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Es 34
Electronic structure of Atoms
What is an atom?
12
orprotons
e
C
charge
Electron “cloud”
6
Too many or too few electrons?…
Nucleus
(protons and
neutrons)
When atoms come together to form chemical species:
Electron clouds will interact!
Electrons are small, but they determine the chemical properties
and the physical properties of an atom.
1
How are electrons organized within this cloud?
The electronic structure
• An orbital is a wave function that describes where an electron can be found around the nucleus (3D space)
and how much energy it has.
• There are several kinds of orbitals, each with a characteristic shape, size and energy.
• Each orbital can contain a maximum of 2 electrons.
✓ Recognize atomic orbital shapes (s, p and d) and predict their relative energies.
2
1
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How are electrons organized within this cloud?
The electronic structure
• An orbital is a wave function that describes where an electron can be found around the nucleus (3D space)
and how much energy it has.
• There are several kinds of orbitals, each with a characteristic shape, size and energy.
• Each orbital can contain a maximum of 2 electrons.
• Subshells are collections of orbitals with a similar shape.
• Each subshell is described by a letter (s, p, d, f, …).
• All orbitals in the same subshell have a similar shape but a different orientation in space.
✓ Recognize atomic orbital shapes (s, p and d) and predict their relative energies.
3
How are electrons organized within this cloud?
The electronic structure
• An orbital is a wave function that describes where an electron can be found around the nucleus (3D space)
and how much energy it has.
• There are several kinds of orbitals, each with a characteristic shape, size and energy.
• Each orbital can contain a maximum of 2 electrons.
• Subshells are collections of orbitals with a similar shape.
• Each subshell is described by a letter (s, p, d, f, …).
• All orbitals in the same subshell have a similar shape but a different orientation in space.
size
n=2
Energy
• Shells describe subshells with a similar size and energy.
• Shells also known as energy levels, and are numbered (n = 1, 2, 3, …).
• Lower-numbered shells are lower energy and smaller.
inciters
✓ Recognize atomic orbital shapes (s, p and d) and predict their relative energies.
7
n=1
4
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More details about these
orbitals…
What do we need to know?
5
s orbitals
2s
1s
Shell #
do
Subshell letter
s orbitals are spherical.
There is only one s orbital per subshell (only one orientation possible).
The s subshell is the lowest-energy subshell in any energy level.
✓ Recognize atomic orbital shapes (s, p and d) and predict their relative energies.
6
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p orbitals
Node
Tony
or
Each p orbitals is made of two lobes separated by a node.
– a region where there is zero electron density.
There are three possible orientations for p orbitals (x, y, z) – and so three p orbitals per
subshell.
The p subshell is higher energy than the s subshell in the same energy level.
0
I
o
7
✓ Recognize atomic orbital shapes (s, p and d) and predict their relative energies.
7
Energy level diagram
The combined effect of nuclear attraction, electron repulsion, and orbital shape lead to the splitting
of the shells into subshell-based energy levels:
n
*within a shell: Es < Ep < Ed
p p g
n2
r
ni
n
degenerate
s
Note: All orbitals in one subshell are
degenerate, meaning they have the
same energy.
✓ Recognize atomic orbital shapes (s, p and d) and predict their relative energies.
8
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4lobesjust
d orbitals
of 2
instead
d orbitals have two planar nodes.
There are five possible orientations and so five d orbitals per subshell.
The d subshell is higher energy than the s and p subshells in the same
energy level.
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g
y
x
y
x
✓ Recognize atomic orbital shapes (s, p and d) and predict their relative energies.
y
z
9
9
Why do we need to know about
orbitals?
Electronic configuration
need
tousethemifwewanttodefine
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ourelectronicstructureand
10
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Electron configurations
12
6
Expressing the organization of electrons into their various shells / subshells / orbitals
is the electron configuration for an atom.
MOSTSTABLE
To build a ground state electron configuration, we follow 3 rules:
1. Electrons must occupy the lowest energy level available.
2. Within a partially filled subshell, electrons should be divided amongst the
different orbitals.
3. If electrons must occupy the same orbital, they should be spin paired.
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Different notations:
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Example
ooxsiag.am
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c
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or C15252ps
6 protons
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O
Which orbital(s)?
pray th
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electrons
C
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✓ Write electron configurations (full and condensed) and orbital diagrams for s & p-block elements with Z ≤ 54.
11
Core and Valence electrons
• Valence electrons are the highest energy electrons of an atom, found in the outermost shell (i.e. the
electrons with the highest value of n).
• These are the electrons that are usually involved in reactivity and bonding for an atom.
• Electrons in the inner shells are core electrons.
Practice: How many valence electrons are in carbon? has4valanceelectrons
na
toreact
Shorthand notation: Use the next-smallest noble gas as a shorthand
for the core electrons of an atom.
C 15252,2
w
carton iwe
represent
before
comes
that
c
an
just
C t
a sanelinmatom
electrons
the
core
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Energy
for
shell carbon
highest
Energy
Valanceelectrons
Thesearetheonesmostlikley
e lectrons
core
cinemoststane
lowest
amountenergy
and
of
✓ Write electron configurations (full and condensed) and orbital diagrams for s & p-block elements with Z ≤ 54.
12
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Electron configurations
What would be an excited state e- configuration?
One (or more) electrons is occupying an energy level that is higher than it should.
15252 ground
Cexcited
is2s2ps
atatz.ae
incomplete.no
15252ps and
exponents
Energy
Cexcited
y
IMPORTANT: The total number of
electrons should remain the same.
itztatEa VALANCEELECTRONS C
✓ Write electron configurations (full and condensed) and orbital diagrams for s & p-block elements with Z ≤ 54.
13
Electron configurations of ions
Which electron would be lost first?
the
The highest energy electron is the least stable one. This is the first one to be lost.
15252ps
se
Follow the same rules.
Add the electron to the lowest energy
orbital that is available.
Energy
Where would you add an extra electron?
C 152,52ps Te
✓ Write electron configurations (full and condensed) and orbital diagrams for s & p-block elements with Z ≤ 54.
14
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Practice Problem (ES 33 & 34)
a.
What is the electron configuration of an
atom of phosphorus in its ground state?
gassustomore
Pine
c c say
PNe3s3p
b.
What would be the electron configuration
for a P+ ion?
c.
What would be the electron configuration
for a P– ion?
P Ne3s3p
Draw 5 different The
orbitals for a phosphorus
atom. Note: your orbitals should belong to
different subshells and the relative size
should be considered when drawing.
d.
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I.se
PEY3 É
a.m
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s
25
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as zigsp
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15
Summary Slides
16
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Summary Slides
17
9
Es 35
Atomic properties
Trends in physical properties & reactivity
atomic size, ionization energy, electron affinity
e-
• Trends can be rationalized by relating them to:
?
+
• How far are the valence electrons from the nucleus?
• n value
• size of orbitals
Electrostatic attractions?
• What is the nuclear charge (pull) felt by the valence electrons?
• Effective nuclear charge (Zeff)
Electron configuration
Orbital size & energy
✓ Relate electron configurations to periodic trends in atomic/ionic radius, ionization energy, and electron affinity.
1
Effective nuclear charge, Zeff
• Electrons in the core shells shield the valence electrons from some of the nuclear
charge.
• The valence electrons feel less of the electrostatic attraction to the nucleus than
core electrons.
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lithium
Example
with
is's
ww
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z.azC
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nucleus
• We can approximate as:
Zeff = Z – (# e-core)
3
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Lower
nuclear
stronger
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s
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electron
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and
and
where z full
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electrons
core
enamor
✓ Relate electron configurations to periodic trends in atomic/ionic radius, ionization energy, and electron affinity.
2
1
Trends in atomic size
sire
Ma
✓ Relate electron configurations to periodic trends in atomic/ionic radius.
3
Trends in Ionization Energies
First ionization
• The first ionization energy describes the energy required to remove one electron from
the neutral atom.
X (g) ⟶ X+ (g) + e−
IE1
• This is an endothermic process – we must put energy in to ionize the atom.
✓ Relate electron configurations to periodic trends in ionization energy.
4
2
Trends in Ionization Energies
First ionization
Zeff
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as
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2
g
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seen
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n
5
Trends in Ionization Energies
successive ionization
• As more electrons are removed from an atom, further ionization becomes more
difficult.
• Removing electrons from an atom’s core shells is MUCH more difficult than
removing valence electrons.
cost
Energy
X (g) ⟶ X+ (g) + e−
IE1
X+ (g) ⟶ X2+ (g) + e− IE2
IELIERIE
IEualanceCIEcore
X2+ (g) ⟶ X3+(g) + e− IE3
6
3
Trends in Electron Affinities
• Electron affinity is the energy associated with the addition of an electron to an atom
(or ion).
X + e − ⟶ X−
EA1
AH 0
enthalpy
• Most electron affinities are negative (exothermic). The more heat is released, the
higher the affinity is for the incoming electron.
Zeff
Higher
Affinity
Higher
Affinity
n
Lower
affinity
voffinity
7
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