Molecular Orbitals Flashcards

1
Q

What does covalent bonding between atoms involve?

A

the overlap of atomic orbitals (s,p orbtials) to form molecular orbitals (π σ)

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2
Q

How are molecular orbitals formed?

A

By the linear combination of atomic orbitals

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3
Q

What maximum number of electrons can each molecular orbital hold?

A

2

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4
Q

What are the two types of molecular orbitals?

A

bonding and antibonding

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5
Q

What are molecular orbitals formed by the overlap of s orbitals denoted with?

A

sigma (σ)

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6
Q

Why is it called a bonding molecular orbital?

A

the electrons in this orbital spend most of their time in the region directly between the two nuclei

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7
Q

Why is it called a σ molecular orbital?

A

it looks like an s orbital when viewed along the bond axis

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8
Q

How is a bonding molecular orbital made?

A

by adding the mathematical functions for the atomic orbitals that come together to form the molecule

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9
Q

How is an antibonding molecular orbital made?

A

by subtracting one functiokn from the other

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10
Q

Why is it called an antibonding molecular orbital?

A

the electrons spend most of their time away from the region between the two nuceli.

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11
Q

What is an antibinding molecular orbital denoted with?

A

σ*

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12
Q

How are electrons added to molecular orbitals?

A

one at a time, starting with the lowest energy molecular orbital

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13
Q

In terms of a H2 molecule and its molecular orbital diagram, talk about its stability.

A

The diagram suggests that the energy of a H2 molecule is lower than that of the H atoms. As a result, the H2 molecule is more stable than a pair of isolated H atoms.

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14
Q

Give the 3 possible orbital combinations that form σ bonds.

A
  1. s orbital + s orbital
  2. s orbital + p orbital
  3. p-orbital + p orbital (‘head-on’ overlap)
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15
Q

How are π bonds formed?

A

by the lateral overlap of p orbitals

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16
Q

Why are they called π molecular orbitals?

A

They look like p orbitals when viewed along the line of the bond

17
Q

When carbon forms bonds, what happens to one of the 2s electrons?

A

it is promoted to a higher energy 2p orbital

18
Q

When carbon forms bonds, what happens to the 2s and three 2p orbitals?

A

they combine to make 4 equivalent orbitals called sp3 hybrid orbitals

19
Q

How many electrons does each sp3 hybrid orbital hold?

A

1

20
Q

What arrangement do the 4 sp3 hybrid orbitals take up?

A

tetrahedral

21
Q

For methane, what does each sp3 hybrid orbital on carbon do?

A

overlap with a 1s orbital of H to give 4 equivelant sigma (σ) bonds

22
Q

What are all 7 of the bonds in ethane?

A

σ bonds

23
Q

What are σ bonds found in?

A

all saturated molecules

24
Q

What is sp3 hybridisation found in?

A

all saturated molecules

25
Q

For bonding in alkenes, what kind of hybridisation occurs?

A

sp2 hybridisation

26
Q

Describe sp2 hybridisation.

A

It is the combination of the 2s orbital with 2 2p orbitals giving three equivelent sp2 hybrid orbitals

27
Q

What arrangement do the 3 sp2 hybrid orbitals adopt?

A

trigonal planar

28
Q

How does the unhybridised p-orbital sit?

A

sits at 90’ to the planar structure

29
Q

Describe what happens to 2 sp2 hybrid orbitals in ethene?

A

they overlap to form a σ bond

30
Q

Describe what happens to the p orbitals on adjacent C atoms in ethene?

A

they overlap to form a π bond

31
Q

In ethene, what does the double bond consist of?

A

a σ and a π bond

32
Q

What do all double bonded C atoms show?

A

sp2 hybridisation

33
Q

Why are π bonds weaker than σ bonds?

A

the electrons in the bond are not localised between the nuclei

34
Q

What will the shape of the molecular orbital formed from overlapping atomic orbitals govern?

A

the type of intermolecular bonding that is observed

35
Q

Non-polar/ pure covalent bonds are formed between two atoms of the same element, or two atomd with a very low difference in electronegativities. Describe what effect this has on the molecular orbitals.

A

The molecular orbital formed from overlapping atomic orbitals is symmetrical around a mid-point where the bonding electrons are most likely to be found

36
Q

For when there is a large difference in electronegativities, describe the shape of the bonding molecular orbital.

A

asymmetrical