molecular orbitals

Question 1

what can molecular orbital provide an explanation for

Answer 1

VSEPR cannot explain the bonding in all compounds. Molecular orbital theory can provide an explanation for more complex molecules.

Question 2

when do molecular orbitals form

Answer 2

Molecular orbitals form when atomic orbitals combine.

Question 3

what is the number of molecular orbitals formed equal to

Answer 3

The number of molecular orbitals formed is equal to the number of atomic orbitals that combine.

Question 4

what is result of the combination of two
atomic orbitals

Answer 4

The combination of two
atomic orbitals results in the formation of a bonding molecular orbital and an antibonding orbital.

Question 5

what does the bonding molecular orbital encompass

Answer 5

The bonding molecular orbital encompasses 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 is the basis of bonding between atoms.

Question 7

In a non-polar covalent bond what is the bonding molecular orbital

Answer 7

In a non-polar covalent bond, the bonding molecular orbital is symmetrical about the
midpoint between two atoms.

Question 8

what do Polar covalent bonds result in

Answer 8

Polar covalent bonds result from bonding molecular orbitals that are asymmetric about the midpoint between two atoms.

Question 9

The atom with the greater
value for electronegativity has what?

Answer 9

The atom with the greater
value for electronegativity has the greater share of the bonding electrons.

Question 10

Ionic compounds
are an extreme case of what?

Answer 10

Ionic compounds
are an extreme case of asymmetry, with the bonding molecular orbitals being almost entirely located around just one atom, resulting in the formation of ions.

Question 11

what are sigma molecular orbitals/ sigma bonds

Answer 11

Molecular orbitals that form by end-on overlap of atomic orbitals along the axis of the
covalent bond are called sigma (σ ) molecular orbitals or sigma bonds.

Question 12

what are pi bonds

Answer 12

Molecular orbitals that form by side-on overlap of parallel atomic orbitals that lie perpendicular to the axis of the covalent bond are called pi (π ) molecular orbitals or
pi bonds.

Question 13

what can the electronic configuration of an isolated carbon atom not explain

Answer 13

The electronic configuration of an isolated carbon atom cannot explain the number of bonds formed by carbon atoms in molecules

Question 14

how is the bonding and shape of molecules of carbon explained

Answer 14

The bonding and shape of molecules of carbon can be explained by hybridisation.

Question 15

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

Answer 15

In alkanes, the 2s orbital and the three 2p orbitals of carbon hybridise to form four degenerate sp3 hybrid orbitals. These adopt a tetrahedral arrangement. The sp3 hybrid orbitals overlap end-on with other atomic orbitals to form σ bonds.

Question 16

what can the bondiing in alkenes be described in terms of

Answer 16

The bonding in alkenes can be described in terms of sp2 hybridisation. The 2s orbital and two of the 2p orbitals hybridise to form three degenerate sp2 hybrid orbitals. These adopt a
trigonal planar arrangement.

Question 17

The hybrid sp2 orbitals overlap end-on to form σ bonds. what do the remaining 2p orbitals

Answer 17

The hybrid sp2 orbitals overlap end-on to form σ bonds. The remaining 2p orbital on each carbon atom of the double bond is unhybridised and lies
perpendicular to the axis of the σ bond. The unhybridised p orbitals overlap side-on to form π bonds.

Question 18

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

Answer 18

The bonding in benzene and other aromatic systems can be described in terms of sp2
hybridisation.

Question 19

how are the 6 carbon atoms in benzene arranged

Answer 19

The six carbon atoms in benzene are arranged in a cyclic structure with σ bonds between the carbon atoms. The unhybridised p orbitals on each carbon atom overlap side-on to form a π molecular system, perpendicular to the plane of the σ bonds. This π molecular system extends across all six carbon atoms. The electrons in this
system are delocalised.

Question 20

how can the bonding in alkyenes be described in terms of

Answer 20

The bonding in alkynes can be described in terms of sp hybridisation. The 2s orbital and one 2p orbital of carbon hybridise to form two degenerate hybrid orbitals

Answer 21

These adopt a linear arrangement. The hybrid sp orbitals overlap end-on to form σ bonds. The remaining two 2p orbitals on each carbon atom lie perpendicular to each other and to the axis of the σ bond. The unhybridised p orbitals overlap side-on to form two π bonds.

Question 22

what can molecular orbital theory be used to explain

Answer 22

Molecular orbital theory can be used to explain why organic molecules are colourless or coloured.

Question 23

what leaves antibonding orbitals unfilled

Answer 23

Electrons fill bonding molecular orbitals, leaving higher energy antibonding orbitals unfilled.

Question 24

what is homo and what is lumo

Answer 24

The highest bonding molecular orbital containing electrons is called the highest occupied molecular orbital (HOMO). The lowest antibonding molecular orbital is called the lowest unoccupied molecular orbital (LUMO).

Question 25

what causes electrons to be promoted from homo to lumo

Answer 25

Absorption of electromagnetic energy can cause electrons to be promoted from HOMO to
LUMO.

Question 26

why do most organic molecules appear colourless

Answer 26

Most organic molecules appear colourless because the energy difference between HOMO and LUMO is relatively large. This results in absorption of light from the ultraviolet region of the spectrum.

Question 27

what is a chromophore

Answer 27

Some organic molecules contain chromophores. A chromophore is a group of atoms within a molecule that is responsible for absorption of light in the visible region of the spectrum

Question 28

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

Answer 28

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

Question 29

where do chromophores exist

Answer 29

Chromophores exist in molecules containing a conjugated system — a system of adjacent unhybridised p orbitals that overlap side-on to form a molecular orbital across a number of carbon atoms

Question 30

Chromophores exist in molecules containing a conjugated system what are electrons within this system

Answer 30

Electrons within this conjugated system are delocalised. Molecules with alternating single and double bonds, and aromatic molecules have conjugated systems.

Question 31

The more atoms in the conjugated system the smaller the what?

Answer 31

The more atoms in the conjugated system the smaller the energy gap between HOMO and
LUMO. A lower frequency of light (longer wavelength, lower energy) is absorbed by the compound.

Question 32

When the wavelength of light absorbed is in the visible region what will happen

Answer 32

When the wavelength of light absorbed is in the visible region, the compound will exhibit the complementary colour.

Question 33

what is hybridisation

Answer 33

Hybridisation is 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