lecture 3: 123.101

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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