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AH Chemistry > 3.1 - Molecular orbitals > Flashcards

3.1 - Molecular orbitals Flashcards

1
Q

what are formed when atomic orbitals combine

A

molecular orbitals

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2
Q

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

A

2

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3
Q

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

A

a bonding and an antibonding orbital

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4
Q

which molecular orbital encompasses both nuclei

A

the bonding orbital

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5
Q

what is the basis of bonding between atoms

A

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

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6
Q

how many electrons can a molecular orbital hold?

A

2

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7
Q

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

A

symmetrical about the

midpoint between two atoms

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8
Q

describe how the bonding orbital looks in a polar covalent bond

A

asymmetric about the midpoint between two atoms

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9
Q

describe how the bonding orbital looks in an ionic bond

A

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

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10
Q

what is a sigma bond

A

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

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11
Q

what is a pi bond

A

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

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12
Q

explain the process of hybridisation

A

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

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13
Q

are hybrid orbitals degenerate

A

yes

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14
Q

what are the 3 hybrid orbitals that carbon can form

A

(4) sp³, (3) sp² and (2) sp orbitals

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15
Q

what spatial arrangement do sp³ orbitals form

A

tetrahedral

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16
Q

what spatial arrangement do sp² orbitals form

A

trigonal planar

17
Q

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

A

sigma bonds

18
Q

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

A

pi bonds

19
Q

what is the chemical formula for benzene

A

C₆H₆

20
Q

how is a a ring of delocalised electrons formed in benzene

A

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

21
Q

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

A

alkynes

22
Q

what does HOMO stand for

A

highest occupied molecular orbital

23
Q

what does LUMO stand for

A

lowest unoccupied molecular orbital

24
Q

is the HOMO a bonding or antibonding orbital

A

bonding

25
Q

do electrons usually fill bonding, or antibonding orbitals

A

bonding

26
Q

what causes electrons to be promoted from HOMO to LUMO

A

absorption of electromagnetic radiation

27
Q

why do most organic molecules appear colourless

A

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

28
Q

what is a chromophore

A

the region of a molecule which determines its colour

29
Q

chromophores exist in molecules containing what

A

a conjugated system

30
Q

what is a conjugated system

A

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.

31
Q

which molecules have a conjugate system

A

molecules with alternating single and double bonds, and aromatic molecules

32
Q

what decreases the energy gap between HOMO and LUMO

A

the more atoms in the conjugated system

33
Q

when does a compound appear coloured

A

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

AH Chemistry (10 decks)

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