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Chapter 5: Electrons in Atoms Table of Contents • Chapter 5: Electrons in Atoms – 5.1: Light and Quantized Energy – 5.2: Quantum Theory and the Atom – 5.3: Electron Configuration REVIEW: History of the Atom Dalton Thomson All matter is made of tiny, indivisible atoms (demo) Plum pudding model Rutherford Positive nucleus and electrons in empty space around the nucleus REVIEW: History of the Atom • Bohr’s model and eventually the Electron Cloud model were developed in part to explain the different colors of light when elements burn 5.1 Light & Energy Wave Nature of Light • Light behaves like a wave –Wavelength (λ ) - distance between crests on wave (m) –Frequency (ʋ) – number of waves per second (Hz or 1/s or s-1) Light & Energy 5.1 Wave Nature of Light • Electromagnetic Radiation - energy with wavelike behavior. 2 parts: electric field and magnetic field Light & Energy 5.1 Wave Nature of Light • All electromagnetic waves travel at the speed of light (c): 3.00 x 108 m/s c = λν • c = speed of light (m/s) • λ = wavelength (m) • ν = frequency (/s or Hz) Light & Energy 5.1 Wave Nature of Light PRACTICE: c = λν • c = speed of light = 3.00 x 108 m/s • λ = wavelength = ??? • ν = frequency = 5.10 x 1014 /s c ÷ λ×ν λ = c/ν = 3.00 x 108 m/s ÷ 5.10 x 1014 /s = 5.88 x 10-7 m Light & Energy 5.1 Wave Nature of Light PRACTICE: c = λν • c = speed of light = 3.00 x 108 m/s • λ = wavelength = 2.50 x 10-6 m • ν = frequency = ?? c ÷ λ ×ν • ν = c/ λ = 3.00 x 108 m/s ÷ 2.50 x 10-6 m = 1.20 x 1014 /s 5.1 Light & Energy Electromagnetic Spectrum • Electromagnetic spectrum – the range of wavelengths of electromagnetic radiation • LIGHT: all wavelengths on the spectrum 5.1 Light & Energy Electromagnetic Spectrum • Electromagnetic spectrum – the range of wavelengths of electromagnetic radiation • LIGHT: all wavelengths on the spectrum 5.1 Light & Energy Sketch the EM Spectrum (use p. 120 in text) Light & Energy 5.1 Visible Light low energy high energy Red Orange Yellow Green Blue Indigo Violet White light is the combination of all the visible colors of light Light & Energy 5.1 Check • What are the two fields in electromagnetic radiation? electric field and magnetic field • Which EM radiation has the highest energy? – Gamma rays • Which has the lowest energy? – Radio waves • What are the colors of visible light? – ROYGBIV 5.1 Light & Energy Particle Nature of Light • Wave model doesn’t explain light’s interaction with matter. • Einstein proposed that light also behaves like a particle 5.1 Light & Energy Particle Nature of Light • When high frequency light hits metal, a photon is released. • Photon – particle of light energy 5.1 Light & Energy Emission Of Light • Quantum – minimum amount of energy that can be gained or lost by an atom; a packet of energy • Photon –carries a quantum of energy. 5.1 Light & Energy Electrons & Light • Bohr’s Model of the Atom: Electrons orbit the nucleus in fixed orbits around the nucleus. • Light (EM radiation): Caused when excited electrons “jump” from one energy level (orbital) and then return to original energy level (orbital) Light & Energy 5.1 Electrons & Light • As energy is absorbed, electrons move from their ground state (original energy level) to an excited state (higher energy level) Initial position ) ) nucleus ) ground state 1 2 energy levels ) 3 ) 4 Final position ) 5 ) excited state 6 7 Light & Energy 5.1 Electrons & Light • Electrons are unstable in their excited state, so they return to the ground state by releasing energy. During this return, light is emitted! Final position ) ) nucleus ) ground state 1 2 energy levels ) 3 ) 4 Initial position ) 5 ) excited state 6 7 5.1 Light & Energy Emission Of Light To calculate the energy in a photon: E = h· ν • Where – E = energy in Joules (J) – h = Planck’s constant 6.626 x 10-34 J·s – ν = frequency (Hz or /s) Light & Energy 5.1 Particle Nature of Light PRACTICE: E = h· ν h = Planck’s constant = 6.626 x 10-34 • E = energy = ??? • ν = frequency = 5.10 x 1014 /s E J·s h ÷ ×ν E = h x ν = 6.626 x 10-34 J·s x 5.10 x 1014 /s = 3.38 x 10-19 J Light & Energy 5.1 Particle Nature of Light PRACTICE: E = h· ν h = Planck’s constant = 6.626 x 10-34 • E = energy = ??? • ν = frequency = 7.23 x 1014 /s E J·s h ÷ ×ν E = h x ν = 6.626 x 10-34 J·s x 7.23 x 1014 /s = 4.79 x 10-19 J