Chapter 4 Electron Configurations 4-1 Radiant energy 4-2 quantum theory 4-3 another look at the atom 4-4 a new approach to the atom 4-5 electron configurations
What do you see? Having several different images w/in one is as confusing as the mystery of electrons were to the scientists. There was no way to see them but they knew the electrons must be there Scientists just didn’t know what to do about them or what they specifically did
4-1 Radiant Energy What are the 4 characteristics of an electromagnetic wave? What are the major regions of the electromagnetic spectrum?
Light Most of what we know about how e- behave in atoms was learned from watching how light interacts w/ matter Light travels through space and is a form of radiant nrg
Nature of Light • The properties of light: • Properties of wave • Properties of particles
Waves • Light travels in waves like the ocean • These waves are electromagnetic wh. makes light a form of electromagnetic radiation • Electromagnetic radiation (x-rays, gamma rays, radio waves) • Electromagnetic waves have electric and magnetic fields oscillating at right angles to each other and to the direction of the motion of the wave
Waves • All waves can be described by 4 characteristics • Amplitude • Wavelength • Frequency • speed
Amplitude The height of the wave Determines the brightness/intensity
Wavelength Distance b/w wave crests The distance it takes for the wave to make 1 cycle Visible light has a wavelength b/w 400-750 nanometers
Frequency • Tells how fast the wave oscillates up and down • Measures how many cycles a wave makes in 1 second • Units: 1/s, s-1, 1 Hz • Radio stations broadcast at megahertz • 97.5 FM means the frequency of those radio waves are moving at 97.5 x 106 cycles per second • Visible light moves b/w 4 x 1014 – 7 x 1014 s-1
Speed of light • No matter the wavelength light moves at 3.00 x 108 m/s • b/c the speed does not change, relationships b/w wavelength and frequency can be made • The shorter the distance b/w the crests of a wave, the faster the wave oscillates up and down • The shorter the wavelength, the greater the frequency
λ = c/ν λ : wavelength c : speed of light – 3.00 x 108 ν : frequency If given the frequency of 4.74 x 1014 s-1, what would the wavelength be?
4-2 Quantum Theory What is meant by nrg quantization? How is the nrg of radiation related to its wavelength? How does the idea of photons of light explain the photoelectric effect?
???Unanswered questions??? • Why would metal radiate different wavelengths at different temperatures? • Start heating, no visible light Starts to glow red White hot • Why do different elements have different colors?
Planck’s Theory • Max Planck (1858-1947) • Proposed that there is a fundamental restriction on the amounts of nrg that an object emits/absorbs • Called these pieces of nrg quantum
Planck’s Theory • Quantum/quanta • Fixed amount • Goes against the previous theories of nrg
Planck’s Theory • E = hν • E = energy • h = 6.626 x 10-34 J-s • Unit: joule-second • ν = frequency
Planck’s Theory Using Planck’s theory, scientists can determine the temp of distant planets by measuring the λ of the electromagnetic radiation they emit
Planck’s Theory • Energies absorbed/emitted by atoms are quantized • Means their values are restricted to certain quantities • What would happen if a car’s nrg was quantized? • A car can only go so fast
Planck’s Theory • Look at figure 4-11 on pg 132 • In which direction would a person walk on the ramp/stairs to increase her potential nrg? • Up the ramp/stairs • Is there any location on the ramp that can’t be occupied during this increase? • No • How does a person’s movement on the stairs compare to a similar movement on the ramp? • To climb the stairs, a person can only occupy distinct levels/stairs • Would the motion of an elevator be continuous/not? Explain. • Yes, the motion is continuous, but people can only get off at certain levels.
Photoelectric Effect • Albert Einstein (1879-1955) • When light of a certain frequency is shone on some metals, the electrons of that metal will be emitted from the surface • These emitted e- are filled with nrg and can be used thereafter • Solar calculators • Camera light meters • Each metal has a minimum frequency of light to release e- • Example: sodium metal is not affected by red light no matter its intensity. A very faint violet light however will cause the e- to be emitted
Photoelectric Effect • Photons • Particles of EM radiation • No mass • Carry a quantum of nrg • nrg has certain minimum to cause ejection of photoelectron • Photon’s nrg must equal or exceed nrg needed to free an e- from an atom • nrg depends on frequency • Ephoton = hv
Photoelectric Effect • Photon strikes surface of metal • Photon transfers nrg to e- in metal atom • e- chooses to “swallow” whole photon • If swallowed, e- will use nrg to “jump” off the atom • The important, deciding factor is the ν of the photon not the # of photons • So why does violet light release e- but not red? • Violet has a greater ν, therefore a greater amount of nrg/photon
Photoelectric Effect • nrg of a photon explains effects of different kinds of EM radiation • Hospitals have signs warning that x-rays are being used • X-rays have high ν which means high nrg photons wh. could cause harm to living organisms • Radio waves surround us w/o any warning signs • Low ν, low nrg photons wh. don‘t harm organisms.
Photoelectric Cells Read the “Chemistry in Action” box on page 132
4-2 Section Review • p 134 (1-4) • What does it mean to say that nrg is quantized? • The nrg emitted/absorbed by any object is restricted to fixed amounts called quanta • How is the nrg of a quantum of radiant nrg related to its frequency? • The higher the frequency of light, the greater the nrg/photon • Why do you not ordinarily observe the quantization of nrg in the world around you? • Ea quantum of nrg is too small to notice in the everyday world • People who work around x-rays often wear film badges to monitor the amount of radiation to which they are exposed. Why do x-rays expose the film in the badge when other kinds of electromagnetic radiation do not? • X-rays have high frequencies. X-ray quanta have enough nrg to expose the film, whereas lower frequency waves do not.
Recap Video http://www.youtube.com/watch?v=_5F34NFWvL4
Group Activity • Each group will read their article • A PowerPoint will be made of the article information • The PowerPoint needs: • At least 5 slides • At least 2 pictures/diagrams • All members of the group presents
4-3 Another Look at the Atom What is a line spectrum? How does the Bohr model explain the line spectrum of hydrogen?
Line Spectra • A spectrum that only contains certain colors/wavelengths • Also called the atomic emission spectrum • A fingerprint of that particular element • Ea. element has its own color • Sodium had a yellow color in your flame test
Atomic Emission Spectra • The set of frequencies of EM waves emitted by atoms of a particular element • Explains neon signs • Each element has a unique spectrum and therefore can be identified within an unknown such as through a flame test • Your lab last Monday
Atomic Emission Spectrum • Not every color of the spectrum seen in an emission spectrum b/c not all frequencies of light are emitted
Why does it take more nrg for the painter to climb to the top rung of the ladder? The electrons of an atom occupy orbitals around the atom’s nucleus that are similar to the rungs of a ladder. The painter is moving farther away from Earth’s surface climbing to the top rung. For example, just as a person cannot step between the rungs of a ladder, an electron cannot occupy the space between the atom’s orbitals. Why does the paintbrush hit the ground with more energy when it falls from the top rung? Also, it takes energy for an electron to move from an orbital close to the atom’s nucleus to an orbital farther from the nucleus, just as it takes energy to move up the rungs of a ladder. The paintbrush had more potential energy at the top of the ladder.
The Bohr Model of the Hydrogen Atom • Niels Bohr (1885-1962) • Attended lecture of Rutherford and used his, Planck, and Einstein’s theories • Focused on Hydrogen • Simplest w/ only 1 e- • Using Rutherford’s “planetary orbit” model of e- around the nucleus, Bohr said that ea. “orbit” specified a certain quantum of nrg
The Bohr Model of the Hydrogen Atom • Bohr labeled ea. nrg level (orbit) w/ a quantum #, n • The lowest nrg level (closest to nucleus), called ground state • n = 1 • When the e- absorbs the right amount, it jumps to a higher nrg level • Called an excited state • Quantum #s: n=2, n=3, n=4, etc • Excited states represent larger orbits farther from the nucleus
The Bohr Model of the Hydrogen Atom • Physics 2000 • http://www.colorado.edu/physics/2000/quantumzone/bohr.html
Matter Waves • Movement of e- • We draw the orbitals as circles but the e- don’t actually move in a circle around the nucleus • e- move around as waves • Discovered by Louis de Broglie • 1924 • Physicist • French graduate student
Heisenberg’s Uncertainty Principle • If I put a balloon into a completely dark room, could you locate it without moving the balloon? • It is nearly impossible • Every time you touch the balloon it moves! • The e- is just like this
Heisenberg’s Uncertainty Principle Cont. • What if we put that same balloon in the dark room and gave you a flash light? Would you be able to find it now? • Yes, the tiny “photons” from the light reflect off the balloon & back into your eyes so that you see the balloon w/o having to touch it
Heisenberg’s Uncertainty Principle Cont. • When you hit the balloon w/ the photons, the balloon is so much bigger than the photons • When you hit an e- with a photon, the photon is the same size as the e- so they reflect off one another • After the “collision” the e- is now going in a different direction and is usually going much faster than before
Heisenberg’s Uncertainty Principle • States that there is no way to know exactly what an e- position and speed of an e- at any given time
Lasers Read the Chemistry in Action on p 140