KA1: Molecular orbitals

Question 1

what theory can provide an explanation for bonding in more complex molecules?

Answer 1

molecular orbital theory

Question 2

when do molecular orbitals form?

Answer 2

when atomic orbitals combine

Question 3

the no. of molecular orbitals formed=

Answer 3

the no. of atomic orbitals that combine

Question 4

what does the combination of two atomic orbitals result in?

Answer 4

bonding molecular orbital and an antibonding orbital

Question 5

what does the bonding molecular orbital encompass?

Answer 5

both nuclei

Question 6

what is the basis of bonding between atoms?

Answer 6

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

Question 7

what is the max no. of electrons that each molecular orbital can hold?

Answer 7

2

Question 8

describe the bonding molecular orbital in a non-polar covalent bond

Answer 8

symmetrical about the midpoint between two atoms

Question 9

what do polar covalent bonds result from?

Answer 9

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

Question 10

the atom with the greater value for electronegativity has…

Answer 10

the greater share of bonding electrons

Question 11

what are ionic compounds an extreme case of?

Answer 11

asymmetry

the bonding molecular orbitals almost entirely located around just one atom=resulting in the formation of ions

Question 12

what are sigma (σ) molecular orbitals or sigma bonds?

Answer 12

orbitals bond end-on

Question 13

what are pi (π) molecular orbitals or pi bonds?

Answer 13

orbitals bond side-on

Question 14

what does the electronic configuration of an isolated carbon atom not explain?

Answer 14

the number of bonds formed by carbon atoms in molecules

Question 15

what does hybridisation explain?

Answer 15

the bonding and shape of molecules of carbon

Question 16

what is hybridisation?

Answer 16

the process of mixing atomic orbitals within an atom to generate a set of new atomic orbitals called hybrid orbitals

these hybrid orbitals are degenerate

Question 17

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

Answer 17

four degenerate sp3 hybrid orbitals

Question 18

what arrangement do the four sp3 hydrid orbitals adopt?

Answer 18

tetrahydral

Question 19

what do the sp3 hybrid orbitals form and how to they do this?

Answer 19

-σ bonds

-overlap end-on with other atomic orbitals

Question 20

what can the bonding alkenes be described in terms of?

Answer 20

sp2 hydrisation

Question 21

when are three degenerate sp2 hybrid orbitals formed?

Answer 21

when the 2s orbital and two of the 2p orbitals hybridise

Question 22

what arrangement do the sp2 orbitlas adopt?

Answer 22

trigonal planar

Question 23

how do the hybrid sp2 orbitals overlap to form σ bonds?

Answer 23

end-on

Question 24

what happens to the remaining 2p orbital on each carbon atom on the double bond?

Answer 24

its unhybridised and lie perpendicular to the axis of the σ bond

the unhydridised p orbitals overlap side-on to form π bonds

Question 25

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

Answer 25

sp2 hybridisation

Question 26

describe the structure and bonding of the 6 carbons in benzene

Answer 26

-cyclic structure
-σ bonds between carbons

Question 27

what happens to the unhybridised p orbitals on each carbon atom?

Answer 27

-overlap side-on to form a π molecular system, perpendicular to the plane of the σ bonds

this molecular system extends across all six carbons

the electrons in this system are delocalised

Question 28

what can the bonding in alkynes be described in terms of?

Answer 28

sp hybridisation

Question 29

in alkynes, when are two degenerate hybrid orbitals formed?

Answer 29

2s orbital +one 2p orbital of carbon hybridise

Question 30

in alkynes, what arrangement do the 2s orbital and one 2p orbital adopt?

Answer 30

linear

Question 31

in alkynes, describe the structure and bonding in the 2s and 2p orbital

Answer 31

-hybrid sp orbitals overlap end-on to form σ bonds.

-the remaining two 2p orbitals on each carbon atom lie perpendicular to each oter and to the σ bond

-the unhybridised p orbitals overlap side-on to form two π bonds

Question 32

what theory can be used to explain why organic
molecules are colourless or coloured?

Answer 32

molecular orbital theory

Question 33

describe the order of filling of electrons

Answer 33

electrons fill bonding molecular orbitals, leaving higher energy antibonding orbitas unfilled

Question 34

what is the highest bonding molecular orbital (HOMO)?

Answer 34

the highest occupied molecular orbital containing electrons

Question 35

what is the lowest unoccupied molecular orbital (LUMO)?

Answer 35

the lowest antibonding molecular orbital

Question 36

what causes electrons to be promoted from HOMO to LUMO?

Answer 36

absorption of electromagnetic energy

Question 37

why do most organic molecules appear colourless?

Answer 37

energy difference between HOMO and LUMO is large

results in absorption of light from the ultraviolet region of the spectrum

Question 38

what do some organic molecules contain?

Answer 38

chromophores

Question 39

what is a chromophore?

Answer 39

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

light can be absorbed when electrons in a chromophore are promoted from the HOMO to the LUMO.

Question 40

where do chromophores exist?

Answer 40

in molecules containing a conjugted system

Question 41

what is a conjugated system?

Answer 41

alternating single and double bonds

Question 42

which molecules have conjugated systems

Answer 42

molecules with alternating single and double bonds, and aromatic molecules have conjugated systems

Question 43

describe the relationship between conjugated systems and HUMO/LUMO

Answer 43

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

Question 44

explain the relationship between conjugated systems and HUMO/LUMO

Answer 44

A lower frequency of light (longer wavelength, lower energy) is absorbed by the compound. When the wavelength of light absorbed is in the visible region, the compound will exhibit the complementary colour