Have you ever wondered how you get different colored fireworks? Have you ever wondered how scientists know what stars are made of?
Bohr Model, Quantum Mechanics and the Electromagnetic Spectrum Let’s start with the basics!
I. Wave-Particle Duality Light behaves as both waves and particles Did you know light was made of particles?
A. Light as Waves Basic wave terminology Wavelength (λ, lambda): Distance between two crests of a wave. Measured in meters (m) Frequency (ѵ, nu): Number of wave cycles that pass a given point per second Measured in hertz, Hz. 1 Hz = 1/s = s-1 Amplitude: Height of wave
What is the relationship between wavelength and frequency? They are inversely proportional. ↑ ѵ, ↓ λ (increase frequency, decrease wavelength) ↓ ѵ, ↑ λ , (decrease frequency, increase wavelength)
The Electromagnetic Spectrum ↑ wavelength ↓ wavelength ↓ frequency ↑ frequency ↓energy ↑ energy
The Electromagnetic Spectrum Write in order from longest to shortest wavelength: radio, microwaves, radar, infrared, visible, ultraviolet, x-rays, gamma rays Write in order from highest to lowest frequency Gamma rays, x-rays, ultraviolet, visible, infrared, radar, microwaves, radio
B. Light as particles Energy is quantized – comes in discreet packets or quantities A quantum (particle) of light is called a photon
Putting it all together….seeing the light!
C. Bohr Model and the Electromagnetic Spectrum Let’s talk electrons again….
Ground state: Electron is occupying the lowest energy level possible Excited state: Electron is in a higher energy level than the ground state
How does an electron get excited (move up energy levels)? It must absorb a very specific amount (quantum) of energy. Where does that energy come from? Apply electricity Apply electromagnetic radiation (UV, light, x-ray, etc). EM radiation comes in photons, or packets of energy.
How it works…I see the light Electron in ground state Electron absorbs photons with a very specific amount of energy Energy causes electron to move to higher energy level Electron now in excited state Excited state = unstable atom Electron quickly falls back to ground state, emitting photon with same energy it originally absorbed. Wavelength/frequency of photon may be in visible spectrum If in visible spectrum, we will see corresponding colors
D. Emission and Absorption Spectra Emission Spectra Shows the wavelengths emitted by photons as electrons drop down to a lower energy level from a higher energy level (excited state) Every element has a unique emission spectrum—like a fingerprint.
Absorption Spectra Produced by atom absorbing photons of a specific wavelength
Why do Elements have Different Emission/Absorption Spectra? All atoms have energy levels, but the energy levels of each atom are different distances apart Different distances = different energies This means electrons of different atoms must absorb/emit photons of specific, but different energies to move up or down energy levels, so the absorption and emission spectra will be unique to each element.
Flame Test
http://video. google. com/videoplay http://video.google.com/videoplay?docid=-1150217790642063936&q=fireworks&hl=en http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/linesp16.swf http://www2.wwnorton.com/college/chemistry/gilbert/tutorials/ch3.htm