lecture 3: 123.101
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Transcript of lecture 3: 123.101
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Unit One Parts 3 & 4:molecular bonding
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Unit OneParts3&4
Locating electronsDescribing bondsShape of molecules
Pages 34 & 43
H O H3C BrHO
CH3Br
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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
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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
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what are bonds?
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Na Cl
Ionic bonds
Na Cl
Pg34
here we have an atom of sodium (Na)
and an atom of chlorine (Cl)
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Na Cl
Ionic bonds
Na Cl
Pg34
if we take one electron from Na and
give it to Cl...
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ClNa
Ionic bonds
Na+ Cl-
Pg34
we get 2 charged species (cation = positive charge & anion = negative charge)
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Na+
Ionic bonds
Cl-
NaCl
Pg34
opposite charges attract and give us an
ionic bond
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covalent bondsH H
Pg34
if we bring 2 atoms together and they...
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covalent bondsH H
Pg34
share their 2 electrons we have a
covalent bond
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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
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covalent bondsH H
H H
2electrons per bond Pg
34
please remember that this line is
2 electrons
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chemistrya pain
these areextremes just
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reality is in the middle
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where do we find electrons?
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ONE DOES NOT SIMPLY
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Aufbau Principle
lowest energy orbital
THIS IS THE LONG VERSION...NOT THE
VERSION I DO IN THE LECTURES
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Aufbau Principle
lowest energy orbital
don’t worry about the name...just that
electrons like to have lowest energy
possible...
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rather like many students...
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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
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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
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Pauli Exclusion Principle
no two electrons are identical
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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
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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)
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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
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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
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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
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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)
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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...
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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...
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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
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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??
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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!)
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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...
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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
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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...
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that's a lot of electrons...
luckily we don’t care about all them...
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all you have toremember is...
©jaci XIII@flickr
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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=
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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
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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.
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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)
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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)
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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)
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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!
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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...
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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’
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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
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what do valence electrons tell us?
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the number of bonds
H
OHH H
1 2
34
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the shape of molecules
109°
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how?
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Ne
1s22s22p6
noble gas
atoms are happy if they
have a full valence shell...
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Ne
1s22s22p6
noble gas
...commonly this means 8
electrons
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8 fullshellelectrons
Ne
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C
1s22s22p24 bonds
N
1s22s22p33 bonds
O
1s22s22p42 bonds Pg
36
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C
1s22s22p2
4 valence
electrons
Pg45
so for carbon to get to 8 it needs 4 more electrons
Pg45
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Pg46 4 bonds
Cor 4 new
covalent bonds
Pg46
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C
1s22s22p24 bonds
N
1s22s22p33 bonds
O
1s22s22p42 bonds Pg
36
nitrogen has 5 valence
electrons...so needs 3 more...
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N
1s22s22p3
5 valence
electrons
Pg46
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Pg46 3 bonds
Nso forms 3
covalent bonds
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C
1s22s22p24 bonds
N
1s22s22p33 bonds
O
1s22s22p42 bonds Pg
36
oxygen needs 2 more electrons so forms 2 covalent
bonds
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O
1s22s22p4 Pg46
6 valence
electrons
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O
Pg46 2 bonds
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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!
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8Octet rule: 8 valence electrons
CHH
HH
Pg36
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8Octet rule: 8 valence electrons
Pg37/46
CHN
HH O
H
H
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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
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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...
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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
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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
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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
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Acetone CH3COCH3
C + + 6HO3
Pg44
how do we deal with more complex
molecules?
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CC C
O
HH
H
HH
H
Acetone CH3COCH3
C + + 6HO3
Pg44
first draw all the atoms where you think
they might go...
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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...
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CC
C
O
H
HHH
H H
Acetone CH3COCH3
C + + 6HO3
Pg44
the central C and O both have only 7
valence electrons...
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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)
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Borohydride anion BH4––
Pg44
what happens if we have a negative
charge (anion)?
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B + 3H + H
Borohydride anion BH4––
Pg44
take the atoms as normal and...
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B + 3H + H
Borohydride anion BH4––add electron
Pg44
...add an electron
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B + 3H + H
Borohydride anion BH4––add electron
BHH
HH H B
H
H
H
≡
Pg44
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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?
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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)
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Ammonium cation NH4++lose electron
Pg44
if we have a positive charge (cation) we do the opposite...
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N + 3H + H
Ammonium cation NH4++lose electron
Pg44
start with our normal atoms...
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N + 3H + H
Ammonium cation NH4++lose electron
Pg44
then remove an electron
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NHH
HH H N
H
H
H
≡N + 3H + H
Ammonium cation NH4++lose electron
Pg44
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where is the charge?
is it on one atom?
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all over the molecule...
No, its all over the molecule! But...
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but the truth isn't useful, so...
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formal charges localise charge on an atom...
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formal charges localise charge on an atom...
this is ‘electron book-keeping’...we are just
assigning charge to one atom to help explain
chemistry...
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formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
...on an atom
Pg47
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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
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formal charge
(fc)=
number of valence
electrons–
number of unshared electrons
–½ number of shared electrons
...in lone pairs...
Pg47
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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
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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
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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
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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)
![Page 101: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/101.jpg)
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
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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
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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
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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
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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
![Page 106: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/106.jpg)
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
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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
![Page 108: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/108.jpg)
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)
![Page 109: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/109.jpg)
a bond
is 2electrons
O
OH
![Page 110: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/110.jpg)
a bond
is 2electrons
![Page 111: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/111.jpg)
simple model
![Page 112: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/112.jpg)
quantum model more accurate...
![Page 113: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/113.jpg)
Atomic orbitalsit's a quantum world...
we’ve looked at a nice simple model
so far...
![Page 114: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/114.jpg)
Atomic orbitalsit's a quantum world...
mathematicians and physicists have shown it’s a bit more complicated in ‘reality’
![Page 115: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/115.jpg)
but I don't like maths...
so...here's some pretty pictures...
![Page 116: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/116.jpg)
90%atomic orbital
Pg36
atomic orbital is the volume of space in which there is a 90% chance of
finding an electron
![Page 117: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/117.jpg)
2atomic orbital
electrons Pg37
remember: a maximum of 2 electrons per
orbital
![Page 118: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/118.jpg)
2sPic: Dr. Jonathan Gutow
Pg38
a 1s orbital is also a sphere...just a
lot smaller
![Page 119: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/119.jpg)
2sPic: Dr. Jonathan Gutow
Pg38
let’s ignore this nasty little effect
of maths...
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x
y
zpx
x
y
zpy
x
y
zpz
2p Pg38
![Page 121: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/121.jpg)
x
y
zpx
x
y
zpy
x
y
zpz
2p each of the three 2p orbitals is
dumbbell shaped... Pg
38
![Page 122: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/122.jpg)
x
y
zpx
x
y
zpy
x
y
zpz
2p ...they are identical in all ways except... Pg
38
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x
y
zpx
x
y
zpy
x
y
zpz
2p ...they point in different directions (hence the names) Pg
38
![Page 124: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/124.jpg)
x
y
zpx
x
y
zpy
x
y
zpz
2p Pg34
this is one orbital (just has two different
coloured areas)
![Page 125: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/125.jpg)
afraid?
![Page 126: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/126.jpg)
you will be...
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what is a bond?
our simple Lewis model helps explain a lot of chemistry...especially
reactions...
![Page 128: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/128.jpg)
what is a bond?
...but it fails to explain such fundamental
concepts as shape...
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what is a bond?
...actually, it can explain shape if we use VSEPR theory...but anyways, lets use those orbitals
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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)
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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...
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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...
![Page 133: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/133.jpg)
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)
![Page 134: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/134.jpg)
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
![Page 135: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/135.jpg)
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
![Page 136: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/136.jpg)
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!
![Page 137: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/137.jpg)
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)
![Page 138: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/138.jpg)
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)
![Page 139: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/139.jpg)
energy
σ*
σC•2py
C•2pyC–C
single (σ) bondPg38
if we take two 2p orbitals and combine them head-to-head
![Page 140: lecture 3: 123.101](https://reader035.fdocuments.us/reader035/viewer/2022062312/555d0930d8b42ab2228b4670/html5/thumbnails/140.jpg)
energy
σ*
σC•2py
C•2pyC–C
single (σ) bondPg38
...we get a sigma σ bonding
orbital...it is still like a cylinder...
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energy
σ*
σC•2py
C•2pyC–C
single (σ) bondPg38
...this is the normal single
bond we observe in alkanes etc.
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energy
σ*
σC•2py
C•2pyC–C
single (σ) bondPg38
this is one orbital NOT three
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single (σ) bond
Pg35
the blue bit is the sigma orbital...ignore
the red orbitals for the time being...
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single bond
σ (sigma) bond
C Cor the simple
version...THIS IS ALL YOU NEED TO KNOW
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single bond
σ (sigma) bond
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single bond
σ (sigma) bond
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Csp3
Pg38
an atom with 4 σ bonds is called an sp3 atom (as 1 x s and 3 x
p used in bonding)
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sp3 1
243
YOU NEED TO KNOW THIS
4 points
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tetrahedral
sp3
109°
BrC
BrHH
Pg41
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tetrahedral
sp3
109°
BrC
BrHH
Pg41
sp3 atoms are tetrahedral in shape
(the bonds stay as far apart as possible)
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tetrahedral sp3
maximum separation of four pointsmaximum separation of four valence electron pairs
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energy
carbon2pz
carbon2pz
C=Cπ*
C=Cπ
C C
C C
double (σ + π) bonds Pg38
two 2p orbitals can combine side-to-side
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energy
carbon2pz
carbon2pz
C=Cπ*
C=Cπ
C C
C C
double (σ + π) bonds Pg38
the new bond is a pi π bond
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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
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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)
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double (π) bond
Pg38
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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
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double (π) bond
Pg35
remember: this is ONE orbital (just two different
coloured halves)
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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
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no
rotation
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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)...
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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
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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
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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
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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?
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double bond
π (pi) bond
or the simple version...
THIS IS ALL YOU NEED TO KNOW
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double bond
π (pi) bond
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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)
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sp2
3 points
32
1
1 double bond and 2 single bonds and we
have an sp2 atom
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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
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trigonal planarsp2
Pg41
maximum separation of three pointsmaximum separation of three valence electron pairs
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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)
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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)
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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)
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sp2
points
1 2
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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
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linearsp
maximum separation of two pointsmaximum separation of two valence electron pairs
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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...
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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
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OCH3
CO2HH3C
O
H
H
O
OOH
OH
dynemicin A
sp2trigonal planar
sp3tetrahedralPg
40
...only three groups so sp2 and flat, trigonal
planar
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OCH3
CO2HH3C
O
H
H
O
OOH
OH
dynemicin A
splinear
sp2trigonal planar
sp3tetrahedralPg
40
straight line, two groups must be sp
and linear
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OCH3
CO2HH3C
O
H
H
O
OOH
OH
dynemicin A
what is oxygen?
Pg40
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OCH3
CO2HH3C
O
H
H
O
OOH
OH
dynemicin A
what is oxygen?
Pg40
...is it sp as attached to two carbon atoms?
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HO
H
sp, sp2 or sp3?
look at a simpler system...water, sp,
sp2 or sp3?
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sp, sp2 or sp3?
OHH
draw Lewis structure...
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sp, sp2 or sp3?
OHH we have FOUR
groups around O, two lone pairs &
two H atoms. So it is...
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HO
H
tetrahedral
sp3
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HO
H
tetrahedral
sp3that is why we draw
water as a bent molecule...its shape
is based on a tetrahedron...
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HO
H
tetrahedral
sp3...any atom with
four atoms or lone pairs around it is sp3 with all that
entails!
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sp, sp2 or sp3?
OC
HHwhat kind of atom
is the oxygen?
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1 double bondOC
HH
...and two lone pairs, so three
groups around the oxygen so it is...
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trigonal planar
sp2OC
HH
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sp, sp2 or sp3?
HCN what kind of atom is the nitrogen?
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1 triple bond
HCN and one lone pair so two groups so it
is...
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spHCNlinear
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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
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