d-BLOCK ELEMENTS No. of lectures – 12 Term - 1

smitaasthana@yahoo.com Paper 2, Unit 1, Chapter 1
d-BLOCK ELEMENTS No. of lectures – 12 Term - 1 Paper 2, Unit 1, Chapter 1

INTRODUCTION OF D-BLOCK ELEMENTS
Paper 2, Unit 1, Chapter 1

Periodic Table d block transition elements f block transition elements Paper 2, Unit 1, Chapter 1

d-Block Transition Elements
Sc Ti V Cr Mn Fe Co Ni Cu Zn Y Zr Nb Mo Tc Ru Rh Pd Ag Cd La Hf Ta W Re Os Ir Pt Au Hg IIIB IVB VB VIB VIIB IB IIB VIIIB Most have partially occupied d sub-shells in common oxidation states Paper 2, Unit 1, Chapter 1

Why are they called d-block elements?
Their last electron enters the d-orbital. Paper 2, Unit 1, Chapter 1

Most d-block elements are also called transition metals. This is because they exhibit characteristics that ranges from s -block to p – block. Zinc group and Scandium group are NOT considered as transition metals, are called Non-typical Transition elements. Paper 2, Unit 1, Chapter 1

What is a transition metal?
For this reason, a transition metal is defined as being an element which forms at least one ion with a partially filled d orbital(s). Paper 2, Unit 1, Chapter 1

The d block: The d block consists of three horizontal series in periods 4, 5 & 6 10 elements in each series Chemistry is “different” from other elements Differences within a group in the d block are less sharp than in s & p block Similarities across a period are greater Paper 2, Unit 1, Chapter 1

Electronic Arrangement
Element Z 3d 4s Sc 21 [Ar]   Ti 22 V 23 Cr 24 Mn 25 Fe 26 Co 27 Ni 28 Cu 29 Zn 30 Paper 2, Unit 1, Chapter 1

Electronic Configuration
Across the 1st row of the d block (Sc to Zn) each element has 1 more electron and 1 more proton Each “additional” electron enters the 3d sub-shell The core configuration for all the 1st series of transition elements is that of Ar 1s22s22p63s23p6 Paper 2, Unit 1, Chapter 1

Chromium and Copper At Cr Orbital energies such that putting one e- into each 3d and 4s orbital gives lower energy than having 2 e- in the 4s orbital At Cu Putting 2 e- into the 4s orbital would give a higher energy than filling the 3d orbitals Paper 2, Unit 1, Chapter 1

Trends in properties Atomic and Ionic radii Decreases across the series as the atomic no. Increases, due increase in nuclear charge. From Sc to Cr - regular expected decrease Increased nuclear attraction b) From Cr to Ni - almost same size nuclear attraction = inter electronic repulsion c) Ni to Zn – Marginal increase nuclear attraction < inter electronic repulsion Paper 2, Unit 1, Chapter 1

2. Ionization Potential Paper 2, Unit 1, Chapter 1

3. Variable Oxidation States
D-block elements exhibit variable oxidation states. This means that they can form two or more different types of cations. Examples: Iron can form both Fe²⁺ and Fe ³⁺ Manganese can Mn²⁺, Mn³⁺, Mn⁴⁺, Mn⁶⁺ and Mn⁷⁺ Paper 2, Unit 1, Chapter 1

Oxidation States of TM’s
Sc Ti V Cr Mn Fe Co Ni Cu Zn +1 +2 +3 +4 +5 +6 +7 Paper 2, Unit 1, Chapter 1

1. No of OS’s shown by an element increases from Sc to Mn In each of these elements highest OS is equal to no. of 3d and 4s e- After Mn decrease in no. of OS’s shown by an element Highest OS shown becomes lower and less stable Seems increasing nuclear charge binds 3d e- more strongly, hence harder to remove Paper 2, Unit 1, Chapter 1

Stability of OS’s General trends Higher OS’s become less stable relative to lower ones on moving from left to right across the series Compounds containing TM’s in high OS’s tend to be oxidising agents e.g MnO4- Compounds with TM’s in low OS’s are often reducing agents e.g V2+ & Fe2+ Paper 2, Unit 1, Chapter 1

In the following table Most important OS’s in boxes OS = +1 only important for Cu OS = +2, where 4s e- lost shown by all except for Sc and Ti OS = +3, shown by all except Zn Paper 2, Unit 1, Chapter 1

Nature of bonds – Ionic and covalent Lower OS’s found in ionic compounds E.g. compounds containing Cr3+, Mn2+, Fe3+, Cu2+ ions TM’s in higher OS’s usually covalently bound to electronegative element such as O or F E.g VO3-, vanadate(V) ion; MnO4-, manganate(VII) ion Simple ions with high OS’s such as V5+ & Mn7+ are not formed Paper 2, Unit 1, Chapter 1

Oxidising and reducing nature
lower oxidation states are highly reducing E.g. V2+(aq) & Cr2+(aq) strong reducing agents higher oxidation states are oxidising in nature E.g. Co3+ is a strong oxidising agent, KMnO4 - OS +7, K 2Cr2 O 7 - OS +6 are oxidising agents Acidic and basic nature Higher oxidation states are acidic in nature Lower oxidation states become increasingly basic via amphoteric nature H2 CrO4 is strong acid – Cr OS +6 Mn 2 O3– basic (+3), MnO 2– amphoteric(+4), KMnO4 – acidic(+7) Paper 2, Unit 1, Chapter 1

Formation of coloured ions The compounds of the d-block metal ions are usually colored, except, those of d0 and d10 metal ions. The colors are due to: Electronic transitions of d-electrons within the d sub-shell. These are known as d→d transitions. When light passes through these compounds, electrons from a lower energy d-orbital absorb a photon of energy and are promoted to higher energy d-orbitals. The energy absorbed is equivalent to the energy difference between the two sets of orbitals. Electron while returning from the excited state gives away the energy which falls in visible range of spectrum and the substance appears coloured. Since light of a certain frequency is absorbed, the light that comes out looks coloured because it lacks some colour. The colour of the compound is the complementary of the one that was absorbed Paper 2, Unit 1, Chapter 1

Ferromagnetism and Paramagnetism
EOS Paper 2, Unit 1, Chapter 1

Magnetic behaviour Electron is a micromagnet, moves On its axis – Spin moment In the orbitals – Orbital moment Total magnetic moment = Spin moment + Orbital moment µ(S + L) = √4S (S+1) + L( L + 1) Orbital moment is negligible, µ eff. = √ n(n+2) B.M. Paper 2, Unit 1, Chapter 1

Titanium Zirconium Hafnium Rutherfordium [Ar] 4s23d2 [Kr] 5s2 4d2 [Xe] 6s2 4f14 5d2 [Rn] 7s2 5f14 6d2 Quite unreactive Fairly inactive element Not very reactive Highly radioactive Paper 2, Unit 1, Chapter 1

[Ar] 4s13d5 [Kr] 5s1 4d5 [Xe] 6s1 4f14 5d5 Paper 2, Unit 1, Chapter 1

d-BLOCK ELEMENTS No. of lectures – 12 Term - 1

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