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The D-And-f-Block Elements

Question
CBSEENCH12007293
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(a) Comment on the following tendencies of transition elements of first series:
(i) They exhibit variable oxidation states.
(ii) They easily form alloys.
(iii) They often act as catalyst.
(b) State the different characteristic of actinoids and lanthanoids which places them in f-block elements.
(c) How many unpaired electrons are there in Ni2+(aq)?

Solution

i) The ability of the transition metals to exhibit variable valency is generally attributed to the availability of more electrons in the (n-1)d orbitals which are closer to the outermost ns orbital in energy levels.

ii) An alloy is a blend of metals prepared by mixing the components. Alloys may be homogeneous solid solutions in which the atoms of one metal are distributed randomly among the atoms of the other.

iii) Transition metals acts as catalyst due to the following reasons:

(a) Their partially empty d-orbitals provide surface area for reactant molecules.
(b) They combine with reactant molecules to form transition states and lowers their activation energy.
(c) They show multiple oxidation states and by giving electrons to reactants they form complexes and lower their energies.

b)

Characteristics

Lanthanoids

Actinides

(a) Electronic configuration

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

It may be represented by [Rn]5fx 6dy 7s2,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.


c) Electronic configuration of nicklel is [Ar] 4s2 3d8. In Ni2+ three unpaired electron is present.

Some More Questions From The d-And-f-Block Elements Chapter

How would you account for the irregular variation of ionisation enthalpies (first and second) in the first series of the transition elements?

Why is the highest oxidation state of a metal exhibited in its oxide or fluoride only?

Which is a stronger reducing agent Cr2+ or Fe2+ and why?

Explain why Cu+ ion is not stable in aqueous solutions?

Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

On what ground can you say that scandium (Z = 21) is a transition element but zinc (Z = 30) is not?

The outer electronic configuration of copper is 3d10 4s1, yet it is considered transition element. Why?

Why the melting points of transition elements are high?

Why Zn, Cd and Hg are not regarded as transition elements?

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