Vidaara.orgClass 12 · Chemistry
CodeVID-C12-08-T1-01
Assignment — Transition Elements: Trends
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
The d-block elements lie in groups:
- A.1 and 2
- B.3 to 12
- C.13 to 18
- D.1 to 2 and 17
2.
Chromium has the configuration:
- A.$[\text{Ar}]3d^4\,4s^2$
- B.$[\text{Ar}]3d^5\,4s^1$
- C.$[\text{Ar}]3d^6$
- D.$[\text{Ar}]3d^3\,4s^2$
3.
Which is NOT a typical transition element?
- A.Fe
- B.Cr
- C.Zn
- D.Mn
4.
The most common oxidation state of the first half of the 3d series is:
- A.+1
- B.+2
- C.+5
- D.+7
5.
Melting points across a 3d series are highest near:
- A.the start
- B.the middle
- C.the end
- D.they do not vary
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Define a transition element using the IUPAC criterion.
7.
Why does Mn show a dip in melting point within the 3d series?
8.
State why ionisation enthalpies of transition metals rise only gradually.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Explain the variation of atomic radius across the 3d series.
10.
Account for the variable oxidation states of transition metals with an example.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Compare Zn, Cd and Hg with typical transition metals under at least four properties and justify why they are not regarded as typical transition elements.
Answer Key
Section A — Multiple Choice Questions
- (B) 3 to 12
- (B) $[\text{Ar}]3d^5\,4s^1$
- (C) Zn
- (B) +2
- (B) the middle
Section B — Short Answer (2 marks)
- An element with an incompletely filled d subshell in its elemental state or in one of its common oxidation states.
- Its stable half-filled $3d^5$ configuration makes fewer d electrons available for metallic bonding, lowering the melting point.
- Added electrons enter the inner $(n-1)d$ shell, which screens the nucleus and partly offsets the rising nuclear charge.
Section C — Short Answer (3 marks)
- It decreases at the start (rising nuclear charge), stays nearly constant in the middle (d-electron screening balances charge) and rises slightly at the end (electron repulsion in the filling d subshell).
- The $(n-1)d$ and $ns$ electrons have similar energies and can both be lost, e.g. Mn loses 2 to 7 electrons giving +2 to +7.
Section D — Long Answer (5 marks)
- They have $d^{10}$ in atom and common ion, so: (i) colourless ions (no d-d transitions), (ii) low melting points / Hg liquid (no unpaired d electrons for bonding), (iii) poor catalytic activity, (iv) few complexes and almost fixed +2 state. Lacking a partially filled d subshell, they show none of the characteristic transition-metal behaviour.
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