quicktime movie on flame tests

quicktime
movie on
flame tests
Flame tests
• elements/monatomic ions give unique colors if
they are placed in a flame
Symbol
Name
Color
As
Arsenic
Blue
B
Boron
Bright Green
Ba
Barium
Pale/Apple Green
Ca
Calcium
Orange to Red
Cs
Caesium
Blue
Cu(I)
Copper(I)
Blue
Cu(II)
Copper(II) (non-halide)
Green
Cu(II)
Copper(II) (halide)
Blue-green
Fe
Iron
Gold
In
Indium
Blue
K
Potassium
Lilac
Robert Bunsen
discharge tubes
• gases in glass tubes will conduct
electricity if very high voltage is applied
• when they do this they emit light
• different gases give different colors
“neon” signs are
discharge tubes
helium = pink
mercury = light blue
neon = reddish-orange
argon = lavender
xenon = white
1
prism separates white light into Roy G. Biv
white light includes sunlight, fluorescent, and incandescent bulbs.
V
I
B
G
Y
O
Red
Orange
Yellow
Green
Blue
Indigo
Violet
R
white light is combination of all colors of the rainbow
white
light source
Line Spectra
line sp
ectru
m
Robert Bunsen
or
light
different line spectra for every
element like a unique fingerprint
more line spectra
line spectra can be detected from space
telling us about the elements in stars
2
properties of waves
wait, why are we studying this?
light is a wave
take a snapshot of a wave
wavelength distance between high points
amplitude is height of wave
these waves have
different amplitudes
λ
λ
but the same wavelength
this waves wavelength
is ½ the wavelength of
the wave above
wavelength/frequency
both describe
the same wave
distance between high
points in a snapshot of a
wave is the wavelength
1/time between high
points is the frequency
frequency
• given the greek symbol ν (nu)
• be careful not to confuse it
with velocity v
• units of cycles per second
• also written just s-1
1 cycle
second
Heinrich Hertz
= 1 Hertz or (Hz)
3
units of wavelength and frequency
wavelength x frequency = velocity
this is the speed
the wave is
going forward
meters cycles
x
= meters
cycle second
second
true for all kinds of waves sound, water etc.
νλ = c
speed of light is 2.99 x 108 m/s
given symbol c
light is a wave
• many types of “light” we cannot see
• all light is called electromagnetic radiation
• speed light is c = 2.99 x 108 m/s
aka visible spectrum
electromagnetic spectrum
4
converting frequency and wavelength
junction
νλ = c
destination
home station
• for light c is a constant
• if we know ν or λ we can calculate the other
• remember ν and λ both describe the same wave
just different ways to describe it
converting frequency
wavelength
wavelength
length of 1 cycle
λ
wavelength
λ=
c
ν
ν=
c
λ
frequency
ν
time for 1 cycle
frequency
why do we have to call it
electromagnetic radiation?
opposite charges
attracted
e-
+
+
-
-
like charges repelled
e-
• water waves amplitude? height
• sound waves amplitude? pressure
• electromagnetic waves amplitude?
strength of force felt by charged object
and/or a magnet
5
energy
of light
• all waves have energy
- water waves PE gravity and KE
- sound waves kinetic energy that
creates the pressure
• light is different from other kinds of
waves
• its energy is transferred in packets called
photons
• photons are particles
Planck’s Formula
• energy of a photon of light Ephoton= hν
• h = Planck’s constant 6.62 x 10-34 J*s
• the smallest amount of energy
the light wave can transfer
• like the penny of energy for
this frequency of light
• also written Ephoton= hc/λ
Max Planck
dunking tank an analogy for photons in action
if the baseball hits the target hard
enough the girl gets dunked
6
photons and DNA damage
• like the dunking tank
• if photon hits the DNA and has enough
energy
the DNA can be broken
ible light does
not damage
• visible light does not have enough energy
• UV light (λ less than 400 nm) has enough
energy 650
light
350nm
nmred
(UV)
light
ed
ag
m
da
DN
A
DNA
photons and DNA damage
ou
en
e A
av N
t hNAe D
ndo Dag
esge m
dmoa da
hdta to
lig y
e erg
bl
si en
vi
• like the dunking tank
• if photon hits the DNA and has enough
energy the DNA can be broken
• visible light does not have enough energy
• UV light (λ less than 400 nm) has enough
energy 350
650nm
nm(UV)
red light
light
DNA
gh
quicktime
movie on
photoelectric
effect
7
sunglasses
• materials that block UV
light are abundant and
cheap
• most plastics block UV
• materials that do not
block UV light are
relatively rare and costly
• cheap sunglasses are
functional
8
Line Spectrum
of Hydrogen
highest
energy
energy of electrons in atoms organized like a building
each line is like a ball thrown from a different floor
highest
only certain potential energies energy
b/c floors only at certain heights
434 nm
every line is a different wavelength
every wavelength is a different
energy that is being released
wavelength (nm)
486 nm
E = hc
λ
E=
lower
energy
lower
energy
lowest
energy
6.626 x 10-34 J*s x 2.99 x108 m/s
486 x10-9 m
= 4.076 x 10–19 J
heat (q)
released
energy of a
486 nm photon
656 nm
lowest
energy
Bohr Model of Hydrogen
etc.
n=5
n=3
n=4
n=2
n=1
nucleus
Niels Bohr
electron
• electron can be in different orbits
-like planets in a solar system
• each orbit has a quantum number n
9
Bohr Model of Hydrogen
the electron has a
different potential energy in
each orbit b/c it is a different
distance from the nucleus
each bowling ball has
a different potential
energy b/c it is a different
distance from the earth
higher
potential
energy
higher
potential
energy
electrons
nucleus
attraction of positive nucleus/negative electrons
like gravity attracting you or a bowling ball to earth
gravity makes objects at higher
height have higher potential energy
Bohr Model of Hydrogen
• electron in hydrogen is at certain energy levels called orbits
• quantum number n counts the orbits
-like floors in a building
higher potential energy
• a single photon emitted when electrons move to lower floors
- like the heat released when bowling ball hits ground
• energy of the different lines in the line spectrum
described by a formula
1
1
∆E = RH ( n 2 - n 2 )
f
i
where RH is the Rydberg constant, 2.18 × 10 18 J
ni and nf are the initial and final energy levels of the electron.
Example: What is the difference in energy
when an electron goes from the n=3 to n=2
energy level of hydrogen?
1
1
∆E = RH ( n 2 - n 2 )
f
i
∆E = -2.18 x 10-18 (1/32 -1/22) = 3.02x10-19 J
What wavelength of light is emitted when the electrons
goes from n = 3 to the n = 2 energy level in hydrogen?
Ephoton = energy difference between n=3 and n=2
Ephoton = hc
λ
= 3.02x10-19
3.02 x 10-19 J =
λ=
6.626 x 10-34 J*s x 2.99 x 108 m/s
λ
6.626 x 10-34 J*s x 2.99 x 108 m/s
3.02x10-19 J
= 6.56 x10-7 m
or 656 nm
10
diffraction
when waves collide with objects
or try to pass through openings
close to their wavelength
they undergo diffraction
opening close to size of
wavelength of the wave
diffraction!
opening wave bumps into
as it tries to pass through
d’Oh!!!
wave
for visible light a pinhole
will cause some diffraction
if the wave happens to be light then diffraction
spreads it out magnifying the image
class demo in pinhole diffraction
1. take a pin and make the smallest hole you can
in a piece of aluminum foil
2. hold the foil up to the light and try to view the
tip of the pin through the hole
3. after you see the pin move the foil out of your
line of sight and try to continue viewing the pin
4. move the pinhole back and forth
5. you will observe the pin is magnified when
viewed through the pinhole
this is the result of light undergoing diffraction at the pinhole
11
The Wave Nature of Matter
• Louis de Broglie theorized
all matter should exhibit
wave properties.
• He demonstrated that the
relationship between mass
and wavelength was
h
λ = mv
Louis de Broglie
λ is the de Broglie wavelength
any moving object has this
wavelength
applies to electrons, protons, atoms, bowling balls, people, etc.
electron has
wave properties
• electrons undergo
diffraction
• beams of electrons travel at
different speeds
• obey Broglie’s equation
water waves
h
λ = mv
electron waves
wave-particle duality
particle view
the size of the bubble where the particle
probably is gets very large as the particle
gets larger. For Homer it is really 99.99999..%
certain that he is where the bubble is
For electrons this behavior is easily observed.
It is called electron tunneling.
Homer is here
100% certain
tunneling is the science behind the
science fiction of teleportation
wave view
0.1 % chance
Homer is here
or
here
Homer is probably here
where his wave function
Homer’s
is big ~99% certain
de Broglie wave
aka “wave function”
or
or
here here
or
here
or
here
or
here
12
standing waves
• when waves are trapped in a space they
take on wavelengths (λ) that fit into the space
1 wavelength fits in space
2 wavelengths fits in space
only these
λ values
occur
3 wavelengths fits in space
others are
forbidden
4 wavelengths fits in space
if it is a sound wave each is approximately a different note of a chord
movie on standing waves
electrons in atoms
• electron has wave properties
• forms standing waves in the volume the
atom occupies
possible standing waves for electrons in the atoms
exactly 4 wavelengths
wrap around atom
exactly 5 wavelengths
wrap around atom
not a possible standing wave
exact number of wavelengths
will not fit in space exactly
13
quantum mechanics
• Bohr model only works on hydrogen!
• Schrodinger wave equation based
upon wave properties of the electron
• correctly predicts line spectra for all
elements for which it has been solved
• gives three-dimensional picture of
electron waves
Erwin Schrodinger
• shapes of these waves called orbitals
• also predicts properties of molecules
and ions
quantum mechanics
• Schrodinger equation has three
quantum numbers, n, l, ml
• n is similar Bohr’s n but it describes
the average distance of the electron
from the nucleus.
• l describes the orbital type or shape
• ml describes the direction the orbital
points
Erwin Schrodinger
n = 1, 2, 3 … infinity
l = 0, 1, 2 … n-1
ml = -l… 0 …. +l
these relationships taken together
describe what the sets of orbitals exist
s orbitals (l=0)
n=1
n=2
• come in sets of 1
• spherical in shape.
• size increases with increasing
value of n
• center of sphere is at nucleus
n=3
14
P orbitals
en electron has 50%
chance of being here
• sets of three orbitals
• all 3 orbitals same figure 8 shape
• oriented perpendicular to each other
• each centered at the nucleus
50% chance
of being here
d orbitals
• sets of five orbitals
• 4 orbitals have double figure 8 shape
• 1 orbital is figure 8 shape with a donut belt
• all centered at the nucleus
Principal Quantum Number, n
• like Bohr’s model the Schrodinger equation
gives integer values that describe energy of
electron (average distance from nucleus)
• quantum number n, describes the energy level
of the orbital
• The values of n are integers 1, 2, 3 …
orbital notation
n quantum
number = 2
2p
a set of 3 figure 8
shaped orbitals
15
Energies of Orbitals
set of five d orbitals
set of three p orbitals
• orbitals each have
different energies like
Bohr’s orbits
• often shown in
diagrams
• lower energy is lower
in diagram
• each orbital is a single
box
16
17