Transcript Chapter 4 Electron Configurations

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?
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?
Electromagnetic Spectrum
Types of waves: Infrared
Types of waves: x-rays
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?


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?


Up the ramp/stairs
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 eto 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?


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?


The nrg emitted/absorbed by any object is restricted to fixed amounts
called quanta
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=_5F
34NFWVL4
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
Photo courtesy NASA
Hydrogen spectrum
Photo courtesy NASA
Helium spectrum
Why does it take
more nrg for the
painter to climb to
the top rung of the
ladder?
The painter is
moving farther away
from Earth’s surface
climbing to the top
rung.
The electrons of an
atom occupy orbitals
around the atom’s
nucleus that are
similar to the rungs of
a ladder.
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?
The paintbrush
had more potential
energy at the top
of the ladder.
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 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
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
4-3 Section Review
What is the difference b/w a line spectrum and a continuous
spectrum?
1.
1.
How does the Bohr model account for the line spectrum of the
hydrogen atom?
2.
1.
The Bohr model labels the different nrg levels wh. Can be occupied by an e-. The eabsorbs/emits a certain quantity of nrg when it moves b/w these nrg levels. The
frequencies in the line spectrum of hydrogen correspond to the quantity of nrg
emitted when an e- moves from a higher to lower state.
What is Heisenberg’s Uncertainty Principle?
3.
1.
4.
Line spectrum contains only certain colors/wavelengths. Continuous spectrum
contains all colors, wh. Fade gradually into ea. other
States the position and momentum of a moving object can’t simultaneously be
measured and known exactly
You have learned that in attempting to locate an e-. The act of
measurement changes the system. Suppose that you measure the temp.
of a cup of hot tea with a cold thermometer. How does the use of the cold
thermometer affect the temp reading? Is this an example of the
uncertainty principle? Explain.
4-4 A New Approach to the
Atom
WHAT IS AN ATOMIC ORBITAL? HOW DO THE
S, P, D, AND F ORBITALS COMPARE IN SIZE,
SHAPE, AND ENERGY?
Quantum Mechanical Model
 Model of the atom
 Explains properties of the atom by treating electrons
as waves that have quantized their energies
 Though unable to tell exactly where an electron is or
how it is moving

Model does describe probability that electrons will be found in
certain locations around the nucleus
Probability and Orbitals
 Electrons are seen in a blurry cloud or negative
charge – electron cloud
 More dense the area, the more probable to find
electrons
 Electron density: density of an electron cloud


High probability – high electron density
Low probability – low electron density
Probability and Orbitals
 The probability of finding electrons in certain
regions of an atom is described by orbitals
 An atomic orbital is a region around the nucleus of
an atom where an electron with a given energy is
likely to be found
 Orbitals have characteristic shapes, sizes, and
energies
Probability and Orbitals
 4 kinds of orbitals
 s, p, d, and f

s orbital



p orbital


Dumbbell/figure eight
shaped
d orbital


Circle shaped
Increase in size w/ ea.
increase in nrg level
No definite shape
f orbital

No definite shape
Orbitals and Energy
 Bohr suggested energies in electrons were quantized
 These quantizations labeled as principle quantum levels
designated by quantum #, n
 Quantum Mechanical Model adds sublevels to these
principle quantum levels


Sublevels have a pattern
# of sublevels equals the quantum #
n = 1 – 1 sublevel
 n = 2 – 2 sublevels, etc

Orbitals and Energy
Orbitals and Energy
 Just like an address
 You have a name, street, city, state, and zipcode
 An electron has its principal energy level, the
sublevel, and its orbital within that sublevel
 First energy level


n=1
One sublevel – s

Called the 1s sublevel and 1s orbital
Orbitals and Energy
 Second energy level
 n=2
 2 sublevels
2s – slightly larger than 1s
 2p – consists of 3 orbitals


(px, py, pz)
• x, y, & z stand for axis (3D)
Orbitals and Energy
 3rd principle energy level


n=3
3 sublevels
3s
 3p
 3d – five orbitals

Orbitals and Energy
 4th principal energy level


n=4
4 sublevels
4s
 4p
 4d
 4f – 7 orbitals

Electron Spin
 Electrons spin either clockwise or counterclockwise
 Each orbit has 2 electrons
 Each electron will have an opposite spin

Represented as arrows
4-4 Review (p 146 1-4)
 What is an atomic orbital? An electron orbit?
 Sketch the general shape of an s orbital and of a p
orbital.
 List the kinds of sublevels in the fourth principal
energy level of an atom.
 How many electron can be found in any orbital of an
atom? Are their spins parallel or opposite?
Ground-State e- Configuration
 Atoms want all their e- in a pattern and where they
are supposed to be (organized)
 When an atom has a lot of e-, they want them in the
lowest nrg levels as possible
Aufbau Principle
 All sublevels of an nrg level have equal nrg
 For example, in the 2p sublevel, the 2px, 2py, and 2pz orbitals
are all equal in size
 An f sublevel has more nrg than a d orbital, wh. has
more nrg than a p, wh. has more nrg than an s

For example, a 2p is larger than a 2s
Aufbau Cont
 It is possible for sublevels in one nrg level to overlap
sublevels in another nrg level

For example, looking at nrg, a 4s orbital would be smaller than
a 3d orbital

We would normally think they would go in order
Pauli Exclusion Principle
 There are two e- in ea. orbital
 ea. one has a different spin to it.
 A 2s orbital would have 2 e- in it
 A 2p orbital would have 2 e- in ea. of its orbitals (x, y, and z)
 These different spins, mean one is spinning
clockwise and the other counterclockwise.
Hund’s Rule
 For ea. orbital in a sublevel (s, p, d, or f) will need
special placement of the e There are 2 e- in ea. orbital, for however many
orbital you have w/in a sublevel (1 for s, 3 for p, etc),
you will need to place e- with the same spin in first
and then add the others
 Let’s look at some examples
Hund’s Rule
1.
4.
2.
5.
3.
6.
Orbital Diagrams
 A way to represent the e- in an atom
 Lets you see the different spins in an orbital
 What does it look like?
 Empty box – empty orbital
 Single up arrow – orbital w/ 1 e Up and down arrow – orbital w/ 2 e-
Orbital Diagrams Cont.
 Let’s look at Carbon
 When we look at the periodic table, Carbon has an atomic #
of 6
 we know that means there are also 6 e Let’s put them in our boxes, but put them in order of orbitals
1s
2s
2p
Orbital Diagrams
 With a partner, draw the orbital diagrams for
Helium, Oxygen, and Fluorine
Electron Configuration Notation
 Another way to represent the e- in an atom
 Instead of drawing boxes, you make a list
 For our Carbon example, we had 6 e- total
 1s22s22p2
 We have a chart we can use to let us know which orbitals to
place in our list first
e- configurations
 With your partner, write the e- configurations of
Helium, Oxygen, and Fluorine.