145.

Compare the chemistry of actinides with that of the lanthanoids with special reference to:
(i) electronic configuration, (ii) atomic and ionic sizes, (iii) oxidation state (iv) chemical reactivity.

Characteristics

Lanthanoids

Actinides

(a) Electronic configuration

It may be represented by [Xe]4f^x 5d^y 6s², where x varies from 0 to 14 and y = 0 or 1.

It may be represented by [Rn]5f^x 6d^y 7s^2,where x varies from 0 to 14 and y = 0 or 1.

(b)    Oxidation state

Show +3 oxidation state only except in few cases where it is +2 or +4. They never show more than +4 state.

Show higher oxidation states such as +4, +5, +6, +7 also in addition to +3.

(c) atomic and ionic sizes

The ionic radii of M³⁺ ions in lanthanoids series show a regular decrease in size of ions with increase in atomic number. This decrease is known as lanthanoid contraction.

There is a greater and gradual decrease in the size of atoms or M³⁺ ions across the series. This greater decrease is known as actinoid contraction.

(d)    Chemical reactivity

These are less reactive metals and form oxides, sulphides, nitrides, hydroxides and halides etc. These also form H₂ with acids. They show a lesser tendency for complex formation

These are highly reactive metals especially when are in finely divided state. They form a mixture of oxide and hydride by action of boiling water. They combine with non-metals even at moderate temperature. They show a greater tendency for complex formation.