Molecular Orbitals

Question 1

What can VSEPR not explain?

Answer 1

The bonding in all compounds.

Question 2

Molecular orbital theory can provide?

Answer 2

An explanation for more complex molecules

Question 3

Molecular orbitals form…

Answer 3

When atomic orbitals combine.

Question 4

The number of molecular orbitals formed is equal to what?

Answer 4

The number of atomic orbitals that combine.

Question 5

The combination of two atomic orbitals results in?

Answer 5

The formation of a bonding molecular orbital and an antibonding orbital.

Question 6

The bonding molecular orbital encompasses?

Answer 6

Both nuclei

Question 7

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

Answer 7

the basis of bonding between atoms.

Question 8

Each molecular orbital can hold a maximum of how many electrons?

Answer 8

Two

Question 9

In a non-polar covalent bond, the bonding molecular orbital is? About what point?

Answer 9

Symmetrical about the midpoint between two atoms.

Question 10

Polar covalent bonds result from?

Answer 10

Bonding molecular orbitals that are asymmetric about the midpoint between two atoms.

Question 11

The atom with the greater value for electronegativity has the…

Answer 11

Greater share of the bonding electrons.

Question 12

Ionic compounds are an extreme case of? Where are bonding molecular orbitals located?

Answer 12

Asymmetry, with the bonding molecular orbitals being almost entirely located around just one atom, resulting in the formation of ions.

Question 13

Molecular orbitals that form by end-on overlap of?

Answer 13

Atomic orbitals along the axis of the covalent bond are called sigma (σ) molecular orbitals or sigma bonds.

Question 14

Molecular orbitals that form by side-on overlap of parallel atomic orbitals that lie perpendicular to the axis of the covalent bond are called?

Answer 14

pi (𝜋) molecular orbitals or pi bonds.

Question 15

The electronic configuration of an isolated carbon atom cannot explain?

Answer 15

The number of bonds formed by carbon atoms in molecules.

Question 16

The bonding and shape of molecules of carbon can be explained by?

Answer 16

Hybridisation.

Question 17

Hybridisation is the process of?

Answer 17

Mixing atomic orbitals within an atom to generate a set of new atomic orbitals called hybrid orbitals. These hybrid orbitals are degenerate.

Question 18

In alkanes, the 2s orbital and the three 2p orbitals of carbon hybridise to? What arrangement do these adopt?

Answer 18

Form four degenerate sp3 hybrid orbitals. These adopt a tetrahedral arrangement.

Question 19

The sp3 hybrid orbitals overlap how? To form?

Answer 19

End-on with other atomic orbitals to form bonds.

Question 20

The bonding in alkenes can be described in terms of?

Answer 20

sp2 hybridisation.

Question 21

The 2s orbital and two of the 2p orbitals hybridise to form? Which adopt what arrangement?

Answer 21

Three degenerate sp2 hybrid orbitals. These adopt a trigonal planar arrangement.

Question 22

The hybrid sp2 orbitals overlap…

Answer 22

end-on to form bonds.

Question 23

The remaining 2p orbital on each carbon atom of the double bond is? How does it lie?

Answer 23

unhybridised and lies perpendicular to the axis of the bond.

Question 24

The unhybridised p orbitals overlap side-on to form?

Answer 24

Bonds

Question 25

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

Answer 25

sp2 hybridisation.

Question 26

The six carbon atoms in benzene are arranged in what sort of structure?

Answer 26

A cyclic structure with bonds between the carbon atoms.

Question 27

The unhybridised p orbitals on each carbon atom overlap side-on to form a… which extends?

Answer 27

molecular system, perpendicular to the plane of the bonds. This molecular system extends across all six carbon atoms. The electrons in this system are delocalised.

Question 28

The bonding in alkynes can be described in terms of? What arrangement do these adopt?

Answer 28

sp hybridisation. The 2s orbital and one 2p orbital of carbon hybridise to form two degenerate hybrid orbitals. These adopt a linear arrangement.

Question 29

The hybrid sp orbitals overlap.. How do the remaining orbitals lie?

Answer 29

end-on to form bonds. The remaining two 2p orbitals on each carbon atom lie perpendicular to each other and to the axis of the bond.

Question 30

The unhybridised p orbitals overlap side-on to form?

Answer 30

Two bonds

Question 31

Molecular orbital theory can be used to explain?

Answer 31

Why organic molecules are colourless or coloured.

Question 32

Electrons fill bonding molecular orbitals, leaving?

Answer 32

Higher energy antibonding orbitals unfilled.

Question 33

The highest bonding molecular orbital containing electrons is called?

Answer 33

the highest occupied molecular orbital (HOMO).

Question 34

The lowest antibonding molecular orbital is called?

Answer 34

the lowest unoccupied molecular orbital (LUMO).

Question 35

Absorption of electromagnetic energy can cause electrons to be?

Answer 35

Promoted from HOMO to LUMO.

Question 36

Most organic molecules appear colourless because? Where is light absorbed?

Answer 36

The energy difference between HOMO and LUMO is relatively large. This results in absorption of light from the ultraviolet region of the spectrum

Question 37

Some organic molecules contain?

Answer 37

Chromophores

Question 38

A chromophore is? What’s it responsible for?

Answer 38

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

Question 39

Light can be absorbed when?

Answer 39

Electrons in a chromophore are promoted from the HOMO to the LUMO.

Question 40

Chromophores exist in molecules containing a…

Answer 40

conjugated system

Question 41

What is a conjugated system?

Answer 41

A system of adjacent unhybridised p orbitals that overlap side-on to form a molecular orbital across a number of carbon atoms. Electrons within this conjugated system are delocalised.

Question 42

Molecules with alternating single and double bonds, and aromatic molecules have?

Answer 42

conjugated systems.

Question 43

The more atoms in the conjugated system the smaller the? What frequency of light is absorbed by the compound?

Answer 43

Energy gap between HOMO and LUMO. A lower frequency of light (longer wavelength, lower energy) is absorbed by the compound.

Question 44

When the wavelength of light absorbed is in the visible region, the compound will exhibit?

Answer 44

The complementary colour.

Question 45

Compounds highlighting the effect of increasing the length of…. Give an example?

Answer 45

The conjugated system on the colour can be compared. For example, vitamin A (yellow) can be compared with -carotene (orange).

Question 46

Ninhydrin reacts with? Forming? What is this used in the detection of?

Answer 46

Amino acids and forms a highly conjugated product that absorbs light in the visible region, and an intense purple colour (λmax 750 nm) is observed. This is used in the detection of amino acids both as a locating agent in chromatography and in detecting latent fingerprints in crime scenes.