Transcript Ch. 4-2 PowerPoint

Arrangement of Electrons in
Atoms
4-2 The Quantum Model of the Atom
Electrons as Waves
Last section we learned that light can
behave as both a particle and a wave.
What about electrons?
 Louis De Broglie stated that electrons
could be considered waves confined to
a space around an atomic nucleus.
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Electron waves can exist, but only at
specific frequencies corresponding to
specific frequencies.
Electrons as Waves
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Experiments showed that electrons (like light)
could be bent, or diffracted. Also, electron beams
could interfere with each other.
 Diffraction – bending of light when passed
through a crystal.
 Interference – overlapping of waves, reducing
energy in some areas.
Heisenberg Uncertainty
Principle
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The position and momentum of a
moving object can not simultaneously
be measured and known exactly.
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Due to the duel nature of matter and
energy
Only important with small scale objects
Heisenbery Uncertainty
Principle Animation
Chapter 4 Section 2 The Quantum
Model pages 104-110
5
The Schrödinger Wave Equation
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Erwin Schrödinger developed an
equation, which treated electrons in
atoms as waves.
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Solutions to wave equation are known as
wave functions.
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Don’t worry about wave functions, we do a little more
with it in AP
Coupled with Heisenberg Uncertainty
Theory, lead to Quantum Theory
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Quantum Theory – describes
mathematically the wave properties of
The Schrödinger Wave Equation
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Most Important Idea: We can only
know the probability of finding an
electron, not its exact location.
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Orbital – a 3-dimensional region around
the nucleus that indicates the probable
location of an electron.
Fig 4-11
Review
Energy is quantized ( found in specific
amounts)
 Electrons have wavelike behavior
 Impossible to know electron position
and momentum.
 Can predict the probability of electron
location
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Called the Quantum-mechanical model
Probability and Orbital
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The density of an electron cloud is
called the electron density.
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Higher density – more likely to find
electron
Lower density – less likely to find electron
An orbital is the region where a given
electron is likely found.
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There are different types of orbitals….s,
p, d, f which we will talk about more
later.
Orbitals and Energy
 To describe orbitals, scientists use
quantum numbers.
 Quantum Number – specify the
properties of atomic orbitals and the
properties of electrons in orbitals.
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Principal Quantum Number
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indicates the main energy level occupied by the
electron.
Sometimes considered the shell.
n are positive integers (n = 1, n=2, n=3, …)
As n increases, energy and distance from nucleus
increases.
n = 1 is the lowest energy level, closest to the
nucleus.
More than one electron can have the same value
of n.
The total number of orbitals that exist in a given
shell is equal to n2.
Angular Momentum Quantum
Number (l)
indicates the shape of an orbital
 Also considered the sublevel.
 The number of orbital shapes possible
is equal to n
 l can have values of 0 and all positive
integers less than or equal to n-1
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If n = 1, l = 0: (l = n – 1 = 1 –1 = 0)
If n = 2, l = 1 and 0: (l = n – 1 = 2 – 1 = 1)
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Each orbital is assigned a letter, which
corresponds to a shape
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s orbital – see figure 4-25 pg 144
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p orbital- see figure 4-26 in book
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d orbital – see figure 4-27 in book
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Each atomic orbital is designated by the
principal quantum number followed by
the letter of the sublevel.
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Ex. 1s sublevel is the s orbital is in the
first main energy level
Ex. 2p sublevel is the set of p orbitals in
the second energy level
Ex. 3d sublevel is the set of d orbitals in
the third energy level
Magnetic Quantum Number
(ml )
indicates the orientation of an orbital around
the nucleus
 ml = +/- l and every integer in between
 Ex. If n = 1, l = 0, ml = 0
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This means there is a single s orbital in the first
energy level
If n = 2, l = 1, ml = -1, 0, +1
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In the second energy level there are three p
orbitals
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If n = 4, l = 2, ml = -2, -1, 0, +1, +2
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In the fourth energy level there are five d
orbitals.
If n = 4, l = 0, ml = 0
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In the fourth energy level there is 1 s
orbital
Spin Quantum Number (ms)
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o
indicates the spin states of an electron in an
orbital, either +1/2, or –1/2.
Electrons spin on an internal axis either clockwise
or counterclockwise.
A single orbital can hold a maximum of two
electrons, which must have opposite spins.
Summary of Energy Levels,
Sublevels, and Orbitals
Principal
Sublevels
Energy Level
n=1
1s
Orbitals
n=2
2s, 2p
2s (one) + 2p
(three)
n=3
3s, 3p, 3d
3s(one) +
3p(three)+3d(five
)
1s (one)
Max Number of Electrons in
Each Sublevel
Sublevel
# of Orbitals
s
1
Max # of
Electrons
2
p
3
6
d
5
10
f
7
14