Unit 8

Question 1

What is the frequency and wavelength of low energy? eg radio waves

Answer 1

Low frequency high wavelength

Question 2

What is the frequency and wavelength of high energy? eg gamma waves

Answer 2

High frequency low wavelength

Question 3

What energy change and part of the spectrum does electronic spectroscopy occur?

Answer 3

It shows electron movement between orbitals and takes place in the visible, ultra violet and X-ray region

Question 4

What energy change and part of the spectrum does infrared/vibrational spectroscopy occur?

Answer 4

Vibrational changes takes place in the infrared spectrum

Question 5

What energy change and part of the spectrum does rotational spectroscopy occur?

Answer 5

Rotational changes in microwave region

Question 6

Equation for speed?

Answer 6

speed= Frequency X wavelength

Question 7

Equation for energy?

Answer 7

Energy= Frequency X Plancks

Question 8

Equation for energy using wavelength

Answer 8

Energy= Plancks X speed of light/ wavelength

Question 9

What is an electromagnetic wave made out of?

Answer 9

A magnetic field and an electric field at 90 degree angles to each other

Question 10

How does the electric field of a electromagnetic wave affect electrons?

Answer 10

if it matches the energy difference between energy levels it can give the electron kinetic energy to promote the electron (dE=hf)

Question 11

what path does electric field make electrons take?

Answer 11

it makes electrons oscillate and go from positive to negative of the field.

Question 12

What transitions aren’t allowed?

Answer 12

s-s s-d p-p d-d

Question 13

in visible light spectroscopy what causes the colours we see?

Answer 13

Some of the light is absorbed and used in the molecule for vibrations, the light that isn’t absorbed passes through and is visible. If none of the light is absorbed it will just pass through as white light

Question 14

why is copper nitrate blue in water?

Answer 14

Because it forms a complex which will absorb the red parts of light and the blue part will be transmitted which we can see

Question 15

What happens that allows D-d transitions?

Answer 15

The vibrations can split and distort the orbitals symmetry and allow transitions, this is why many transition metal complexes are coloured.

Question 16

What happens when you attach ligands

Answer 16

The electric fields can cause repulsions in the d orbitals and cause them to split into different energy levels

Question 17

Why can’t d-d transitions happen if they have 10 electrons?

Answer 17

All orbitals are filled so there is no empty higher orbital for them to move into

Question 18

Why do d orbitals with 10 electrons in not have a colour?

Answer 18

Because they are fully filled the electrons cant be promoted, therefore they are not absorbing the energy so it just gets released

Question 19

Why do Alkenes and aromatic compounds absorb in the UV spectrum?

Answer 19

Double bonds contain pi electrons which can use energy from the uv region to promote from bonding orbitals to antibonding

Question 20

What region of the magnetic spectrum does electronic spectroscopy take place in/

Answer 20

ultra violet, visible and x-rays

Question 21

What region of the magnetic spectrum does Vibrational spectroscopy take place in?

Answer 21

Infra-red

Question 22

What do multiple conjugated bonds give rise to?

Answer 22

Electron delocalisation

Question 23

What do conjugated bonds do?

Answer 23

Give rise to electron delocalisation, this means electrons require lower energy for bonding to antibonding orbitals

Question 24

What energies do bonding and anti bonding orbitals have compared to the atomic orbitals that made them?

Answer 24

Bonding orbitals have a lower energy than the ones that made them
Anti bonding a higher energy

Question 25

When electrons relax to ground state what is the excess energy used for?

Answer 25

It can be used to increase vibrations in the molecule

Question 26

Why would an absorption band occur in the visible region?

Answer 26

If it has conjugated bonds which give rise to electron delocalisation it wont need as much energy for pi to pi* transitions

Question 27

What allows d-d orbital transition?

Answer 27

Vibrations which cause orbital mixing and distortion which breaks the symmetry

Question 28

can molecules that are colourless still absorb in the uv region?

Answer 28

yes

Question 29

Why is an antibonding orbital not as stable as a bonding?

Answer 29

Bonding orbitals have attractions between the nuclei and electrons in antibonding there are only repulsions

Question 30

What is a conjugated bond?

Answer 30

When multiple p orbitals overlap leading to electron delocalisation.

Question 31

How can you recognise conjugated bonds?

Answer 31

If the bond is shown to be alternating

Question 32

How is a sigma bond formed?

Answer 32

end to end overlap of atomic orbitals