D And F Tb 2

Question 1

÷ (i) The lowest oxide of transition metal is basic, the highest is amphoteric/acidic.

Answer 1

The lowest oxide of transition metal is basic because the metal atom has low oxidation state. This means that it can donate valence electrons which are not involved in bonding to act like a base.
Whereas the highest oxide is acidic due to the highest oxidation state as the valence electrons are involved in bonding and are unavailable. For example, MnO is basic whereas Mn2O7, is acidic.

Question 2

The highest oxidation state is exhibited in oxo-anions of a metal.

Answer 2

Oxometal anions have the highest oxidation state, e.g., Cr in Cr,, has an oxidation state of +6 whereas Mn in Mn, has an oxidation state of +7. This is again due to the combination of the metal with oxygen, which is highly electronegative and oxidising element.

Question 3

What are inner-transition elements? Decide which of the following atomic numbers are the numbers of the inner-transition elements: 29, 59, 74, 95, 102, 104.

Answer 3

The f-block elements, i.e., in which the last electron enters into f-subshell are called inner-transition elements. These include lanthanoids (58-71) and actinoids (90-103). Thus, elements with atomic numbers 59, 95 and 102 are inner-transition elements.

Question 4

The chemistry of the actinoid elements is not so smooth as that of the lanthanoids. Justify this statement by giving some examples from the oxidation state of these elements.

Answer 4

Lanthanoids show a limited number of oxidation state, viz., +2, +3 and +4 (out of which +3 is the most common). This is because of a large energy gap between 4f, 5d and 6s subshells. The dominant oxidation
state of actinoids is also +3 but they show a number of other oxidation states also, e.., uranium (2 = 92)
and plutonium (Z = 94) show +3, +4, +5 and +6, neptunium (Z = 94) shows +3, +4, +5 and +7, etc. This is
due to small energy difference between 5f, 6d and 7s subshells of the actinoids.

Question 5

Comment on the statement that elements of the first transition series possess many properties
different from those of heavier transition elements.

Answer 5

(i) Atomic radii of the heavier transition elements (4d and 5d-series) are larger than those of the corresponding elements of the first transition series though those of 4d and 5d-series are very close to each other.

(ii) Ionisation enthalpies of 5d- series are higher than the corresponding elements of 3d and 4d-series.
(iii) Enthalpies of atomisation of 4d and 5d-series are higher than the corresponding elements of the first series.
(iv) Melting and boiling points of heavier transition elements are greater than those of the first transition
series due to stronger intermetallic bonding.