 1. Principal Quantum Number ( n ) yMain energy level occupied the e- ySize of the orbital yn 2 = # of orbitals in the energy level

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C. Quantum Numbers s p d f 2. Angular Momentum Quantum # ( l ) yEnergy sublevel yShape of the orbital

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C. Quantum Numbers zn=# of sublevels per level zn 2 =# of orbitals per level zSublevel sets: 1 s, 3 p, 5 d, 7 f

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C. Quantum Numbers 3. Magnetic Quantum Number ( m l ) yOrientation of orbital around the nucleus Specifies the exact orbital within each sublevel

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C. Quantum Numbers pxpx pypy pzpz

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zOrbitals combine to form a spherical shape. 2s 2p z 2p y 2p x

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C. Quantum Numbers 4. Spin Quantum Number ( m s ) yElectron spin +½ or -½ yAn orbital can hold 2 electrons that spin in opposite directions.

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C. Quantum Numbers 1. Principal # 2. Ang. Mom. # 3. Magnetic # 4. Spin # energy level sublevel (s,p,d,f) orientation electron zPauli Exclusion Principle yNo two electrons in an atom can have the same 4 quantum numbers. yEach e - has a unique address:

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Feeling overwhelmed? Read Section 4-2!

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