ap chemistry atomic structure and periodicity chapter...
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Ch 7 AP notes part 1 201617.notebook
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Atomic Structure and PeriodicityChapter 7
AP Chemistry
Apr 198:53 AM
Electromagnetic radiation - electric and magnetic waves oscillating at right angles to each other and to the direction they travel
Ch 7 AP notes part 1 201617.notebook
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Electromagnetic Spectrum
Dec 201:35 PM
Characteristics of Waves
Wavelength ( ) - distance from crest of one wave to the crest of the next
Ch 7 AP notes part 1 201617.notebook
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Frequency ( )- the number of wave peaks that pass a given point per unit of time
Note that as wavelength increases, frequency decreases ( inverse relationship)
Oct 1711:27 AM
Ch 7 AP notes part 1 201617.notebook
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Speed of light in a vacuum (c) - all electromagnetic radiation travels at the same speed in a vacuum
2.9979 x 108 m/sc =
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How are these characteristics related?
Wavelength x frequency = speed of light
wavelength and frequency are inversely related
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spectral lines
White light when passed through prism makes a continuous spectrum
Light from a neon bulb with elemental gas makes a line spectrum
Which color of light has the longest wavelength?
Which color has the highest frequency?
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Concept check:1. Blue light has a shorter wavelength than red light.
2. Xrays have lower frequencies than radio waves.
3. Microwaves have higher frequencies than gamma rays.
4. Visible radiation composes the major portion of the electromagnetic spectrum
1 t, 2 f,3 f, 4 f
Oct 265:39 PM
Ex. Photosynthesis uses light with a frequency of 4.54 x 1014 s1. What wavelength does this correspond to?
Does this answer make sense?
visible
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Dec 202:29 PM
Light has measurable wave characteristics, so we know it travels as waves. However, in some ways light behaves as if it were streams of particles ( as in the photoelectric effect).
Therefore light has a dual nature We call this the wave-particle nature of light
Jan 1210:39 AM
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Early 20th century Light was thought of as waves, however there were 2 aspects of light that did not agree with the wave theory
1) Emission of light by matter when metal is heated, it first glows red, then yellow, then white known as “white hot”
problem with wave theory: wave theory predicted that extremely hot objects should emit infared, or invisible radiation
2) Absorption of light by matter
Photoelectric effect certain metals give off electrons when light of a certain frequency shines on them
problem with wave theory: only light of certain frequencies (or higher) can cause the metal to give off electrons. Wave theory predicts that all wavelengths should be able to produce the effect.
Ex. Intense red light can not produce the photoelectric effect, but dim violet light can.
Some History
Apr 239:43 AM
Max Planck proposed theory that eventually solved both problems by proposing that energy released or absorbed by objects is restricted to “pieces” or “ chunks” called quanta. (quantum singular)
proposed the equation relating the energy of a quantum to the frequency of
radiation it emits:
E = h vE energy h Planck’s constant 6.26 x 1034v frequency
The temperature of distant stars can be determined using Planck’s equation.(measuring the wavelength of light they give off, calculating the frequency from c=wavelength x frequency, then putting the frequency into Planck’s equation.)
Planck’s theory didn’t attract much attention at first.
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Einstein saw Planck’s idea as a new way to think of light.
--He used Planck’s theory to explain the problem with the
photoelectric effect.
--He proposed that light is made up of particles (called photons)
-different colors of light have different wavelengths, therefore have different frequencies. The higher the frequency, the higher the
energy.
This explains why the photoelectric effect works with violet light, but not with red. Red particles of light do not have enough energy ( frequency) to knock off electrons, violet particles do.
Photons
photoelectric effect
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Ch 7 AP notes part 1 201617.notebook
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Compton proved Einstein‛s theory by demonstrating that photons could collide with electrons producing an effect like that produced by a collision of marbles. ( known as the compton effect)
Oct 266:21 PM
E = h vE = change in energy for a system (in Joules PER PHOTON)
v= frequency of the wave (s1)h= Planck's constant (6.626 x 1034Js)
Only certain specific amounts of energy can be gained or lost in a substance. These quanta have magnitides that depend on the substance. Given the observed frequency change, the change in enery can be calculated for the absorption or emission of Photons (particles of light)
Ch 7 AP notes part 1 201617.notebook
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E = h v
Oct 278:35 AM
The Energy of a photonThe blue color in fireworks is often achieved by heating copper (I) chloride to about 1200 C. The the compound emits blue light having a wavelength of 450 nm. What is the increment of energy (the quantum) that is emitted at 450 nm by CuCl?
Therefore a sample of of CuCl emitting light at 450nm can lose energy only in increments of 4.41 x 1019 J, the size of the quantum in this case.
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Ex Sodium atoms have a characteristic yellow color when excited in a flame. The color comes from the emission of light of 589.0 nma. What is the frequency of this radiation?
b. what is the change in energy associated with this photon? Per mole of photons?
a.
This value is per photon. There are
Oct 266:41 PM
It takes 382 kJ of energy to remove one mole of electrons from gaseous cesium. What is the wavelength associated with this energy?Hint: the conversion between energy and wavelength requires the value of energy to be per photon. This is our first conversion.
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DeBroglie
--Reasoned that since light (waves) behaves like particles, electrons (particles of matter) should behave like waves ,
--referred to as “matter waves”
--Schrodinger carried out a mathematical analysis of De Broglie's idea that led to a new model of the Hydrogen that applies to all other atoms as well. (Bohr's model only worked for Hydrogen)
--This model is called the wave mechanical model
* ALL MOVING OBJECTS HAVE A WAVELENGTH*
Why can‛t we see the wavelength of moving objects??
-because the mass of an object has to be very small (like electrons) to have a wavelength long enough to observe
Oct 278:30 AM
Einstein derived the famous equation:
E=mc2 special theory of relativity
m = ERearranged it becomes:
Ephoton= hcc2
substitute E
m = c2
The apparent mass of a photon of light with a wavelength is given by:
de Broglie's Equation
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mvh= de Broglie's equation
Allows us to calculate the wavelength for a particle
v= velocity of moving object in m/s
h= Planck's Constant 6.626 x 1034 Js or kg/m2s2 s
m= mass in kilograms
Oct 271:09 PM
What is the wavelength of an electron (mass= 9.11 x 1031kg) traveling at 5.31 x 106 m/s?
Recall that 1 Joule = 1 kg m2/s2
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Line Spectra
All elements give off light of different colors when burned in a flame or when electric current is passed through them. Ex. fireworks, neon lights
This light is produced by the atom‛s electrons absorbing energy, then instantly releasing the energy in the form of light.
Dec 209:58 PM
This colored light contains only certain wavelengths (colors).
When this colored light is passed through a prism, it produces a line spectrum unique to that element
Line Spectrum
Continuous Spectrum
Line spectrum a spectrum that contains only certain colors.Continuous spectrum contains all colors. Ex. : rainbow
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The Bohr Model of The Hydrogen Atom
Why do elements give off their own characteristic wavelengths of light?
Neils Bohr proposed that electrons are allowed to have only certain orbits corresponding to different amounts of energy.
lowest energycalled ground state
higher energy called excited state
Bohr proposed that when an electron absorbs a quantum of energy, it jumps to an excited state, then immediately falls back to the ground state. It releases a photon of light as it falls.
Bohr was able to use Planck's equationE = h v
to predict the line spectrum of Hydrogenpowerful evidence in support of quantized energy levelsBohr’s model worked well only for hydrogen. However, this was an important step in the development
of present atomic theory (Quantum theory).
The energy it releases is equivalent to the difference in the two energy levels it falls between.
Apr 258:54 AM
2. As electrons fall back to ground state, they release a photon of light that corresponds to the frequency of color they produce.
Planck's equation
3. Bohr used Planck's equation to predict the line spectrum of Hydrogen
Line spectrum1. When electrons are excited, they absorb energy and jump out to an excited state, then immediately fall back to ground state.
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Each photon emitted by an
excited hydrogen atom corresponds to a particular
energy change in the hydrogen atom
Quantized energy levels of H
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The equation for Bohr's Model of the atom is
E = 2.178 x 1018 J Z2
n2( )E is the energy (in Joules)Z is the nuclear charge (1 for hydrogen's one proton)n is an integer related to orbital position. The farther out from the nucleus, the higher value of n. If an electron is given enough energy, it goes away from the nucleus, We say it ionized, and n=
The lowest energy state is n=1, the ground state
The highest energy state is n= , where an electron is ionized.
Not Required for AP Test (supposedly)
Ch 7 AP notes part 1 201617.notebook
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Example:Calculate the energy corresponding to the n=3 electronic state in the Bohr hydrogen atom.
For H, Z= 1 and in this problem, n=3
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Example #2 Calculate the energy change corresponding to the excitation of an electron from the n=1 to n=3 electronic state in the hydrogen atom.
Ch 7 AP notes part 1 201617.notebook
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What wavelength of electromagnetic radiation is associated with the energy change in promoting an electron from the n=1 to n=3 level in the hydrogen atom? ( use the value of E from the previous example)
Note: Even if E = ( as it will be when energy is released) you must assign a + value to wavelength because you cannot have a negative wavelength!
Not Required for AP Test
Oct 1810:22 AM
In the previous examples (Bohr model) the electrons do not escape the atom! ( because they are hit with photons in the visible specrtum which does not have enough energy to make them excape the atom)
In PES, they are hit with xrays or UV rays which actually knock them off.
Ch 7 AP notes part 1 201617.notebook
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Dec 205:23 PM
Heisenburg‛s Uncertainty Principle
-states that the position and momentum of a moving electron cannot simultaneous be measured and known exactly.
The very act of measuring it alters what you are trying to measure.
--to locate an electron, you have to strike it with a photon. The collision moves the electron in an unpredictable way.
Oct 1812:12 PM
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Dec 2011:21 PM
POGIL for PES
Oct 249:16 AM
Attachments
spectral lines
http://laserstars.org/data/elements/
photoelectric effect