Transcript Electromagnetic Radiation

Chapter 7
Atomic Structure
And
Periodicity
How Often Does The Topic Appear On AP Exam?
MC 10% of Questions
FR Almost Every Year
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Electromagnetic Radiation
Radiant energy that exhibits
wavelength-like behavior and
travels through space at the speed
of light in a vacuum.
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Waves
Waves have 3 primary characteristics:
1.
Wavelength: distance between two
peaks in a wave.
2.
Frequency: number of waves per
second that pass a given point in space.
3.
Speed: speed of light 3.00 X 108 m/s.
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Wavelength and frequency have an
inverse relationship.
 =c
λ = wavelength (in meters) lambda
ν = frequency (in cycles per second) nu
c = speed of light (m s-1)
Mnemonic Device: lambda nu charlie
The speed of light is 3.00 x
108
meter
second
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In the flame test lab Sr(NO3)2 produced a brilliant
magenta color light with a wavelength of around
6.50 x 102 nm. Calculate the frequency of the light.
Convert  = c
to  = c/Use
3.00 x 108 m/s for the speed of light
Don’t forget to change units to meters
1 nm = 109
8 m
3.0x10
Plug ‘n Chug
14 -2
n=
s = 4.62x10 s
-7
6.50x10 m
Do #32 p. 321
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Nature of Matter
Planck’s Constant
Planck’s Assumption: Transfer of energy is quantized,
and can only occur in discrete units, called quanta.
DE photon =
hc
l
E = change in energy, in J (kg x m2 / s2)
h = Planck’s constant, 6.63 X 10-34 J x s
m
-1
 = frequency, in cycle s
 = wavelength, in m
DE = h
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The Cu(NO3)2 used in our flame test lab
emitted a blue-green color having a
wavelength of 500 nm. What is the quantum
of energy emitted by the compound?
Steps to solving:
We know wavelength so use
to calculate frequency
Use DE = hn
To calculate the energy quantum emitted by
Cu(NO3)2
Time to Plug ‘n Chug
n=
c
l
m
3.0x10
-34
-19
s
DE = 6.63x10 J is
= 3.97x10 J
-7
5.00x10 m
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Tanning Beds?
Ultraviolet B radiation is in the wavelength range 280 to
320 nm. UV-B:
• triggers direct DNA damage which in turn induces an
increased melanin production
• is more likely to cause a sunburn than UVA as a result of
overexposure
• is thought to cause the formation of moles and some types
of skin cancer and causes skin aging (wrinkles before your
time)
A photon of UV light possess enough energy to mutate
a strand of human DNA. What is the energy of a
single UVB photon with a wavelength of 300 nm?
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Einstein & Photoelectric Effect
Electrons are emitted from metals when light of a
frequency (ν) above a specific threshold frequency
(ν0 ) strikes the surface.
Observed Characteristics:
No e- emitted ν < ν0
No e- emitted ν < ν0 , even if ↑ intensity
If ν > ν0 , e- ↑ w/ ↑ intensity
If ν > ν0 , KEe- ↑ linearly ↑ intensity
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Einstein & Photoelectric Effect
KEelectron = ½ mv2 = hν – hν0
•
•
•
•
•
m = mass of ev = velocity of ehν = energy of photon (Planck’s constant x frequency)
hν0 = threshold energy required to remove eDon’t confuse v (vee) for ν (nu)
Principle behind photocells in a camera light meter,
security lights, and auto-open doors 10
Energy and Mass
Energy has mass (Einstein said it 1st)
E =
2
mc
E = energy
m = mass
c = speed of light
Solve for Mass
m = E / c2
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Energy and Mass
DE photon =
hc
l
hc
E
h
l
mphoton= 2 = 2 =
lc
c
c
(Evidence for the dual nature of light.)
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Wavelength and Mass
de Broglie’s Equation
 = wavelength, in m
h
l=
mn
h = Planck’s constant, 6.63 X10-34 J x s = kg m2 s-1
m = mass, in kg
v = velocity
mv = momentum of electron
ALL particles exhibit a wave behavior. The equations allows us to
calculate the wavelength of a particle. See Sample Exercise 7.3
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Atomic Spectrum of Hydrogen p284
Continuous spectrum: Contains all the wavelengths
of light when white light is passed through a prism.
Line (discrete) spectrum: When one elements
emission spectrum is passed through a prism only
some of the wavelengths of light show up.
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The Bohr Model
Bohr proposed: electron in a hydrogen atom moves
around the nucleus only in certain allowed circular
orbits.
E  -2.178 x10
-18
Z 
J 2 
n 
2
E = energy of the levels in the H-atom
Z = nuclear charge (for H, z = 1)
n = an integer indicating the orbital of electron
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Transitions of Electrons
As electrons move
(transition) between
orbits, they give off
photons of light.
Moving from n=3 to
n=2 produces a red
photon.
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The Bohr Model
Ground State: The lowest possible
energy state for an atom (n = 1).
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Energy Changes in the Hydrogen
Atom
E = Efinal state - Einitial state
hc
l=
DE
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Quantum Mechanics
(a) Hydrogen electron is visualized as a standing wave around the
nucleus.
(b) Destructive interference will occur because the wave is not a
standing wave, ends are mismatched.
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Quantum Mechanics
Schrodinger’s Equation
Based on the wave properties of the atom
2


h
d
f
H


E

( H   E)   2
 V  x  f  E  f 
2
 8 m dx

 = wave function of coordinate x, y, & z (psi)
= mathematical operator
E = total energy of the atom
A specific wave function is often called an orbital.
Wave function is based on KE + PE = Total Energy
H
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Heisenberg Uncertainty Principle
h
 x    mv  
4
∆x = uncertainty in position of electron
∆mv = uncertainty in momentum (p) of electron
h = Planck’s constant
The more accurately we know a particle’s position, the less
accurately we can know its momentum.
The limitation are very small if you are using large objects like
baseball but for small objects the limitations are greatly
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magnified.
Probability Distribution p292
é
ëy (x1 iy1 iz1 ) ù
û = N1
2
N2
é
ù
y
(x
iy
iz
)
2
2
2 û
ë
2
 square
of the wave function indicates the
probability of finding an electron at a given
position, the model does not tell us when it will be
at that position (fig 7.11a)
Radial probability distribution is the probability
distribution in each spherical shell (fig7.11b)
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Quantum Numbers (QN)
Principal QN (n = 1, 2, 3, . . .) - related to size and
energy of the orbital. Electron requires more
energy to exist further from nucleus.
Angular Momentum QN (l = 0 to n -1) - relates to
shape of the orbital. l=0 (spherical), l=1 (polar), l=2
(cloverleaf).
Magnetic QN (ml = l to - l) - relates to orientation
of the orbital in space relative to other orbitals.
Electron Spin QN (ms = +1/2, -1/2) - relates to the
spin states of the electrons.
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Quantum Numbers
Value of l
Letter Used
Number of
Orbitals
0
s
1
1
p
3
2
d
5
3
f
7
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Orbitals correspond to blocks on Periodic Table
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Orbital Shapes
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Pauli Exclusion Principle
•
In a given atom, no two electrons can have the
same set of four quantum numbers (n, l, ml, ms).
•
Therefore, an orbital can hold only two
electrons, and they must have opposite spins.
If 2 electrons in outer most orbital – substance is diamagnetic
If 1 electron in outer most orbital – substance is paramagnetic
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History of Periodic Table
Johann Dobereiner – 1829 - found several groups of 3
(triads)
John Newland – 1864 – elements arranged in octaves
Lothar Meyer & Dimitri Mendeleev -1872 –
independently produced periodic table based on
mass of elements. Mendeleev given most credit
because of its predictive ability.
Henry Moseley – 1913 – arranged table in increasing
atomic number – today’s version
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Aufbau Principle
•
Electrons are added one by one to
elements from the inner most orbital to
the outer most orbital.
• Aufbau is German for “building up”
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Hund’s Rule
•
The lowest energy configuration for
an atom is the one having the
maximum number of unpaired
electrons in a particular set of orbitals.
• Ex. - The rule says you will put an
electron in each p orbital BEFORE you
pair them up.
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Valence Electrons
The electrons in the highest principle quantum level
of an atom.
Valence
Configuration Elem.
Electrons
2
[Ar] 4s
Ca
2
2
3
N
5
2
5
Br
7
[He] 2s 2p
[Ar] 4s 4p
Inner electrons are called core electrons.
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Periodic Table Classifications p307
Representative Elements (main group): filling s and
p orbitals (Na, Al, Ne, O)
Transition Elements: filling d orbitals (Fe, Co, Ni)
Lanthanide and Actinide Series (inner transition
elements): filling 4f and 5f orbitals (Eu, Am, Es)
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Ionization Energy
The quantity of energy required
to remove an electron from the
gaseous atom or ion.
X( g) ® X
+
( g)
+e
-
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Periodic Trends
First Ionization Energy
increases from left to right across a
period ( A# means nuclear attract.)
decreases going down a group (shielding
effect)
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Electron Affinity
The energy change associated with the
addition of an electron to a gaseous
atom.
-
X( g) + e ® X
-1
( g)
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Periodic Trends
Atomic Radii
Measure the distance between atoms in
chemical compounds.
decrease going from left to right across a period
(nuclear attraction)
increase going down a group (shielding effect)
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Information Contained in the
Periodic Table
1.
Each group/family member has the same valence
electron configuration (these electrons primarily determine
an atom’s chemistry).
2.
Should know the electron configuration of any
representative element.
3.
Certain groups have special names (alkali
metals, halogens, etc).
4.
Metals and nonmetals are characterized by their
chemical and physical properties.
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