Interaction of Radiation

Question 1

what happens when radiation interacts with matter?

Answer 1

electromagnetic radiation from the sun reaches the Earth where it interacts with the stratosphere, the UV waves interract with the particles in the air.
- microwaves alter the rotational energy level
- IR alter the vibrational energy level
- Visible/UV alter the electron energy level and can cause photodissociation and ionisation

Question 2

what type of radiation does the earth mainly emit?

Answer 2

Infrared radiation

Question 3

what type of radiation does the sun mainly emit?

Answer 3

Ultraviolet radiation

Question 4

what happens to molecules when they absorb radiation?

Answer 4

molecules change in vibrational energy states, so their bonds vibrate more

Question 5

how can you calculate the values of frequency and energy of electromagnetic radiation?

Answer 5

using E = h x v
E = energy
h = 6.63 x10 - 34 (planks constant)
v = frequency in Hz

Question 6

photodissociation: how to calculate the minimum frequency needed to break a particular covalent bond

Answer 6

1. convert from kJmol-1 to Jmol-1, multiply by 1000
2. convert from ‘per mole’ to ‘per molecule’, divide by avagadro’s number (6.02x1023)
3. convert from energy (in J) to frequency (in Hz) using E = h x v, divide by planks constant
   if they ask for wave length use C = λ v

Question 7

what does it mean when a molecule is quantised?

Answer 7

when electrons in a molecule are in fixed energy levels, they can jump to a higher energy level if absorbing EM radiation

Question 8

what can UV and visible radiation cause electrons to do?

Answer 8

they can promote electrons to higher energy levels sometimes causing bond breaking

Question 9

what are the three types of waves a molecule can absorb?

Answer 9

• microwaves
• IR, infrared
• Visible/UV

Question 10

what can microwaves do if absorbed by a molecule?

Answer 10

microwaves of certain frequencies (between 1x10^-22 and 1x10^-20 J) to alter its rotational energy level

Question 11

what can infrared radiation do if absorbed by a molecule?

Answer 11

infrared of certain frequencies (between 1x10^-20 and 1x10^-19 J) to alter its vibrational energy levels

Question 12

what can visible/UV radiation do if absorbed by a molecule?

Answer 12

Visible/UV of certain specific frequencies (between 1x10^-19 and 1x10^-18 J) to alter the energy level of its electrons

Question 13

what other things can happen to a molecule depending how high the UV is?

Answer 13

• photodissociation when the bond in a molecule breaks
• ionisation where an electron is lost giving a positive ion