Lecture 8

Question 1

Describe paramagnetism

Answer 1

• when there are unpaired electrons, the magnetic moments will align themselves with an externally applied magnetic field
• A normal distribution of spins is random in all directions whereas an alignment in a magnetic field means they all face the same way
• this behaviour is called paramagnetism
• paramagnetic complexes are attracted into
  magnetic fields; the magnitude of the
  attraction depends on the number of unpaired electrons

Question 2

Give the equation for effective magnetic moment, ueff

Answer 2

ueff= √n(n+2)
n= number of unpaired electrons

units; uB or BM, the magnetic moment associated with a single electron in the H atom;

uB= eh/4πm = 9.27 x 10^-2) J T-1
(on data sheet)

Question 3

How can ueff be calculated experimentally?

Answer 3

• When weighed without an applied field and in the presence of a magnetic field, paramagnetic
  substances show: an increase in weight
• From the weight difference, ueff can be calculated and the number of unpaired electrons determined
• can find out whether a complex is high or low spin
• the weighings are carried out in a Gouy balance- paramagnetism pulls sample down and diamagnetism pushes sample up (decrease in weight)

Question 4

What is diamagnetism?

Answer 4

Complexes without unpaired electrons:
external magnetic field still disturbs the
movement of the electrons around the
nuclei (effect is small)

Question 5

How can you calculate magnetic moment and what is it used for?

Answer 5

• determine whether a complex is high or low spin
  1. Use spin only formula to calculate the theortical magnetic moment in uB
  2. Measure the magnetic moment

Question 6

What is ferromagnetism?

Answer 6

• increases degree of magnetism
• the spins spontaneously align in the same direction (below a critical temperature) in the direction of the magnetic field

Question 7

What is the temperature dependence of magnetism?

Answer 7

above the critical temperature, the thermal
energy is high enough to prevent alignment:
χ: magnetic susceptibility, degree of
magnetisation in response to an
applied field
- the curie temperature is where ferromagnetism changes to paramagentism
see page 61 of handout

Question 8

What are the applications of magnetism of TM?

Answer 8

• Metals: magnets e.g. oxides, such as CrO2 recording media: magnetic tape
• Ferrofluids: (made of magnetic nanoparticles suspended in a solvent)
  can be used to seal e.g. rotating shafts