Transcript Chapter 4.2 Quantum Models

Electrons in Atoms
The Quantum Model of the Atom
Quantum Model of Atoms
Tuesday, September 11
Take out your Chapter 4 Vocabulary Terms and Periodic
Table
Take out one sheet of paper, title “ Quantum Model of
Atoms”
1.
What changes the amount of electrons ejected in the
photoelectric effect?
2.
What is a quantum?
Quantum Model of Atoms
Wednesday, September 12
Take out your “ Quantum Model of Atoms” notes from
yesterday
Copy and Answer:
1. What does n = 3 indicate?
2.
What does l= 1 tell you about the atom?
3.
What does the angular quantum number tell you?
Photoelectric Effect Demo
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http://phet.colorado.edu/en/simulation/photoelectric
The Quantum Model of the Atom
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Electrons as Waves

French scientist Louis de Broglie suggested that electrons
should be considered waves confined to the space around
an atomic nucleus
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It followed that the electron waves could exist only at
specific frequencies (energies)

According to the relationship E = hν (Planks Law), these
frequencies corresponded to specific energies—the
quantized energies of Bohr’s orbits
The Quantum Model of the Atom
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Electrons as Waves

Electrons, like light waves, can be bent, or diffracted
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Diffraction refers to the bending of a wave as it passes by
the edge of an object or through a small opening
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Electron beams, like waves, can interfere with each other
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Interference occurs when waves overlap
Quick Lab

Does light show the wave property of
interference when a beam of light is projected
through a pinhole onto a screen?
Wave Interference
The Quantum Model of the Atom
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The Heisenberg Uncertainty Principle
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German physicist Werner Heisenberg proposed that any
attempt to locate a specific electron with a photon knocks
the electron off its course
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The Heisenberg uncertainty principle states that it is
impossible to determine simultaneously both the position
and velocity of an electron or any other particle
The Quantum Model of the Atom
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The Schrödinger Wave Equation
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In 1926, Austrian physicist Erwin Schrödinger developed
an equation that treated electrons in atoms as waves

laid the foundation for modern quantum theory
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Quantum theory describes mathematically the wave
properties of electrons and other very small particles
The Quantum Model of the Atom
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The Schrödinger Wave Equation
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Electrons do not travel around the nucleus in neat orbits, as
Bohr had postulated
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Instead, they exist in certain regions called orbitals

An orbital is a three-dimensional region around the
nucleus that indicates the probable location of an electron
The Quantum Model of the Atom

Electron Cloud
file:///D:/student/ch04/sec02/vc03/hc604_02_v03fs.htm
file:///D:/student/ch04/sec02/vc01/hc604_0
2_v01fs.htm
The Quantum Model of the Atom
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Atomic Orbitals and Quantum Numbers
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Quantum numbers specify the properties of atomic orbitals
and the properties of electrons in orbitals
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4 quantum numbers
Principal Quantum Number (1st)
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The principal quantum number, symbolized by
n
, indicates
the main energy level occupied by the electron
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Values of n are positive integers – 1, 2, 3, 4, and so on

An n increases, the electron’s energy and distance from nucleus
increases
Principal Quantum Number
e- is further from the nucleus
n=1
n=2
n=3
n=4
n=5
n=6
n=7
Angular Momentum Quantum Number (2nd)

l
The angular momentum quantum number, symbolized by ,
indicates the shape of the orbital
Value of 0, 1, 2, 3 and Represented by four sublevels ( s, p, d, f )
More about the 2nd Quantum #
l
0
1
2
3
lettershape
s
p
d
f
sphere
dumbell
dumbells +
dumbells ++
s
p
n=1
n=2
n=3
n=4
n=5
n=6
n=7
d
f
Magnetic Quantum Number (3rd)

The magnetic quantum number, symbolized by
m,
indicates the orientation of an orbital around the nucleus
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Values -l to +l
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S = spherical and centered around nucleus
P = dumbbell extended along x, y, z axis
D = cloverleaf
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
1s orbital
S
spherical
2s and 3s
1p orbital
P dumbbell shape
3p, 4p, 5p etc.
2p orbitals
similar shapes
3
larger
3 d orbitals
D cloverleaf
5
Spin Quantum Number (4th)
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The spin quantum number has only two possible values - (+1/2
, −1/2) - which indicate the spin of an electron in an orbital
Spin Continued
Within a particular orbital, there can be two electrons (take
the 2s orbital for example)
The electrons have 3 of same quantum numbers in the 2s
orbital, but cannot have all four (Pauli)
Therefore both electrons in this orbital must have different
spins (= +1/2 or -1/2)
The Quantum Model of the Atom
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Atomic Orbitals and Quantum Numbers
The Quantum Model of the Atom
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Shapes of s, p, and d Orbitals
F orbital (rarely seen at ground state)
The Quantum Model of the Atom
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Electrons Accommodated in Energy Levels and Sublevels
The Development of a New Atomic Model
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Electrons Accommodated in Energy Levels and Sublevels
The Development of a New Atomic Model
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Quantum Numbers of the First 30 Atomic Orbitals
Relationships between Quantum Numbers
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http://wps.prenhall.com/wps/media/objects/4974/5093961
/emedia/ch07/aabxgdc0.html
Review

1. What are the shapes of s, p, and d orbitals respectively?
s= spherical p = dumbbell d = cloverleaf
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2. How many 1s orbitals are there in an atom? 4p orbitals?
4d orbitals?
1s: 1 4p: 3 4d: 5
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4. Which orbitals cannot exist?
2p 3p 4d 3f 6s 2d
3f and 2d
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

How many electrons can an energy level of n = 4 hold?
(a)
32
(c)
8
(b)
24
(d)
6
Practice
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1.
2.
3.
4.
5.
6.
On the back of your Periodic Table, write the electron
configuration for the following elements:
Helium
Berilium
Nitrogen
Carbon
Arsenic
Iodine