Trends in the periodic table
http://www.meta-synthesis.com/webbook/35_pt/pt2.html
A Periodic Table
http://www.theodoregray.com/PeriodicTable/
1
O
Se
Po
Te
S
Oxygen Chemistry
2
Oxygen Chemistry (Energy)
How does a PEM (Proton Exchange Membrane) Fuel Cell Work?
80° C
2(H2
2H+ + 2e-)
O2 + 4H+ + 4e-
2H2O +
3
Glove boxes
Gloveboxes
4
Sulphur chemistry (allotropes)
Sulphur chemistry (allotropes)
S2
S3
S4
cyclo-S5
cyclo-S6
cyclo-S6.cyclo-S10 adduct
cyclo-S7
cyclo-S8
cyclo-S8
cyclo-S8
catena-Sx
catena-Sx
disulfur
trisulfur
tetrasulfur
cyclo-pentasulfur
ρ-sulfur
cyclo-Sn n = 9-15, 18, 20
cyclo-(nona; deca; undeca; dodeca; trideca; tetradeca;
pentadeca; octadeca; eicosa)sulfur
insoluble sulfur
φ-sulfur
ω-sulfur
λ-sulfur
µ-sulfur
π-sulfur
S-II, S-III, S-IV, S-V and
others
High pressure forms of αsulfur
α-, β-, γ-, δ- cycloheptasulfur
α-sulfur
β-sulfur
γ-sulfur
fibrous (ψ) sulfur
lamina sulfur
5
Sulphur chemistry (allotropes)
Sulphur chemistry (rocks)
6
Sulphur chemistry (rocks)
7
Sulphur chemistry (acid)
Sulphur chemistry (acid)
8
Chose Your Topic
Why are speed skaters in so much pain while
racing?
Why does roast garlic not taste like garlic?
How does life in deep sea vents work?
How can Saskatchewan solve arsenic poisoning in
Bangledesh?
How do you poison
someone with Po?
Molecular orbital theory
H&S 2.3
• looks at the whole molecule, with all participating nuclei fixed in their actual positions
• molecular orbitals (MO) are regions of space spread over the entire molecule that a
single electron might occupy
• each MO for a molecule arises from interactions between atomic orbitals of the
components of the molecule, which are:
H&S Fig 2.3, p.34
• first draw the orbital interaction diagram, then place electrons according to Aufbau
9
Which orbital overlap would give the strongest bond?
a)
b)
c)
d)
e)
2s to 2pz
2s to 2px
3d to 4d
2s to 4s
2s to 2s
Which orbital overlap would give the second strongest bond?
a)
b)
c)
d)
e)
2s to 2pz
2s to 2px
3d to 4d
2s to 4s
2s to 2s
10
Applying MO theory to other simple homonuclear diatomics
• He(g) is monomeric. Why doesn’t it give a diatomic molecule like H2(g)?
energy
• Recall we said alkali elements form homonuclear
diatomic molecules in vapour phase:
H&S Fig 2.5a, p.35
H&S Fig 2.5b, p.35
Molecular orbital theory
• Other features of the MO picture for bonding in H2:
H&S Fig 2.4, p.35
11
Which is the correct electron configuration of F?
1s
1s
1s
F2
1s
1s
12
O2,
1s
1s
13
N2
1s
1s
14
F2
O2
N2
• bond order
• bond strength
• magnetism
• MO
O2
15
Magnetism
• Diamagnetism
• Paramagnetism
• Ferromagnetism
16
Bonding and anti-bonding σ and σ* molecular orbitals
arising from p atomic orbitals
Bonding σ molecular orbital arising from p
atomic orbitals
17
Bonding and anti-bonding π and π* molecular
orbitals arising from p atomic orbitals
Bonding π molecular orbitals arising from p
atomic orbitals
18
NO+
CO
19
20
Group 15 (Pnictogens)
P
N
Sb
As
Bi
Nitrogen
21
Bonding in N2
Phosphorus
to memorise
not required to memorise
structure, but should recognise
22
Arsenic, Antimony
Bismuth
23
Group 14
N
Allotropes of Carbon
2 nm
2 nm
Prof. Dr. F. J. Giessibl Faculty of Physics Uniiversity of Regensburg
24
Carbon is Organic Chemistry
25
Oxides of carbon and silicon
C(s) + O2(g) –––> CO2(g)
O
C
Si(s) + O2(g) –––> SiO2(s)
O
O
160 ppm
e.g. px, py
O
O
~144°
Si
O
Silicates
• Minerals and synthetic materials comprised of silicate ions such as [SiO4]4–, in which
the lattice structures are completed with a huge range of different cations.
26
Pores contain water and counterions to balance the charge
Group 14 halides
F
F
F
F
F
F
Sn
F
F
F
F
Sn
FF
Sn
F
F
Sn
F
F
27
Silicones
• Prepared by hydrolysis of R2SiCl2 (R is usually methyl, CH3)
Si
Si
O
Si
O
n
Si
O
• Higher thermal, chemical and O2 stability than carbon-based organic ploymers
Bond strength: Si-O > C-C by ~90 kJ/mol (30%)
Silicon
28
Conductors, Semiconductors, Insulators
Conductors, Semiconductors, Insulators
29
Conductors, Semiconductors, Insulators
Band gap energies (eV)
Group 14
C
Group13-15 Compound Semiconductors
5.4
AlN 6.3
GaN 3.2
InN 2.1
Si 1.1
AlP 3.0
GaP 2.25
InP 1.27
Ge 0.72
AlAs 2.3
GaAs 1.34
InAs 0.33
Sn 0.08
AlSb 1.52
GaSb 0.70
InSb 0.18
increasing
bond
strength and
Eg
Group 12-16 Compound Semiconductors
CdS 2.45
ZnO 3.3
CdSe 1.47
CdTe 1.45
30
Discussed in class
-We have discussed previously how the LCAO gives rise to
MOs. When this is extended to larger number of atoms (on the
mole scale), the energy gap between each MO becomes
infinitesimally small and the collection of MOs can be treated
as a band. The gap between the bonding and antibonding
orbitals becomes known as the band gap. When there is no
gap, the material is a conductor (ie all metals). When there is a
gap of ca. 1eV to 3 eV (energy of visible light), the material is
known as a intrinsic semiconductor and with a bandgap of
greater than 3 eV, it is an insulator.
Band gap energies (eV)
Group 14
C
Group13-15 Compound Semiconductors
5.4
AlN 6.3
GaN 3.2
InN 2.1
Si 1.1
AlP 3.0
GaP 2.25
InP 1.27
Ge 0.72
AlAs 2.3
GaAs 1.34
InAs 0.33
Sn 0.08
AlSb 1.52
GaSb 0.70
InSb 0.18
increasing
bond
strength and
Eg
Group 12-16 Compound Semiconductors
CdS 2.45
ZnO 3.3
CdSe 1.47
CdTe 1.45
31
Example Problem
Would you expect the band gap of GaSb to be greater or less
than the band gap of InSb?
GREATER, Ga is n=4 and therefore smaller than In, which is n=5
 Ga-Sb bond is shorter than In-Sb bond and therefore there is
a greater bond strength, therefore greater splitting between
bonding and antibonding orbitals, therefore greater bandgap.
What is the wavelength of the absorption edge for GaSb and
InSb and what do the absorption and band diagrams look
like?
Example Problem cont..
32
Extrinsic semiconductor
n-type semiconductor
• A semiconductor doped with a supervalent element (ie Si doped with P
shown below). The doping introduces extra electrons as charge carriers
(one charge carrier for every atom of dopant). The electrons have an
energy level just below that of the conduction band.
p-type semiconductor
• A semiconductor doped with a subvalent element (ie Si doped with B
shown below). The doping introduces extra holes as charge carriers
(one charge carrier for every atom of dopant). These holes are positive
charge carriers, hence the “p”.
33
N
Germanium
Germanium is also a semiconductor,
Also, recall that we know many properties of Germanium
from our first class
eka-silicon
germanium
72 g/mol
72.59 g/mol
5.5 g/cm3
5.36 g/cm3
“high” m.p.
m.p. = 958 °C
Es forms EsO2 which
has high m.p. and ρ
= 4.7 g/cm3
Ge forms GeO2
m.p. = 1100 °C
and ρ = 4.70 g/cm3
EsCl4 volatile liquid
with b.p. < 100°C
and ρ = 1.9 g/cm3
GeCl4 volatile liquid
with b.p. 83°C
and ρ = 1.88 g/cm3
34
Tin
Lead
35
N
Group 13
36
Aluminium is a light structural metal
M.P. of Gallium is 29.8 C
37
Some properties of the group 13 elements and their ions
Rules for Determining Molecular Shape: Valance Shell Electron Pair-Repulsion
Model
38
Same information (slightly different images)
39
Same information (slightly different images)
40
Boron halides
• With just three valence electrons, boron and aluminum do not achieve a full octet in
their trivalent covalent compounds.
delocalized π-system
-bonds
F
F
F
F B
F
F
B
B
F
F
F
F
B
F
F
sp2-hybridized boron
F
sp3-hybridized boron
131 pm
B
F
F
145 pm
F
L
X
B
L
X
B
X
X
X
X
Quick Review of Acids
Arrhenius Acid:
Arrhenius Base:
Bronstead-Lowry Acid:
Bronstead-Lowry Base :
Lewis Acid:
Lewis Base:
L
X
X
B
X
L
B
X
X
X
41
Aluminum halides
F
Al
F
F
F
F
F
Al
F
F
F
F
F
F
Al
F
F
F
H&S, Fig 13.14, p. 344
Boron and rockets
42
Boron and rockets (cont’d)
• There are many more boranes, which are larger clusters of boron with hydrogen
interspersed.
Boron and rockets (cont’d)
• Other binary compounds of boranes, including boron nitride (BN) and boron carbide
(B4C), are hard, high melting, and chemically resistant.
e.g. materials used for rocket nose cones!
• Boron carbide is actually B12C3, in which icosahedra of pure boron are linked
together via the carbons in the extended solid state structure.
• Boron nitride (sublimation point 2603K)
Long B-N
short B-N
43
Anodisation of Aluminium
44