Chapter 8:
Electron Configurations and the
Periodic Table
Chem 6A, Section D Oct 25, 2011
Chem 6A Michael J. Sailor, UC San Diego
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The Periodic Table of the Elements
Chem 6A Michael J. Sailor, UC San Diego
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Electron Configurations
Aufbau ="Building up"
As each proton is added to the nucleus, you
add an electron to the hydrogen-like
orbitals.
Add to s, then d, then p orbitals of the same
principle quantum number
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Chem 6A Michael J. Sailor, UC San Diego
Quantum numbers
Quantum
Number
Called
Describes
n
l
Principle quantum number
SIZE and ENERGY
Angular momentum
(Azimuthal) quantum number
SHAPE
ml
Magnetic quantum number
ORIENTATION
ms
Electron spin quantum
number
INTRINSIC
ANGULAR
MOMENTUM OF
THE ELECTRON
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The Periodic Table of the Elements
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Chem 6A Michael J. Sailor, UC San Diego
The Periodic Table of the Elements
1s
2s
3s
4s
5s
6s
7s
3d
4d
5d
Chem 6A Michael J. Sailor, UC San Diego
2p
3p
4p
5p
6p
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Electron Configurations
How to fill up orbitals with electrons?
• Electrons go in lowest energy orbital first,
they spread over all the empty orbitals with
the same spin, then they pair up.
• Pauli Exclusion Principle: No more than 2
electrons per orbital, must be of opposite
spin.
• Hund's rule: When there is more than one
orbital with the same energy, fill up empty
orbitals first, keeping the spins the same.
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Chem 6A Michael J. Sailor, UC San Diego
The Building-up Principle
(aufbau)
Pauli exclusion principle: no more
than 2 electrons in each orbital. Pairs of
electrons in the same orbital must have
opposite spins.
Hund’s rule: When there is more than
one orbital with the same energy
(degenerate), fill up empty orbitals with
one electron before pairing the
electrons, keep the spins the same.
from T. Moeller “Inorganic Chemistry”
Wiley 1952
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Similar figure in your textbook
Chem 6A Michael J. Sailor, UC San Diego
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Stern-Gerlach Experiment:
Ag atoms
Screen
OVEN
Containing Ag
Magnet
The atoms split into two paths in a magnetic field
This experiment tells us that each individual electron has a
magnetic moment; there must be a 4th quantum number: Electron
spin, or ms
Chem 6A Michael J. Sailor, UC San Diego
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Electron Configurations
Example Electron configurations:
Potassium 1s22s22p63s23p64s1
shorthand: [Ar]4s1
Vanadium [Ar]4s23d3
Selenium [Ar]4s23d104p4
Note: (n+1)s orbitals always fill up before nd.
4f and 5d orbitals have similar energies, Lanthanides fill up
4f and 5d orbitals in somewhat random order. Don’t worry
about lanthanides for now.
Chem 6A Michael J. Sailor, UC San Diego
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Electron Configurations
Chem 6A Michael J. Sailor, UC San Diego
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Electron Configurations-Exceptions
Exceptions: everything fills up normally, with
a few exceptions:
Cr: [Ar]4s13d5
Why? half-filled shells are unusually stable.
This one you can't predict, just memorize.
Cu: [Ar]4s13d10
Why? fully-filled shells are stable.
Memorize these
Chem 6A Michael J. Sailor, UC San Diego
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Ordering of s, p, d, and f orbitals
Relative ENERGIES:
s<p<d<f
Fill ns, then np, then nd orbital. Example (V):
Vanadium: 1s22s22p63s23p64s23d3
You always fill up (n+1)s before nd. Why?
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Chem 6A Michael J. Sailor, UC San Diego
Ordering of s, p, d, and f orbitals
You always fill up (n+1)s before nd. Why?
Main factors determining relative energy ordering for
orbitals with the same value of n:
– Nuclear charge
–
3 s orbital
Electron-electron repulsion (shielding)
3 px orbital
3 dxz orbital
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www.rsc.org/chemsoc/visualelements/orbital/
Chem 6A Michael J. Sailor, UC San Diego
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Ordering of s, p, d, and f orbitals
ORBITAL SHAPE: Which orbital allows the
electrons to get closer to the nucleus?
Radial Probability Functions
1s
Ψ2 (probabbility)
The electron
likes to get
closer to the
nucleus if it can,
so it goes into
the s orbital
before the p
orbital
2s
has greater probability
“Electron
close to the nucleus than 2p
Penetration”
2p
2s
0
1
2
3
r, Bohr radii
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Chem 6A Michael J. Sailor, UC San Diego
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6
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Electron Penetration
The lower the value of l, the greater the
penetration.
Relative ENERGIES:
s < p < d < f
Chem 6A Michael J. Sailor, UC San Diego
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Chem 6A Michael J. Sailor, UC San Diego
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Periodic Trends
ATOMIC RADII Relative size of atoms
IONIC RADII Relative size of ions
IONIZATION ENERGY
ELETRON AFFINITY
Chem 6A Michael J. Sailor, UC San Diego
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Periodic Trends:
ATOMIC RADII
Fig 8.8
TREND:
• small on top, big on
bottom
• shrink going L to R,
because nuclear charge
is increasing w/o
increasing n
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Chem 6A Michael J. Sailor, UC San Diego
Periodic Trends: ATOMIC RADII
Fig 8.9
Chem 6A Michael J. Sailor, UC San Diego
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Problem: Atomic Radius
Rank the following set of main group
elements in order of decreasing atomic size:
Br, Rb, Kr, Ca, Sr
Chem 6A Michael J. Sailor, UC San Diego
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Solution: Atomic Radius
Rank in order of decreasing atomic size: Br,
Rb, Kr, Ca, Sr
Elements with n = 4: Br, Kr, Ca
Size increases going L->R, so big to small is
Ca > Br > Kr
Elements with n = 5: Rb, Sr
Size increases going L->R, so big to small is
Rb > Sr
Chem 6A Michael J. Sailor, UC San Diego
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Solution: Atomic Radius
Rank in order of decreasing atomic size: Br,
Rb, Kr, Ca, Sr
Is Sr > Ca or is Ca > Sr?
Sr > Ca, so the final ranking is
Rb > Sr > Ca > Br > Kr
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Chem 6A Michael J. Sailor, UC San Diego
Periodic Trends: IONIC RADII
Fig 8.20
Chem 6A Michael J. Sailor, UC San Diego
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Periodic Trends: IONIC RADII
Fig 8.21
Chem 6A Michael J. Sailor, UC San Diego
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Periodic Trends: IONIZATION ENERGY
and ELECTRON AFFINITY
• IONIZATION ENERGY:
A → A+ + e-
• ELECTRON AFFINITY:
A + e - → A-
They are not the reverse of each other!
Chem 6A Michael J. Sailor, UC San Diego
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Periodic Trends: IONIZATION ENERGY
Fig 8.10
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Chem 6A Michael J. Sailor, UC San Diego
Periodic Trends: IONIZATION ENERGY
It is really hard to pull an electron from He
Fig 8.11
It is really easy to pull an electron from Cs
Chem 6A Michael J. Sailor, UC San Diego
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Periodic Trends: ELECTRON AFFINITY
Fig 8.13
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Periodic Trends: ELECTRON AFFINITY
ELECTRON AFFINITY:
Can be either exothermic or endothermic
Chem 6A Michael J. Sailor, UC San Diego
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Periodic Trends: SUMMARY
Fig 8.14
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Chem 6A Michael J. Sailor, UC San Diego
Periodic Trends: IONIZATION ENERGY
Fig 8.12
1st, 2nd, and 3rd
ionization energies
for Beryllium
(Be)
Why is 3rd IE so
much larger than
1st or 2nd IE?
Chem 6A Michael J. Sailor, UC San Diego
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Problem: Predicting Common Oxidation
States from Ionization Energy
The ionization energies for lead are given below. Based on this
information, predict the common oxidation states for this element.
Chem 6A Michael J. Sailor, UC San Diego
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Lead in the Washington, DC
water supply
March 12, 2004 Steve Curwood radio interview
with Marc Edwards on “Living on Earth:”
D.C. WATER WOES
CURWOOD: “Last year, at the request of some
Washington, D.C. residents, Marc Edwards, a civil
engineer and corrosion specialist with Virginia Tech,
began testing the quality of drinking water being piped
into their homes. Soon, he says, he found
concentrations of lead in that water that he describes as
being literally off the charts. Some of the levels were so
high that the water could be considered hazardous
waste.”
http://www.loe.org/ETS/organizations.php3?action=printContentItem&orgid=33&typeID=18&itemID=195#feature3
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Chem 6A Michael J. Sailor, UC San Diego
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Solution: Predicting Common Oxidation
States from Ionization Energy
7000
IE, KJ/mol
6000
5000
Pb3+ → Pb4+
4000
3000
2000
Pb+ → Pb2+
1000
0
1
2
3
State
4
5
Pb2+, Pb4+ are the most common
oxidation states for Pb.
Chem 6A Michael J. Sailor, UC San Diego
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Inert Pairs
Sn2+, Tl+, Pb2+, Bi3+ are stable ions, even
though they do not have a noble gas
configuration:
Pb: [Xe] 6s25d106p2
Pb2+: [Xe] 6s25d10
Pb4+: [Xe] 5d10
The s electrons are not as easily removed in these
elements--a pair of s electrons is “inert”
Common oxides of lead: PbO, PbO2
Chem 6A Michael J. Sailor, UC San Diego
36
Lead in the Washington, DC
water supply
March 12, 2004 Steve Curwood radio interview
with Marc Edwards on “Living on Earth:”
D.C. WATER WOES
CURWOOD: “Last year, at the request of some
Washington, D.C. residents, Marc Edwards, a civil
engineer and corrosion specialist with Virginia Tech,
began testing the quality of drinking water being piped
into their homes. Soon, he says, he found
concentrations of lead in that water that he describes as
being literally off the charts. Some of the levels were so
high that the water could be considered hazardous
waste.”
http://www.loe.org/ETS/organizations.php3?action=printContentItem&orgid=33&typeID=18&itemID=195#feature3
Chem 6A Michael J. Sailor, UC San Diego
37
Use of monochloramine in water
purification
April, 1999 Guidance Manual from EPA:
“Use an alternative or supplemental
disinfectant or oxidant such as chloramines
or chlorine dioxide that will produce fewer
DBPs (Disinfectant Byproducts).”
“Monochloramine, and chlorine dioxide are
typically used to maintain a disinfectant
residual in the distribution system”
Chem 6A Michael J. Sailor, UC San Diego
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Use of monochloramine in water
purification
Chlorine:
Cl2 + H2O → HOCl
Monochloramine:
+ H+ + Cl-
NH3 + HOCl → NH2Cl + H2O
• Monochloramine kills bacteria too
• Not as strong an oxidant as chlorine or hypochlorite
• Produces fewer potentially toxic or carcinogenic
byproducts
Chem 6A Michael J. Sailor, UC San Diego
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Presence of lead in simulated
drinking water
2 months after
switching to
chloramine
disinfectant
water disinfected
with chlorine
Rebecca Renner, ENVIRONMENTAL SCIENCE & TECHNOLOGY JUNE 15, 2004
Chem 6A Michael J. Sailor, UC San Diego
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Chemistry of lead oxides
oxidation state: + 4
Hypochlorite reaction:
Pb + 2HOCl → PbO2 + 2HCl
Monochloramine reaction: oxidation state: + 2
Pb + NH2Cl + H2O → PbO + NH3 + HCl
Solubility in water: PbO: 0.017 g/L at 20 °C
Solubility of PbO2 << PbO
Chem 6A Michael J. Sailor, UC San Diego
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Acid-Base Behavior of Oxides
Some metal oxides and most metalloid oxides are
amphoteric (react with acid or base):
acid: Al2O3 + 6H+ → 2Al3+ + 3H2O
base: Al2O3 + 2OH- + 3H2O → 2Al(OH)4-
Chem 6A Michael J. Sailor, UC San Diego
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Acid-Base Behavior of Oxides
Metal oxides produce basic solutions in water:
MgO + H2O → Mg2+ + 2OH Because metals are ionic
Nonmetal oxides produce acidic solutions:
CO2 + H2O → HCO3- + H+
Because nonmetals are covalent
Chem 6A Michael J. Sailor, UC San Diego
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Acid-Base Behavior of Oxides
Metal oxides produce basic solutions in water:
PbO + H2O → Pb2+ + 2OH PbO2 + 2H2O → Pb4+ + 4OH Neither is very soluble in water, but PbO >> PbO2
Chem 6A Michael J. Sailor, UC San Diego
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Chemistry of lead oxides
“Changes in pH, drops in ORP, or both could
destabilize these PbO2 films, and thus increase
plumbosolvency…observations that have been
made by some water systems of erratic lead
release from lead service lines, and increases or
decreases without clear correlations with pH, DIC,
and temperature, may be caused at least in part by
effects of ORP changes.” --Lytle, D.A. and
Schock, M.R., U.S. Environmental Protection
Agency, 2005
ORP = oxidation-reduction potential
DIC = dissolved inorganic carbon
Chem 6A Michael J. Sailor, UC San Diego
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Periodic Trends
Main Points:
Quantum numbers summary
Electron configurations for d-block elements:
– First-in, first-out for transition metals: ns
electrons removed before (n-1)d electrons
– Magnetic properties of transition metal ions:
paramagnetism, diamagnetism
Chem 6A Michael J. Sailor, UC San Diego
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Measurement of Magnetic
Fig 8.19
Properties
No unpaired
electrons in
compound
Compound
has unpaired
electrons
Chem 6A Michael J. Sailor, UC San Diego
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Problem: Predicting Diamagnetism or
Paramagnetism from Electron
Configurations
2+
Possible electron configurations for the paramagnetic ion Fe are
given below. Which is correct?
(a)
(b)
(c)
(d)
(e) None of the above are correct
Chem 6A Michael J. Sailor, UC San Diego
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Solution: Predicting Diamagnetism or
Paramagnetism from Electron
Configurations
Electron configuration for Fe:
4s23d6
Electron configuration for Fe2+:
3d6
Always remove (n+1)s electrons before nd electrons when you
make ions.
How to place electrons in the d orbital? Follow Hund’s rule:
Chem 6A Michael J. Sailor, UC San Diego
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Solution: Predicting Diamagnetism or
Paramagnetism from Electron
Configurations
So (c) is the correct answer:
Fe2+
How many unpaired electrons in Fe2+?
4
Chem 6A Michael J. Sailor, UC San Diego
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