Compare
the chemistry of actinoids with that of the lanthanoids with special
reference to:
(i)
electronic configuration
(iii) oxidation
state
(ii)
atomic and ionic sizes and
(iv) chemical
reactivity.
Compare the chemistry of actinoids with that of the lanthanoids with special reference to:
(i) electronic configuration (iii) oxidation state
(ii) atomic and ionic sizes and (iv) chemical reactivity.
(i) Electronic
configuration
The
general electronic configuration for lanthanoids
is [Xe]54
4f0-14
5d0-1
6s2
and that for actinoids is [Rn]86
5f1-14
6d0-1
7s2.
Unlike 4f
orbitals, 5f orbitals
are not deeply buried and participate in bonding to a greater extent.
(ii) Oxidation
states
The
principal oxidation state of lanthanoids is (+3). However, sometimes
we also encounter oxidation states of + 2 and + 4. This
is because of extra stability of fully-filled and half-filled
orbitals. Actinoids exhibit a greater range of oxidation states. This
is because the 5f,
6d, and 7s
levels are of comparable energies. Again, (+3) is the principal
oxidation state for actinoids. Actinoids such as lanthanoids have
more compounds in +3 state than in +4 state.
(iii) Atomic
and lonic sizes
Similar
to lanthanoids, actinoids also exhibit
actinoid contraction (overall decrease in atomic and ionic radii).
The contraction is greater due to the poor shielding effect of 5f
orbitals.
Chemical
reactivity
In
the lanthanide series, the earlier members of the series are more
reactive. They have reactivity that is
comparable to Ca. With an increase in the atomic number, the
lanthanides start behaving similar to Al. Actinoids, on the other
hand, are highly reactive metals, especially when they are finely
divided. When they are added to boiling water, they give a mixture of
oxide and hydride. Actinoids combine with most of the non-metals at
moderate temperatures. Alkalies have no action on these actinoids. In
case of acids, they are slightly affected by nitric acid (because of
the formation of a protective oxide layer).
(i) Electronic configuration
The general electronic configuration for lanthanoids is [Xe]54 4f0-14 5d0-1 6s2 and that for actinoids is [Rn]86 5f1-14 6d0-1 7s2. Unlike 4f orbitals, 5f orbitals are not deeply buried and participate in bonding to a greater extent.
(ii) Oxidation states
The principal oxidation state of lanthanoids is (+3). However, sometimes we also encounter oxidation states of + 2 and + 4. This is because of extra stability of fully-filled and half-filled orbitals. Actinoids exhibit a greater range of oxidation states. This is because the 5f, 6d, and 7s levels are of comparable energies. Again, (+3) is the principal oxidation state for actinoids. Actinoids such as lanthanoids have more compounds in +3 state than in +4 state.
(iii) Atomic and lonic sizes
Similar to lanthanoids, actinoids also exhibit actinoid contraction (overall decrease in atomic and ionic radii). The contraction is greater due to the poor shielding effect of 5f orbitals.
Chemical reactivity
In the lanthanide series, the earlier members of the series are more reactive. They have reactivity that is comparable to Ca. With an increase in the atomic number, the lanthanides start behaving similar to Al. Actinoids, on the other hand, are highly reactive metals, especially when they are finely divided. When they are added to boiling water, they give a mixture of oxide and hydride. Actinoids combine with most of the non-metals at moderate temperatures. Alkalies have no action on these actinoids. In case of acids, they are slightly affected by nitric acid (because of the formation of a protective oxide layer).
