Explain giving reason:
() Transition metals and many of their compounds
show paramagnetic behaviour. JCBSE Learning
Framework, CBSE 2022|
(i) The enthalpies of atomisation of the transition
metals are high. [CBSE Learning Framework, CBSE
2022, 20(C) for Blind; Chennai 2019; Delhi 2017(C)]
(üi) The transition metals generally form coloured
compounds. (CBSE Learning Framework, CBSE
2023,22, 20(C) for Blind; KVS; Delhi 2019, 12; DoE]
(iv) Transition metals and their many compounds
act as good catalyst. |CBSE Learning Framework
2023, 22, 20(C) for Blind; DoE; Pre-Board 20
KVS; Delhi 2019,2017(C))
Ans. () lIt is due to the presence ofunpaired electrons due
to which they are attracted by magnetic field and
showparamagnetism.
(ii) Itis due to strong metallic bonding and additional
covalent bonding due to presence of unpaired
electrons in d-orbitals due to which they have high
lattice energy and consequently, high enthalpy of
atomisation.
(iii) It is due to the presence of unpaired electrons,
due to which they undergo d-d transitions by
absorbing light from visible region and radiate
complementary colour.
(iv) It is due to variable oxidation states. They have
large surface area and can form intermediate with
reactants which readily change into products.
Ans.
(b) Ct(following
)+ ion?
c) Ti(aMagnetic
Ni
=
+2 has moment
2
unpaired
=2 of
2.83
X4
lectrons.
Mn?+(a) Ni(b?)t BM
=
/8 is
given
2.83
by
BM which
of
the
Account for the following.
() Transition metals form large number of complex
compounds.
(ii) Copper () compounds are white whereas Copper
() compounds are coloured. |CBSE 2020|
Ans. () It is due to small size of cations, high charge and
availability of vacant d-orbitals of suitable energy.
(ii) Cu'(3d'") compounds are white because of
absence of unpaired electrons while Cu*(3d')
compounds are coloured due to unpaired e /shows
d-d transition. [1]
|CBSE Marking Scheme]
Although Zr belongs to 4d and Hf belongs to 5d
transitionseries but it isquite difficult to separate
them. Why? |CBSE 2022|
It is due to almost same size (Zr= 160 pm, Hf= 159 pm)
which is due to lanthanoid contraction.
Example Magnetic Moment (BM)
K,[Mn(CN)al 2.2 [CBSE 2020]
[Fe(H,0),1* 5.3
K,[MnCI, 5.9
Mn² has 4s° 3d; u = /n(n+2) = /1 x3 = 1.732
Transition metals form alloys because they have
(a) same atomic number
(b) same electronic configuration
c) nearly same atomic size
(d) vacant d-orbitals
Assign suitable reasons for the following:
(a) In the 3d series from Sc (Z = 21l) to Zn (Z=30),
the enthalpyof atomization of Zn is the lowest.
(6) The Mn compounds are more stable than Fe*
towards oxidation to their +3 state. |CBSE 2022]
(c) Se is colourless in aqueous solution, whereas T
is coloured. |CBSE 2023, 22, 22(C), 20, 18; KVS]
Ans. (a) Zinc does not have unpaired electrons and larger in
size,therefore, has weak metallic bonds. That is why
it has least enthalpy of atomisation.
(b) Mn* has 3d° (stable electronic configuration),
therefore, it does not get oxidised to Mn, whereas
Fe has 3d which readily changes to Fe (3d)
which has stable electronic configuration.
(c) Se*is colourless as it does not have unpaired electron
and cannot undergo d-d transition, whereas Ti is
coloured due to presence of unpaired electrons, and
undergoes d-d transition by absorbing light from
visible region and radiate complementary colour.
