Upload
ferdinand-wilson
View
226
Download
5
Tags:
Embed Size (px)
Citation preview
1
Chapter 11Electrons in Atoms
Killarney School
2
Section 11.1Models of the Atom
OBJECTIVES: Summarize the development of
atomic theory.
3
Section 11.1Models of the Atom
OBJECTIVES: Explain the significance of
quantized energies of electrons as they relate to the quantum mechanical model of the atom.
4
Greek Idea Democritus and
Leucippus Matter is made up
of solid indivisible particles
John Dalton - one type of atom for each element
5
J. J. Thomson’s Model
Discovered electrons Atoms were made of
positive stuff Negative electron
floating around “Plum-Pudding”
model
6
Ernest Rutherford’s Model Discovered dense
positive piece at the center of the atom- nucleus
Electrons would surround it
Mostly empty space
“Nuclear model”
7
Niels Bohr’s Model He had a question: Why don’t the
electrons fall into the nucleus? Move like planets around the sun. In circular orbits at different levels. Amounts of energy separate one
level from another. “Planetary model”
8
Bohr’s planetary model Energy level of an electron analogous to the rungs of a ladder electron cannot exist between energy
levels, just like you can’t stand between rungs on ladder
Quantum of energy required to move to the next highest level
9
The Quantum Mechanical Model
Energy is quantized. It comes in chunks. A quanta is the amount of energy needed to
move from one energy level to another. Since the energy of an atom is never “in
between” there must be a quantum leap in energy.
Erwin Schrodinger derived an equation that described the energy and position of the electrons in an atom
10
Things that are very small behave differently from things big enough to see.
The quantum mechanical model is a mathematical solution
It is not like anything you can see.
The Quantum Mechanical Model
11
Has energy levels for electrons.
Orbits are not circular. It can only tell us the
probability of finding an electron a certain distance from the nucleus.
The Quantum Mechanical Model
12
The atom is found inside a blurry “electron cloud”
A area where there is a chance of finding an electron.
Draw a line at 90 % Think of fan blades
The Quantum Mechanical Model
13
Atomic Orbitals Principal Quantum Number (n) = the
energy level of the electron.(1-7) Sublevels- like theater seats arranged
in sections(labeled s,p,d,f) Within each sublevel, the complex math
of Schrodinger’s equation describes several shapes.
These are called atomic orbitals - regions where there is a high probability of finding an electron.
14
For any atom there is only one 1s orbital. The "1" represents the fact that the orbital is in theenergy level closest to thenucleus. The "s" refers to the shape of the orbital. S orbitals are spherically symmetric around the nucleus.
15
1 s orbital
2 s and 3 s orbitals just larger
16
2p and 3p orbitalsAt the first energy level, the only orbital available to electrons is the 1s orbital, but at the second and third levels, as well as the 2s and 3s orbitals, there are also the 2p and 3p orbitals.Unlike an s orbital a p orbital points in a particular direction. At any one energy level it is possible to have three absolutely equivalent p orbitals pointing mutually at right angles to each other. These are arbitrarily given the symbols px, py and pz
17
2 px orbital “dumb bell shape”
18
19
20
3 d orbital
21
Videos of Atomic Orbitals
http://www.humboldt.edu/~chem_dpt/resources/C109_AOSup_1-6.htm
22
s2 Principle energy level 1
Principle energy level 2
Principle energy level 3
Principle energy level 4
Principle energy level 5
Principle energy level 6
Principle energy level 7
s2 p6
s2 p6
s2 p6 d10
s2 p6 d10
s2 p6 d10
f14
s2
f14
Increasing energy
p6
d10
23
24
s
p
d
f
# of shapes
Max electrons
Starts at energy level
1 2 1
3 6 2
5 10 3
7 14 4
25
Orbital Shapes S - spherical P - dumb bell
26
By Energy Level First Energy Level only s sublevel only 2 electrons 1s2
Second Energy Level
s and p sublevels are available
2 e- in s, 6 in p 2s22p6
8 total electrons
27
By Energy Level Third energy level s, p, and d
sublevels 2 e- in s, 6 in p,
and 10 in d 3s23p63d10
18 total electrons
Fourth energy level s,p,d, and f
sublevels 2 e- in s, 6 in p, 10
in d, and 14 in f 4s24p64d104f14
32 total electrons
28
By Energy Level Any more than
the fourth and not all the orbitals will fill up.
You simply run out of electrons
The orbitals do not fill up in a neat order.
The energy levels overlap
Lowest energy fill first.
29
Section 11.2Electron Arrangement in Atoms
OBJECTIVES: Apply the aufbau principle, the
Pauli exclusion principle, and Hund’s rule in writing the electron configurations of elements.
30
Section 11.2Electron Arrangement in Atoms
OBJECTIVES: Explain why the electron
configurations for some elements differ from those assigned using the aufbau principle.
31
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
Aufbau diagram - page 251
32
Electron Configurations The way electrons are arranged in
atoms. Aufbau principle- electrons enter the
lowest energy first. This causes difficulties because of the
overlap of orbitals of different energies. Pauli Exclusion Principle- at most 2
electrons per orbital - different spins
33
Electron Configuration Hund’s Rule- When electrons
occupy orbitals of equal energy they don’t pair up until they have to.
Let’s determine the electron configuration for Phosphorus
Need to account for 15 electrons
34
The first two electrons go into the 1s orbital
Notice the opposite spins
only 13 more to go...
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
35
The next electrons go into the 2s orbital
only 11 more...Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
36
• The next electrons go into the 2p orbital
• only 5 more...Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
37
• The next electrons go into the 3s orbital
• only 3 more...Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
38
Incr
easi
ng e
nerg
y
1s
2s
3s
4s
5s6s
7s
2p
3p
4p
5p
6p
3d
4d
5d
7p 6d
4f
5f
• The last three electrons go into the 3p orbitals.
• They each go into separate shapes
• 3 unpaired electrons
• = 1s22s22p63s23p3
39
The easy way to remember
1s2s 2p3s 3p 3d4s 4p 4d 4f
5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f
• 1s2
• 2 electrons
40
Fill from the bottom up following the arrows
1s2s 2p3s 3p 3d4s 4p 4d 4f
5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f
• 1s2 2s2
• 4 electrons
41
Fill from the bottom up following the arrows
1s2s 2p3s 3p 3d4s 4p 4d 4f
5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f
• 1s2 2s2 2p6 3s2
• 12 electrons
42
Fill from the bottom up following the arrows
1s2s 2p3s 3p 3d4s 4p 4d 4f
5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f
• 1s2 2s2 2p6 3s2
3p6 4s2
• 20 electrons
43
Fill from the bottom up following the arrows
1s2s 2p3s 3p 3d4s 4p 4d 4f
5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f
• 1s2 2s2 2p6 3s2
3p6 4s2 3d10 4p6
5s2
• 38 electrons
44
Fill from the bottom up following the arrows
1s2s 2p3s 3p 3d4s 4p 4d 4f
5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f
• 1s2 2s2 2p6 3s2
3p6 4s2 3d10 4p6
5s2 4d10 5p6 6s2
• 56 electrons
45
Fill from the bottom up following the arrows
1s2s 2p3s 3p 3d4s 4p 4d 4f
5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f
• 1s2 2s2 2p6 3s2
3p6 4s2 3d10 4p6
5s2 4d10 5p6 6s2
4f14 5d10 6p6 7s2
• 88 electrons
46
Fill from the bottom up following the arrows
1s2s 2p3s 3p 3d4s 4p 4d 4f
5s 5p 5d 5f6s 6p 6d 6f7s 7p 7d 7f
• 1s2 2s2 2p6 3s2
3p6 4s2 3d10 4p6
5s2 4d10 5p6 6s2
4f14 5d10 6p6 7s2
5f14 6d10 7p6 • 108 electrons
47
Exceptional Electron Configurations
48
Orbitals fill in order Lowest energy to higher energy. Adding electrons can change the
energy of the orbital. Half filled orbitals have a lower
energy. Makes them more stable. Changes the filling order
49
Write these electron configurations
Titanium - 22 electrons 1s22s22p63s23p64s23d2
Vanadium - 23 electrons 1s22s22p63s23p64s23d3
Chromium - 24 electrons 1s22s22p63s23p64s23d4 expected But this is wrong!!
50
Chromium is actually: 1s22s22p63s23p64s13d5
Why? This gives us two half filled orbitals. Slightly lower in energy. The same principal applies to
copper.
51
Copper’s electron configuration
Copper has 29 electrons so we expect: 1s22s22p63s23p64s23d9
But the actual configuration is: 1s22s22p63s23p64s13d10
This gives one filled orbital and one half filled orbital.
Remember these exceptions: d4, d9
52
Section 11.3Physics and the Quantum
Mechanical Model OBJECTIVES:
Calculate the wavelength, frequency, or energy of light, given two of these values.
53
Section 11.3Physics and the Quantum
Mechanical Model OBJECTIVES:
Explain the origin of the atomic emission spectrum of an element.
54
Light The study of light led to the
development of the quantum mechanical model.
Light is a kind of electromagnetic radiation.
Electromagnetic radiation includes many kinds of waves
All move at 3.00 x 108 m/s = c
55
Parts of a wave
Wavelength
AmplitudeOrigin
Crest
Trough
56
Parts of Wave - p.255 Origin - the base line of the energy. Crest - high point on a wave Trough - Low point on a wave Amplitude - distance from origin to crest Wavelength - distance from crest to
crest Wavelength is abbreviated by the Greek
letter lambda =
57
Frequency The number of waves that pass a
given point per second. Units: cycles/sec or hertz (hz or sec-1) Abbreviated by Greek letter nu =
c =
58
Frequency and wavelength Are inversely related As one goes up the other goes down. Different frequencies of light are
different colors of light. There is a wide variety of frequencies The whole range is called a spectrum,
Fig. 11.15, page 256
59
Radiowaves
Microwaves
Infrared .
Ultra-violet
X-Rays
GammaRays
Low energy
High energy
Low Frequency
High Frequency
Long Wavelength
Short WavelengthVisible Light
60
Prism White light is
made up of all the colors of the visible spectrum.
Passing it through a prism separates it.
61
If the light is not white By heating a gas
with electricity we can get it to give off colors.
Passing this light through a prism does something different.
62
Atomic Spectrum Each element
gives off its own characteristic colors.
Can be used to identify the atom.
How we know what stars are made of.
63
• These are called discontinuous spectra, or line spectra
• unique to each element.
• These are emission spectra
• The light is emitted (given off)
• Sample 11-16/17 p.257/58
64
Light is a Particle Energy is quantized. Light is energy Light must be quantized These smallest pieces of light are
called photons. Photoelectric effect? Energy & frequency: directly related.
65
Energy and frequency E = h x E is the energy of the photon is the frequency h is Planck’s constant h = 6.6262 x 10 -34 Joules x sec. joule is the metric unit of Energy
66
The Math in Chapter 11
2 equations so far:
c = E = h Know these!
67
Examples What is the wavelength of blue light
with a frequency of 8.3 x 1015 hz? What is the frequency of red light
with a wavelength of 4.2 x 10-5 m? What is the energy of a photon of
each of the above?
68
Explanation of atomic spectra When we write electron
configurations, we are writing the lowest energy.
The energy level, and where the electron starts from, is called it’s ground state- the lowest energy level.
69
Changing the energy Let’s look at a hydrogen atom
70
Changing the energy Heat or electricity or light can move the
electron up energy levels (“excited”)
71
Changing the energy As the electron falls back to ground
state, it gives the energy back as light
72
May fall down in steps Each with a different energy
Changing the energy
73
{{{
74
Further they fall, more energy, higher frequency.
This is simplified the orbitals also have different energies
inside energy levels All the electrons can move around.
Ultraviolet Visible Infrared
75
What is light? Light is a particle - it comes in chunks. Light is a wave- we can measure its
wavelength and it behaves as a wave If we combine E=mc2 , c=, E = 1/2 mv2
and E = h We can get: = h/mv called de Broglie’s equation Calculates the wavelength of a particle.
76
Sample problem What is the approximate mass of a
particle having a wavelength of 10-7 meters, and a speed of 1 m/s? Use = h/mv
= 6.6 x 10-27
(Note: 1 J = N x m; 1 N = 1 kg x m/s2
77
Matter is a Wave Does not apply to large objects Things bigger than an atom A baseball has a wavelength of
about 10-32 m when moving 30 m/s An electron at the same speed has
a wavelength of 10-3 cm Big enough to measure.
78
The physics of the very small Quantum mechanics explains how
the very small behaves. Classic physics is what you get
when you add up the effects of millions of packages.
Quantum mechanics is based on probability
79
Heisenberg Uncertainty Principle
-It is impossible to know exactly the location and velocity of a particle.
The better we know one, the less we know the other.
Measuring changes the properties. Instead, analyze interactions with
other particles
80
More obvious with the very small
To measure where a electron is, we use light.
But the light moves the electron And hitting the electron changes the
frequency of the light.
81
Moving Electron
Photon
Before
Electron Changes velocity
Photon changes wavelength
After
Fig. 11.26, p. 265