F-block Chemistry

Question 1

What are the exceptions to the general configuration of lanthanides?

Answer 1

Ce, Gd, Lu

Question 2

When gradually filling the valence orbitals which is the first orbital occupied and why?

Answer 2

• the first orbital occupied is the 6s because 6s orbitals are non-nodal at the nucleus

Question 3

What happens as Z increases to the lanthanides and consequently what electrons are lost first when cations are formed

Answer 3

• As Z increases the radial distribution functions for the orbitals contract slightly but 4f contracts faster
• the 4f orbitals therefore become much lower in energy and the 6s is highest in energy
• so in the formation of cations 6s electrons are lost first
• followed by one 4f electron

Question 4

Why can lanthanides only lose one 4f electron

Answer 4

• as the lanthanide atom is progressively ionised positive charge builds up on the ion and all the RDFs contract
• but the relatively large stabilisation experienced by the 4f orbitals is such that after losing one 4f electron
• the 4f orbitals become so stabilised that the fourth IE requires too much energy

Question 5

Why are the 6s electrons lost first in lanthanides

Answer 5

• they are on average further from the nucleus
• and are shielded by other electrons
• loss of 6s electrons is then compensated for by the formation of chemical bonds