3.1 - Molecular orbitals

Question 1

what are formed when atomic orbitals combine

Answer 1

molecular orbitals

Question 2

how many molecular orbitals are formed from two atomic orbitals combining?

Answer 2

2

Question 3

what are the 2 types of molecular orbital formed from the combination of 2 atomic orbitals

Answer 3

a bonding and an antibonding orbital

Question 4

which molecular orbital encompasses both nuclei

Answer 4

the bonding orbital

Question 5

what is the basis of bonding between atoms

Answer 5

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

Question 6

how many electrons can a molecular orbital hold?

Answer 6

2

Question 7

describe how the bonding orbital looks in a non-polar covalent bond

Answer 7

symmetrical about the

midpoint between two atoms

Question 8

describe how the bonding orbital looks in a polar covalent bond

Answer 8

asymmetric about the midpoint between two atoms

Question 9

describe how the bonding orbital looks in an ionic bond

Answer 9

the bonding molecular orbitals being almost entirely located around just one atom

Question 10

what is a sigma bond

Answer 10

a molecular orbital formed by end-on overlap of atomic orbitals along the axis of the covalent bond

Question 11

what is a pi bond

Answer 11

a molecular orbital formed by side-on overlap of parallel atomic orbitals that lie perpendicular to the axis of the covalent bond

Question 12

explain the process of hybridisation

Answer 12

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

Question 13

are hybrid orbitals degenerate

Answer 13

yes

Question 14

what are the 3 hybrid orbitals that carbon can form

Answer 14

(4) sp³, (3) sp² and (2) sp orbitals

Question 15

what spatial arrangement do sp³ orbitals form

Answer 15

tetrahedral

Question 16

what spatial arrangement do sp² orbitals form

Answer 16

trigonal planar

Question 17

what type of bonds do carbon hybrid orbitals form with other atomic orbitals

Answer 17

sigma bonds

Question 18

in a carbon carbon double or triple bonds, what type of bond do the unhybridised orbitals form

Answer 18

pi bonds

Question 19

what is the chemical formula for benzene

Answer 19

C₆H₆

Question 20

how is a a ring of delocalised electrons formed in benzene

Answer 20

the unhybridised p orbitals on each carbon atom overlap side-on forming a pi molecular system, between all six carbon atoms.

Question 21

what is the name for hydrocarbons containing a carbon-carbon triple bond

Answer 21

alkynes

Question 22

what does HOMO stand for

Answer 22

highest occupied molecular orbital

Question 23

what does LUMO stand for

Answer 23

lowest unoccupied molecular orbital

Question 24

is the HOMO a bonding or antibonding orbital

Answer 24

bonding

Question 25

do electrons usually fill bonding, or antibonding orbitals

Answer 25

bonding

Question 26

what causes electrons to be promoted from HOMO to LUMO

Answer 26

absorption of electromagnetic radiation

Question 27

why do most organic molecules appear colourless

Answer 27

the energy difference between HOMO and LUMO is relatively large, causing radiation emitted to be in the UV spectrum

Question 28

what is a chromophore

Answer 28

the region of a molecule which determines its colour

Question 29

chromophores exist in molecules containing what

Answer 29

a conjugated system

Question 30

what is a conjugated system

Answer 30

a system of adjacent unhybridised p orbitals that overlap side-on to form a molecular orbital across a number of carbon atoms. electrons are delocalised.

Question 31

which molecules have a conjugate system

Answer 31

molecules with alternating single and double bonds, and aromatic molecules

Question 32

what decreases the energy gap between HOMO and LUMO

Answer 32

the more atoms in the conjugated system

Question 33

when does a compound appear coloured

Answer 33

when the wavelength of light absorbed is in the visible region (the compound will exhibit the complementary colour)