3.1 molecular orbitals

Question 1

can VSEPR explain the bonding in all compounds

Answer 1

no

Question 2

what can molecular theory provide an explanation for

Answer 2

more complex molecules

Question 3

when do molecular orbitals form

Answer 3

when atomic orbitals combine

Question 4

what is the number of molecular orbitals formed equal to

Answer 4

the number of atomic orbitals that combine

Question 5

what does the combination of two atomic orbitals result in

Answer 5

the formation of a bonding molecular orbital and an antibonding orbital

Question 6

what encompasses both nuclei in a molecular orbital

Answer 6

the bonding molecular orbital

Question 7

what forms the basis of bonding between atoms

Answer 7

the attraction of the positively charged nuclei and the negatively charged electrons in the bonding molecular orbital

Question 8

how many electrons max can each molecular orbital hold

Answer 8

2

Question 9

how are bonding molecular orbitals for non polar covalent bonds described

Answer 9

symmetrical about the mid point between two atoms

Question 10

what do polar covalent bonds result from

Answer 10

bonding molecular orbitals that are asymmetric about the midpoint between the two atoms

Question 11

which atom in an orbital has the greater share of bonding electrons

Answer 11

the one with the greater value for electronegativity

Question 12

how are ionic compounds described in relation to molecular orbitals

Answer 12

an extreme case of asymmetry, with the bonding molecular orbital being almost entirely located around just one atom, resulting in the formation of ions

Question 13

what are sigma bonds

Answer 13

the molecular orbitals that form by end on overlap of atomic orbitals along the axis of the covalent bonds

Question 14

what are pi bonds

Answer 14

the molecular orbitals that form by side on overlap of parallel atomic orbitals that lie perpendicular to the axis of the covalent bond

Question 15

what can electronic configuration of an isolated carbon atom not explain

Answer 15

the number of bonds formed by carbon atoms in molecules

Question 16

how can the bonding and shape of molecules of carbon be explained

Answer 16

by hybridisation

Question 17

what can hybridisation explain

Answer 17

the bonding and shape of molecules of carbon

Question 18

what is hybridisation

Answer 18

the processs of mixing atomic orbitals within an atom to generate a set of new atomic orbitals

Question 19

what are hybrid orbitals

Answer 19

the degenerate orbitals produced by hybridisation

Question 20

in alkanes, the 2s orbital and the three 2p orbitals of carbon hybridise to form…

Answer 20

four degenerate sp3 hybrid orbitals

Question 21

what do degenerate sp3 hybrid orbitals arrange in

Answer 21

a tetrahedral arrangement

Question 22

how do sp3 hybrid orbitals form sigma bonds

Answer 22

by overlapping end on with other atomic orbitals

Question 23

how can bonding in alkenes be explained

Answer 23

in terms of sp2 hybridisation

Question 24

how does hybridisation occur in alkenes

Answer 24

the 2s orbital and two of the 2p orbitals hybridise to form three degenerate sp2 hybrid orbitals

Question 25

what arrangement is adopted by sp2 hybrid orbitals

Answer 25

trigonal planar

Question 26

which bond type is formed by hybrid sp2 orbitals

Answer 26

sigma

Question 27

which bond type is formed by hybrid sp3 orbitals

Answer 27

sigma

Question 28

what happens to the remaining 2p orbital on each carbon atom of the double bond in alkenes when hybridisation occurs

Answer 28

remains unhybridised and lies perpendicular to the axis of the sigma bond

Question 29

which bond type is formed by the unhybridised p orbitals

Answer 29

pi

Question 30

how can the bonding in benzene and other aromatic systems be described in terms of

Answer 30

sp2 hybridisation

Question 31

how are the carbon atoms in benzene arranged

Answer 31

a cyclic structure with sigma bonds between the carbon atoms

Question 32

which bonds hold the carbon atoms together in a benzene ring

Answer 32

sigma

Question 33

what do the unhybridised p orbitals on each carbon atom in a benzene ring do

Answer 33

they overlap side on to form a pi molecular system, perpendicular to the plane of the sigma bonds

Question 34

how can the electrons in a benzene ring be described

Answer 34

delocalised

Question 35

how can the bonding in alkynes be explained

Answer 35

in terms of sp hybridisation

Question 36

what arrangement do the 2s and 2p orbitals of carbon adopt when they hydridise to form two degenerate hybrid orbitals

Answer 36

linear

Question 37

which bonds are formed when the hybrid sp orbitals overlap

Answer 37

sigma

Question 38

which bonds are formed when the unhybridised p orbitals overlap

Answer 38

pi

Question 39

what can molecular orbital theory be used to explain

Answer 39

why organic molecules are colourless or coloured

Question 40

what is the HOMO

Answer 40

the highest occupied molecular orbital

Question 41

what is the LUMO

Answer 41

the lowest unoccupied molecular orbital

Question 42

what is the highest occupied molecular orbital

Answer 42

the highest bonding molecular orbital containing electrons

Question 43

what do electrons leave when they fill bonding molecular orbitals

Answer 43

they leave higher energy antibonding orbitals unfilled

Question 44

what can cause electrons to be promoted from HOMO to LUMO

Answer 44

absorption of electromagnetic energy

Question 45

why do most organic molecules appear colourless

Answer 45

because the energy difference between

Question 46

why do most organic molecules appear colourless

Answer 46

because the energy difference between HOMO and LUMO is relatively large, resutling in absorption of light from the UV region of the spectrum

Question 47

what are chromophores

Answer 47

a group of atoms within a molecule that is responsible for absorption of light in the visible region of the spectrum

Question 48

when can light be absorbed

Answer 48

when electrons in a chromophore are promoted from the HOMO to the LUMO

Question 49

in which molecules do chromophores exist

Answer 49

those containing a conjugated system

Question 50

what is a conjugated system

Answer 50

a system of adjacent unhybridised p orbitals that overlap side on to form a molecular orbital across a number of carbon atoms

Question 51

what state are electrons in when they are in a conjugated system

Answer 51

delocalised

Question 52

what are examples of molecules with conjugated systems

Answer 52

molecules with alternating single and double bonds aromatic systems

Question 53

what is the relationship between the number of atoms in the conjugated system and the energy gap between HOMO and LUMO

Answer 53

the more atoms in the conjugated system, the smaller the energy gap between HOMO and LUMO.

Question 53

what is the relationship between the number of atoms in the conjugated system and the energy gap between HOMO and LUMO

Answer 53

the more atoms in the conjugated system, the smaller the energy gap between HOMO and LUMO.

Question 54

what happens when a wavelength of light is absorbed in the visible region

Answer 54

the compound will exhibit the complementary colour

Question 55

what happens to the bonds in reactant molecules when an organic reaction takes place

Answer 55

they are broken down and the bonds in the product are made

Question 56

what is bond fission

Answer 56

the process of bond breaking

Question 57

what are the different types of bond fission

Answer 57

homolytic and heterolytic

Question 58

what does homolytic fission result in

Answer 58

the formation of two neutral radical

Question 59

when does homolytic fission occur

Answer 59

when each atom retains one electron from the sigma covalent bond and the bond breaks evenly

Question 60

when does homolytic fission normally occur (in relation to bond types)

Answer 60

when non polar covalent bonds are broken

Question 61

what do reactions involving homolytic fission tend to result in the formation of

Answer 61

a very complex mixture of products, making them unsuitable for organic synthesis

Question 62

what does heterolytic fission result in

Answer 62

the formation of two oppositely charged ions

Question 63

when does heterolytic fission occur

Answer 63

when one atom retains both electrons from the sigma covalent bond and the bond breaks unevenly.

Question 64

when does heterolytic fission usually occur in relation to bonds

Answer 64

when polar covalent bonds are broken

Question 65

why are reactions involving heterolytic fission better suited for organic synthesis

Answer 65

they tend to result in far few products than reactions involving homolytic fission

Question 66

how can the movement of electrons during bond fission and bond making be represented

Answer 66

using curly arrow notation

Question 67

what is a conjugated system

Answer 67

molecules containing delocalised electrons spread over a number of atoms

Question 68

what must be present for the bonds to be conjugated in long carbon chains

Answer 68

alternating single and double bonds