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lecture 3 of 123.101 chemistry and living systems
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Unit One Parts 3 & 4:molecular bonding
Unit OneParts3&4
Locating electronsDescribing bondsShape of molecules
Pages 34 & 43
H O H3C BrHO
CH3Br
Unit OneParts3&4
Locating electronsDescribing bondsShape of molecules
Pages 34 & 43
H O H3C BrHO
CH3Br
if we know where electrons are we can
predict reactions and shape...they really are key to understanding
chemistry
Unit OneParts3&4
Locating electronsDescribing bondsShape of molecules
Pages 35 & 45
H O H3C BrHO
CH3Br
as I’ve taken the material out of order,
I’ll give you some page numbers
what are bonds?
Na Cl
Ionic bonds
Na Cl
Pg34
here we have an atom of sodium (Na)
and an atom of chlorine (Cl)
Na Cl
Ionic bonds
Na Cl
Pg34
if we take one electron from Na and
give it to Cl...
ClNa
Ionic bonds
Na+ Cl-
Pg34
we get 2 charged species (cation = positive charge & anion = negative charge)
Na+
Ionic bonds
Cl-
NaCl
Pg34
opposite charges attract and give us an
ionic bond
covalent bondsH H
Pg34
if we bring 2 atoms together and they...
covalent bondsH H
Pg34
share their 2 electrons we have a
covalent bond
covalent bondsH H
H H
2electrons per bond Pg
34
this is the bond we’ll be dealing with most often and is represented by
the black line
covalent bondsH H
H H
2electrons per bond Pg
34
please remember that this line is
2 electrons
chemistrya pain
these areextremes just
reality is in the middle
where do we find electrons?
ONE DOES NOT SIMPLY
Aufbau Principle
lowest energy orbital
THIS IS THE LONG VERSION...NOT THE
VERSION I DO IN THE LECTURES
Aufbau Principle
lowest energy orbital
don’t worry about the name...just that
electrons like to have lowest energy
possible...
rather like many students...
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
2s 2px 2py 2pz
1s
energy
hydrogen1s1
1H
Pg43
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
2s 2px 2py 2pz
1s
energy
hydrogen1s1
1H
Pg43
just one electron so in first orbital
Pauli Exclusion Principle
no two electrons are identical
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
2s 2px 2py 2pz
1s
energy
helium1s2
2He
Pg43
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
2s 2px 2py 2pz
1s
energy
helium1s2
2He
Pg43
one electron has spin +½ (up) and the other
spin –½ (down)
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
2s 2px 2py 2pz
1s
energy
helium1s2
2He
Pg43
doesn’t matter what it means...just remember an electron can only be
up or down
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
2s 2px 2py 2pz
1s
energy
helium1s2
2He
Pg43
so can only ever have two electrons
per orbital
1s
2s
2px 2py 2pz
energy
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
3Li
lithium1s22s1
Pg43
1s
2s
2px 2py 2pz
energy
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
3Li
lithium1s22s1
Pg43
lithium obeys both rules...fill lowest orbital first (until full) then fill
next lowest)
1s
2s
2px 2py 2pz
energy
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
4Be
beryllium1s22s2
Pg43
...adding one more electron is easy...
1s
2s
2px 2py 2pz
energy
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
5B
boron1s22s22p1
Pg43
...and another...
1s
2s
2px 2py 2pz
energy
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
5B
boron1s22s22p1
Pg43
it could go in any of 2px, 2py or 2pz,
they’re identical...well energetically they are
1s
2s
2px 2py 2pz
energy
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
5B
boron1s22s22p1
Pg43
but, where does the next (and most
important as its carbon) go??
Hund's rule
electrons as far apart as p o s s i b l e
(degenerate orbitals )(as long as it doesn’t
violate any of the previous rules!)
Hund's rule
electrons as far apart as p o s s i b l e
(degenerate orbitals )
makes sense as like charges always
repel...
1s
2s
2px 2py 2pz
energy
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
6C
carbon
1s22s22px12py1
1s22s22p2
Pg43
1s
2s
2px 2py 2pz
energy
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
6C
carbon
1s22s22px12py1
1s22s22p2
Pg43
could be 2pz, makes no
difference...
that's a lot of electrons...
luckily we don’t care about all them...
all you have toremember is...
©jaci XIII@flickr
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
6C
Pg45
carbon1s22s22p2
atomic number
number of electrons=
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
6C
carbon
1s22s22px12py1
1s22s22p2
1s
2s
2px 2py 2pz
energy
Valence electrons
Pg43
1 18
H 2 13 14 15 16 17 He
Li Be B C N O F Ne
Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
6C
carbon
1s22s22px12py1
1s22s22p2
1s
2s
2px 2py 2pz
energy
Valence electrons
Pg44
only need consider high energy electrons or those on the outside called the
valence electrons.
C C
1s22s22p2 2s22p2
N N
1s22s22p3 2s22p3
group 1 2 13 14 15 16 17 18
H He
Li Be B C N O F Ne Pg44
if we consider the Bohr model of the atom, the
one where we think of an atom resembling a planet with moons orbiting (or
the solar system)
C C
1s22s22p2 2s22p2
N N
1s22s22p3 2s22p3
group 1 2 13 14 15 16 17 18
H He
Li Be B C N O F Ne Pg44
then the valence electrons are those on the outer edge (like Neptune
for young-upstarts or Pluto for us oldies)
C C
1s22s22p2 2s22p2
N N
1s22s22p3 2s22p3
group 1 2 13 14 15 16 17 18
H He
Li Be B C N O F Ne Pg44
then the valence electrons are those on the outer edge (like Neptune
for young-upstarts or Pluto for us oldies)
C C
1s22s22p2 2s22p2
N N
1s22s22p3 2s22p3
group 1 2 13 14 15 16 17 18
H He
Li Be B C N O F Ne Pg41
absolute rubbish...but more comprehendible!
C C
1s22s22p2 2s22p2
N N
1s22s22p3 2s22p3
group 1 2 13 14 15 16 17 18
H He
Li Be B C N O F Ne Pg41
an easy we to remember the number of valence electrons is
to take group number...
valence electrons 1 2 3 4 5 6 7 8
H He
Li Be B C N O F Ne
C C
1s22s22p2 2s22p2
N N
1s22s22p3 2s22p3
Pg41
...and ignore first ‘1’
valence electrons 1 2 3 4 5 6 7 8
H He
Li Be B C N O F Ne
C C
1s22s22p2 2s22p2
N N
1s22s22p3 2s22p3
Pg41
so oxygen (group 16) has
6 valence electrons
what do valence electrons tell us?
the number of bonds
H
OHH H
1 2
34
the shape of molecules
109°
how?
Ne
1s22s22p6
noble gas
atoms are happy if they
have a full valence shell...
Ne
1s22s22p6
noble gas
...commonly this means 8
electrons
8 fullshellelectrons
Ne
C
1s22s22p24 bonds
N
1s22s22p33 bonds
O
1s22s22p42 bonds Pg
36
C
1s22s22p2
4 valence
electrons
Pg45
so for carbon to get to 8 it needs 4 more electrons
Pg45
Pg46 4 bonds
Cor 4 new
covalent bonds
Pg46
C
1s22s22p24 bonds
N
1s22s22p33 bonds
O
1s22s22p42 bonds Pg
36
nitrogen has 5 valence
electrons...so needs 3 more...
N
1s22s22p3
5 valence
electrons
Pg46
Pg46 3 bonds
Nso forms 3
covalent bonds
C
1s22s22p24 bonds
N
1s22s22p33 bonds
O
1s22s22p42 bonds Pg
36
oxygen needs 2 more electrons so forms 2 covalent
bonds
O
1s22s22p4 Pg46
6 valence
electrons
O
Pg46 2 bonds
C
1s22s22p24 bonds
N
1s22s22p33 bonds
O
1s22s22p42 bonds Pg
34
hopefully, you can see this is where those magic numbers in lecture one came
from!
8Octet rule: 8 valence electrons
CHH
HH
Pg36
8Octet rule: 8 valence electrons
Pg37/46
CHN
HH O
H
H
C + + 4HO
+ F FH ≡ H F
Lewis structures
Hydrofluoric acid HF
Methanol CH3OH
H
CH
HH O H ≡ H C
H
O
H
H
use octet rule to draw the structure of stable
molecules...
Pg37/46
Pg41
C + + 4HO
+ F FH ≡ H F
Lewis structures
Hydrofluoric acid HF
Methanol CH3OH
H
CH
HH O H ≡ H C
H
O
H
H
H–F easy..H = 2 electrons (full s
orbital) & F = 8...
Pg37/46
C + + 4HO
+ F FH ≡ H F
Lewis structures
Hydrofluoric acid HF
Methanol CH3OH
H
CH
HH O H ≡ H C
H
O
H
H
Lewis structure shows all valence electrons represented by our
simple diagram H–F
C + + 4HO
+ F FH ≡ H F
Lewis structures
Hydrofluoric acid HF
Methanol CH3OH
H
CH
HH O H ≡ H C
H
O
H
H
works for more complex
molecules
Pg37/46
C + + 4HO
+ F FH ≡ H F
Lewis structures
Hydrofluoric acid HF
Methanol CH3OH
H
CH
HH O H ≡ H C
H
O
H
H
Note: it helps to leave lone pairs (of electrons)
on diagram...this is where a lot of chemistry
occurs...
Pg37/46
Acetone CH3COCH3
C + + 6HO3
Pg44
how do we deal with more complex
molecules?
CC C
O
HH
H
HH
H
Acetone CH3COCH3
C + + 6HO3
Pg44
first draw all the atoms where you think
they might go...
Acetone CH3COCH3
C + + 6HO3
CC
CH
HHH
H H
O
Pg44
now join all the atoms together...some of the
atoms have full valence shells so we
can draw them in as on the next slide...
CC
C
O
H
HHH
H H
Acetone CH3COCH3
C + + 6HO3
Pg44
the central C and O both have only 7
valence electrons...
CC
C
O
H
HHH
H H
Acetone CH3COCH3
C + + 6HO3
H3CC
CH3
O ≡O
Pg44
...but if they share 4 electrons they both have 8 valence electrons...this gives us a double bond
(alkene)
Borohydride anion BH4––
Pg44
what happens if we have a negative
charge (anion)?
B + 3H + H
Borohydride anion BH4––
Pg44
take the atoms as normal and...
B + 3H + H
Borohydride anion BH4––add electron
Pg44
...add an electron
B + 3H + H
Borohydride anion BH4––add electron
BHH
HH H B
H
H
H
≡
Pg44
B + 3H + H
Borohydride anion BH4––add electron
BHH
HH H B
H
H
H
≡
Pg44
does it matter which atom we give
the electron to?
B + 3H + H
Borohydride anion BH4––add electron
BHH
HH H B
H
H
H
≡
Pg44
does it matter which atom we give
the electron to?
no! (but in this case H– makes more chemical sense)
Ammonium cation NH4++lose electron
Pg44
if we have a positive charge (cation) we do the opposite...
N + 3H + H
Ammonium cation NH4++lose electron
Pg44
start with our normal atoms...
N + 3H + H
Ammonium cation NH4++lose electron
Pg44
then remove an electron
NHH
HH H N
H
H
H
≡N + 3H + H
Ammonium cation NH4++lose electron
Pg44
where is the charge?
is it on one atom?
all over the molecule...
No, its all over the molecule! But...
but the truth isn't useful, so...
formal charges localise charge on an atom...
formal charges localise charge on an atom...
this is ‘electron book-keeping’...we are just
assigning charge to one atom to help explain
chemistry...
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
...on an atom
Pg47
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons...according to
the atoms position in the periodic table
Pg47
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
...in lone pairs...
Pg47
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
...or the number of bonds to that
atom
Pg47
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
N + 3H NHH
HH+ H
N fc = 5-0-½(8)=+1
H N
H
H
H
≡cation
Pg47
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
N + 3H NHH
HH+ H
N fc = 5-0-½(8)=+1
H N
H
H
H
≡cationno charge on H as:
H = 1-0-½(2) = 0
Pg47
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
– number of bonds
N + 3H NHH
HH+ H
N fc = 5-0-4=+1
H N
H
H
H
≡cation
Pg47
the simplified formula (just use number of bonds)
O O O+ + O OO
O OO
≡O3ozone
neutral
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
Pg47
O O O+ + O OO
O OO
≡O3ozone
neutral
lhs O; fc = 6-4-½(4)=0
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
Pg47
O O O+ + O OO
O OO
≡O3ozone
neutral
lhs O; fc = 6-4-½(4)=0 central O; fc = 6-2-½(6)=+1rhs O; fc = 6-6-½(2)=-1
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
Pg47
O O O+ + O OO
O OO
≡O3ozone
neutral
lhs O; fc = 6-4-½(4)=0 central O; fc = 6-2-½(6)=+1rhs O; fc = 6-6-½(2)=-1
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
Pg47
O OO
≡atom's formal
charges
O O O+ + O OO
O OO
≡O3ozone
neutral
lhs O; fc = 6-4-½(4)=0 central O; fc = 6-2-½(6)=+1rhs O; fc = 6-6-½(2)=-1
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
Pg47
O OO
≡atom's formal
charges
O O O+ + O OO
O OO
≡O3ozone
neutral
lhs O; fc = 6-4-½(4)=0 central O; fc = 6-2-½(6)=+1rhs O; fc = 6-6-½(2)=-1
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
ozone neutral as + & – cancel each
other out
Pg47
O OO
≡atom's formal
charges
O O O+ + O OO
O OO
≡O3ozone
neutral
lhs O; fc = 6-4-½(4)=0 central O; fc = 6-2-½(6)=+1rhs O; fc = 6-6-½(2)=-1
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
these charges explain why ozone is so
reactive!
Pg47
O OO
≡atom's formal
charges
O O O+ + O OO
O OO
≡O3ozone
neutral
lhs O; fc = 6-4-2=0 central O; fc = 6-2-3=+1rhs O; fc = 6-6-1=-1
formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
– number of bonds
Pg47
the simplified formula (just use number of bonds)
a bond
is 2electrons
O
OH
a bond
is 2electrons
simple model
quantum model more accurate...
Atomic orbitalsit's a quantum world...
we’ve looked at a nice simple model
so far...
Atomic orbitalsit's a quantum world...
mathematicians and physicists have shown it’s a bit more complicated in ‘reality’
but I don't like maths...
so...here's some pretty pictures...
90%atomic orbital
Pg36
atomic orbital is the volume of space in which there is a 90% chance of
finding an electron
2atomic orbital
electrons Pg37
remember: a maximum of 2 electrons per
orbital
2sPic: Dr. Jonathan Gutow
Pg38
a 1s orbital is also a sphere...just a
lot smaller
2sPic: Dr. Jonathan Gutow
Pg38
let’s ignore this nasty little effect
of maths...
x
y
zpx
x
y
zpy
x
y
zpz
2p Pg38
x
y
zpx
x
y
zpy
x
y
zpz
2p each of the three 2p orbitals is
dumbbell shaped... Pg
38
x
y
zpx
x
y
zpy
x
y
zpz
2p ...they are identical in all ways except... Pg
38
x
y
zpx
x
y
zpy
x
y
zpz
2p ...they point in different directions (hence the names) Pg
38
x
y
zpx
x
y
zpy
x
y
zpz
2p Pg34
this is one orbital (just has two different
coloured areas)
afraid?
you will be...
what is a bond?
our simple Lewis model helps explain a lot of chemistry...especially
reactions...
what is a bond?
...but it fails to explain such fundamental
concepts as shape...
what is a bond?
...actually, it can explain shape if we use VSEPR theory...but anyways, lets use those orbitals
energy
H•1s
H•1s
H HH• + H•
single (σ) bond
Pg37
here we have 2 hydrogen atoms
(each with 1 electron in a 1s orbital)
σ*
σH–H
energy
H•1s
H•1s
H HH• + H•
single (σ) bond
Pg35
to form a covalent bond they must
share their electrons...
σ*
σH–H
energy
H•1s
H•1s
H HH• + H•
single (σ) bond
Pg35
...this is achieved by combining the
two atomic orbitals to give...
σ*
σH–H
energy
H•1s
H•1s
H HH• + H•
single (σ) bond
Pg35
...a new molecular orbital, a sigma σ orbital (or bond)
σ*
σH–H
energy
H•1s
H•1s
H HH• + H•
single (σ) bond
Pg35
...this bonding orbital is lower in energy than the
atoms...so a bond will form
σ*
σH–H
energy
H•1s
H•1s
H HH• + H•
single (σ) bond
Pg37
a consequence of the maths is we also get an
anti-bonding sigma orbital (σ*)...2 orbitals
must give 2 new orbitals
σ*
σH–H
energy
H•1s
H•1s
H HH• + H•
single (σ) bond
Pg37
...but lets ignore this confusing little devil for
the time being!
single (σ) bond
H HPg47
it is called a σ orbital as is symmetrical along
bond axis (you can rotate it like a cylinder and it
doesn’t change)
single (σ) bond
C• + H• C H
Pg37
all bonds to H are sigma (as all are like a
cylinder)...here we overlap 1s of H with 2p
of C and get sigma bond)
energy
σ*
σC•2py
C•2pyC–C
single (σ) bondPg38
if we take two 2p orbitals and combine them head-to-head
energy
σ*
σC•2py
C•2pyC–C
single (σ) bondPg38
...we get a sigma σ bonding
orbital...it is still like a cylinder...
energy
σ*
σC•2py
C•2pyC–C
single (σ) bondPg38
...this is the normal single
bond we observe in alkanes etc.
energy
σ*
σC•2py
C•2pyC–C
single (σ) bondPg38
this is one orbital NOT three
single (σ) bond
Pg35
the blue bit is the sigma orbital...ignore
the red orbitals for the time being...
single bond
σ (sigma) bond
C Cor the simple
version...THIS IS ALL YOU NEED TO KNOW
single bond
σ (sigma) bond
single bond
σ (sigma) bond
Csp3
Pg38
an atom with 4 σ bonds is called an sp3 atom (as 1 x s and 3 x
p used in bonding)
sp3 1
243
YOU NEED TO KNOW THIS
4 points
tetrahedral
sp3
109°
BrC
BrHH
Pg41
tetrahedral
sp3
109°
BrC
BrHH
Pg41
sp3 atoms are tetrahedral in shape
(the bonds stay as far apart as possible)
tetrahedral sp3
maximum separation of four pointsmaximum separation of four valence electron pairs
energy
carbon2pz
carbon2pz
C=Cπ*
C=Cπ
C C
C C
double (σ + π) bonds Pg38
two 2p orbitals can combine side-to-side
energy
carbon2pz
carbon2pz
C=Cπ*
C=Cπ
C C
C C
double (σ + π) bonds Pg38
the new bond is a pi π bond
energy
carbon2pz
carbon2pz
C=Cπ*
C=Cπ
C C
C C
double (σ + π) bonds Pg38
here we have a C–C σ bond and
a pi π bond
energy
carbon2pz
carbon2pz
C=Cπ*
C=Cπ
C C
C C
double (σ + π) bonds Pg38
the pi π bond is one orbital (with
two bits to it)
double (π) bond
Pg38
double (π) bond
Pg38
it is called a pi π orbital as rotation around the C–C
axis causes a change (from red to blue) so no longer
like a cylinder
double (π) bond
Pg35
remember: this is ONE orbital (just two different
coloured halves)
double (π) bond
Pg38
we have an inner σ bond (the rod) and an outer π
bond (the orbital) hence it is a double bond
no
rotation
H3C CH3
CH3
CH3
CH3
HO
H3C CH3
CH3
CH3 CH3
H
O
light isomerises complexedcis-retinal
multistep enzyme-catalysed reverse
process
Pg38
the p bond prevents alkenes from rotating (the two bonds can’t twist pass
each other)...
H3C CH3
CH3
CH3
CH3
HO
H3C CH3
CH3
CH3 CH3
H
O
light isomerises complexedcis-retinal
multistep enzyme-catalysed reverse
process
Pg38
this can effect shape of molecule
H3C CH3
CH3
CH3
CH3
HO
H3C CH3
CH3
CH3 CH3
H
O
light isomerises complexedcis-retinal
multistep enzyme-catalysed reverse
process
Pg38
we must break π bond before
alkene can rotate
H3C CH3
CH3
CH3
CH3
HO
H3C CH3
CH3
CH3 CH3
H
O
light isomerises complexedcis-retinal
multistep enzyme-catalysed reverse
process
Pg38
the change in shape initiates the visual cascade and
our sight
H3C CH3
CH3
CH3
CH3
HO
H3C CH3
CH3
CH3 CH3
H
O
light isomerises complexedcis-retinal
multistep enzyme-catalysed reverse
process
Pg38
why do you think red path is easy but blue hard?
double bond
π (pi) bond
or the simple version...
THIS IS ALL YOU NEED TO KNOW
double bond
π (pi) bond
sp2C
Pg38
an atom with three σ orbitals and one π
orbital is called an sp2 atom (we only count the orbitals used in making
s orbitals)
sp2
3 points
32
1
1 double bond and 2 single bonds and we
have an sp2 atom
trigonal planar
sp2120°Pg41
sp2 atoms are trigonal planar (flat and pointing to the
corners of a triangle)...again, this is because the orbitals
try to be as far apart as possible
trigonal planarsp2
Pg41
maximum separation of three pointsmaximum separation of three valence electron pairs
H C C Hσ
CH HCσ
σ
triple (σ + 2x π) bonds
π (2py + 2py)
π
π
π (2pz + 2pz)
Pg39
a triple bond (like an alkyne) is formed from one σ bond and two π bonds (at right angles to each other due to the direct of the p orbitals that made them)
H C C Hσ
CH HCσ
σ
triple (σ + 2x π) bonds
π (2py + 2py)
π
π
π (2pz + 2pz)
Pg39
so...two p orbitals combine head-to-head to give a σ bond
and two pairs of p orbitals combine side-to-side to give
the two π orbitals (& there are only two π orbitals)
spC
Pg39
an atom with two σ orbitals and two π orbitals
is called an sp atom (as two orbitals made the
basic σ skeleton)
sp2
points
1 2
linear
sp180°Pg40
an atom with two groups on it will be
linear (a straight line) as the orbitals stay as far apart as possible
linearsp
maximum separation of two pointsmaximum separation of two valence electron pairs
OCH3
CO2HH3C
O
H
H
O
OOH
OH
dynemicin A
Pg40
here is a real molecule...we should be able to identify the types
of atoms present...
OCH3
CO2HH3C
O
H
H
O
OOH
OH
dynemicin Asp3
tetrahedralPg40
four groups attached so it must be sp3 and as
those groups try to stay as far apart as possible
it is tetrahedral
OCH3
CO2HH3C
O
H
H
O
OOH
OH
dynemicin A
sp2trigonal planar
sp3tetrahedralPg
40
...only three groups so sp2 and flat, trigonal
planar
OCH3
CO2HH3C
O
H
H
O
OOH
OH
dynemicin A
splinear
sp2trigonal planar
sp3tetrahedralPg
40
straight line, two groups must be sp
and linear
OCH3
CO2HH3C
O
H
H
O
OOH
OH
dynemicin A
what is oxygen?
Pg40
OCH3
CO2HH3C
O
H
H
O
OOH
OH
dynemicin A
what is oxygen?
Pg40
...is it sp as attached to two carbon atoms?
HO
H
sp, sp2 or sp3?
look at a simpler system...water, sp,
sp2 or sp3?
sp, sp2 or sp3?
OHH
draw Lewis structure...
sp, sp2 or sp3?
OHH we have FOUR
groups around O, two lone pairs &
two H atoms. So it is...
HO
H
tetrahedral
sp3
HO
H
tetrahedral
sp3that is why we draw
water as a bent molecule...its shape
is based on a tetrahedron...
HO
H
tetrahedral
sp3...any atom with
four atoms or lone pairs around it is sp3 with all that
entails!
sp, sp2 or sp3?
OC
HHwhat kind of atom
is the oxygen?
1 double bondOC
HH
...and two lone pairs, so three
groups around the oxygen so it is...
trigonal planar
sp2OC
HH
sp, sp2 or sp3?
HCN what kind of atom is the nitrogen?
1 triple bond
HCN and one lone pair so two groups so it
is...
spHCNlinear
what have....we learnt?
•e l e c t r o n s where they are
•b o n d swhat they are
•s h a p e Courtesy: National Science Foundation
ReadPages 36, 41, 48-57
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