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(2) Molecular Orbital Theory > Atomic Orbitals > Flashcards

Atomic Orbitals Flashcards

1
Q

What is molecular orbital theory?

A

This involves the formation of molecular orbitals from the combinations of atomic orbitals
Wavefunction are built up to describe the regions of space that the e occupy in the molecule
E can be delocalised across entire molecule rather than localised in bonds

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2
Q

What is a wave function?

A

A function that satisfies a wave equation and describes the properties of a wave

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3
Q

What is a molecular orbital?

A

Molecular orbitals are orbitals that arise from interactions between atomic orbitals
- only if symmetries are compatible
It is single electron wavefunction of a molecule

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4
Q

What is an atomic orbital?

A

Atomic orbital are regions of space around the nucleus of an atom where an electron is likely to be found
It is a single electron wavefunction on an atom

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5
Q

What are the other theory’s to bond formation?

A

Lewis structures- relied on atoms obeying octet rule, no info on electrons, cannot explain many molecules
VESPR- geometries, deduced shape from electrons, difficult for big molecules
Valence BT- QM application of LT, assigns electrons to 2 e bonds- bad for big systems

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6
Q

What are the energetic interactions involved in bond formation?

A

1) repulsive interactions between 2 electrons and 2 nuclei

2) attractive interactions between nucleus and electrons in same atom and nucleus and electron in different atoms

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7
Q

What is a potential energy curve?

A

It describes the approach of two atoms to their equilibrium separation

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8
Q

What is the aim of MO theory?

A

Attempt to obtain wavefunction for the entire molecules
Aim is to calculate the regions in space that an electron might occupy- electrons can be delocalised across the whole molecule

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9
Q

Describe the quantum numbers

A 
n= principle quantum number (energy)
l= angular momentum (shape)
m= magnetic quantum number
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10
Q

What are the quantum numbers associated with an S orbital?

A

l=0
ml= 0

There is 1 orbital per shell

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11
Q

What are the quantum numbers associated with a p orbital?

A

l= 1
ml= +1, 0, +1
There are 3 orbitals in a shell, one along x, one along y and one along z axis

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12
Q

What are the quantum numbers associated with a d orbital?

A

l=2
ml= +2….-2

There are 5 d orbitals per shell

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13
Q

Describe the shape of the d orbitals

A

Name based on which acid emerges from lobe for dyz, dxy, dxz
dx2-y2 the lobes go directly through the axis
dz2 goes directly through 2 axis with e density in a ring towards the centre

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14
Q

What are the quantum numbers associated with an F orbital?

A

l=3
ml= +3….-3
There are 7 f orbitals per shell

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15
Q

Describe the phase of an s orbital

A

S orbitals are spherically symmetrical and so have the same phase over the entire surface
(Constant phase at boundary surface)

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16
Q

Describe the R(r) vs r graph for an s orbital

A

Has electron density near the nucleus and so it doesn’t start at zero, it has no nodes so is a smooth curve

17
Q

Describe the phase of a p orbital

A

P orbitals have one phase in one lobe and a different phase in the other lobe

18
Q

Describe the R(r) vs r graph of a p orbital

A

It has no electron density near the nucleus and so starts at zero with a 1 bump curve

19
Q

What is constructive interference?

A

When the peak of the first wave coincides with peak of a second wave and the amplitudes of the two waves add together

20
Q

What is destructive interference?

A

When the peak of the first wave coincides with the trough of the second wave and the two waves cancel each other out

21
Q

How is the overall wavefunction for a molecule built up?

A

Overall wavefunction can be build from a single electron wavefunction

22
Q

What is the orbital approximation?

A

In an N electron atom, the overall wavefunction can be built up from Nsingle electron wavefunction (same as Nelectron molecule)

23
Q

What is a bonding orbital?

A

A type of MO that if occupied by electrons, stabilised the bond between the two atoms and helps lower the energy of the Molecule relative to the two separated atoms
They have a build up of electron density in the bonding region between the nuclei

24
Q

What does the wavefunction squared tell you?

A

This tells you about the probability of finding an electron at a point in space

25
Q

What is phase?

A

This tells you whether the amplitude of the wavefunction is positive or negative

26
Q

What does an in phase combination of orbitals lead to?

A

Constructive interference which leads to a bonding MO
- larger wavefunction between nuclei
- there is an increase in electron density between the nucleus- forms bond - stabilise the repulsing nuclei
There is extra electrons probability between the nucleus

27
Q

Describe in phase combination in terms of R(r) graphs

A

The two wavefunction add together constructively

Wavefunction squared shows there is extra electron probability between the nuclei

28
Q

What is the mathematical representation of in phase interaction?

A

¥MO= ¥AO + ¥ AO
¥MO2= (¥AO + ¥ AO)2 =
¥AO2 + ¥ AO2 + 2¥AOAO

This shows the extra probability from forming a sigma bond

29
Q

What is an antibonding orbital?

A

A type of MO that d occupied by electrons, weakens the bond between two atoms and helps to raise the energy of the molecule relative to the separated atoms
Orbital has more nodes in bonding region- reduction of e density between the nuclei

30
Q

What is a nodal plane?

A

The wavefunction at any point on the nodal plane is zero which means there is zero electron density at this point

31
Q

What does the out of phase combination of orbitals lead to?

A

Destructive interference which leads to an antibonding MO
- smaller wavefunction between nuclei
- there is an decrease in electron density between the nucleus- forms bond - nothing to stabilise the repulsing nuclei
There is zero electrons probability between the nucleus (nodal plane)

32
Q

Describe the out of phase combination in terms of R(r) vs r graphs

A

The two wavefunction add together destructively
This leads to cancellation of wavefunction between the nuceli
Wavefunction squared shows there is reduced electron density between nuclei, shoes the probability is localised outside of the nucleus

33
Q

What is the mathematical representation of a out of phase combination?

A

¥MO= ¥AO - ¥ AO
¥MO2= (¥AO - ¥ AO)2 =
¥AO2 + ¥ AO2 - 2¥AOAO

This shows the reduction in electron density

(2) Molecular Orbital Theory (5 decks)

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