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

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d-BLOCK ELEMENTS

No. of lectures – 12Term - 1

1smitaasthana@yahoo.com

Paper 2, Unit 1, Chapter 1

INTRODUCTION OF D-BLOCK INTRODUCTION OF D-BLOCK ELEMENTSELEMENTS

2smitaasthana@yahoo.com Paper 2, Unit 1, Chapter 1

Periodic TablePeriodic Table

f block transition elements

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 IIBVIIIB

d-Block Transition Elementsd-Block Transition Elements

Most have partially occupied d sub-shells in common oxidation states

Why are they called d-block Why are they called d-block elements?elements?

Their last electron enters thed-orbital.

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.

What is a transition What is a transition metal?metal?• For this reason, a transition a transition

metal is defined as being metal is defined as being an an element which forms at least element which forms at least one ion with a partially filled d one ion with a partially filled d orbital(s).orbital(s).

The d block:The d block:

• The d block consists of three The d block consists of three horizontal series in periods 4, 5 & 6horizontal series in periods 4, 5 & 6– 10 elements in each series10 elements in each series– Chemistry is “different” from other Chemistry is “different” from other

elementselements– Differences within a group in the d Differences within a group in the d

block are less sharp than in s & p blockblock are less sharp than in s & p block• Similarities across a period are greaterSimilarities across a period are greater

Electronic ArrangementElectronic ArrangementElement

Z 3d 4s

ScSc 2121 [Ar][Ar]

TiTi 2222 [Ar][Ar]

VV 2323 [Ar][Ar]

CrCr 2424 [Ar][Ar]

MnMn 2525 [Ar][Ar]

FeFe 2626 [Ar][Ar]

CoCo 2727 [Ar][Ar]

NiNi 2828 [Ar][Ar]

CuCu 2929 [Ar][Ar]

ZnZn 3030 [Ar][Ar]

Electronic Electronic ConfigurationConfiguration• 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

Chromium and CopperChromium 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

Trends in properties

1. Atomic and Ionic radiiDecreases across the series as the atomic no. Increases, due increase in nuclear charge.a) From Sc to Cr - regular expected decrease

Increased nuclear attractionb) From Cr to Ni - almost same size

nuclear attraction = inter electronic repulsion

c) Ni to Zn – Marginal increasenuclear attraction < inter electronic repulsion

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2. Ionization Potential

3. Variable Oxidation 3. Variable Oxidation StatesStates

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⁺

Oxidation States of Oxidation States of TM’sTM’sSc

Ti V Cr

+2 +2 +2 +2 +2 +2 +2 +2 +2 +2

+3 +3 +3 +3 +3 +3 +3 +3

+4 +4 +4 +4

+5 +5 +5

+6 +6 +6

+7 15smitaasthana@yahoo.com

Oxidation States of Oxidation States of TM’sTM’s1. 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

Stability of OS’sStability of OS’s

• General trends1. Higher OS’s become less stable

relative to lower ones on moving from left to right across the series

2. Compounds containing TM’s in high OS’s tend to be oxidising agents e.g MnO4

3. Compounds with TM’s in low OS’s are often reducing agents e.g V2+ & Fe2+

Oxidation States of Oxidation States of TM’sTM’s• 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

Oxidation States of TM’sOxidation States of TM’s• 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 formedare not formed

Oxidising and reducing natureOxidising 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)

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

Formation of coloured ions

Ferromagnetism andFerromagnetism andParamagnetismParamagnetism

smitaasthana@yahoo.com Paper 2, Unit 1, Chapter 1

Magnetic behaviourElectron is a micromagnet, moves 1.On its axis – Spin moment2.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.

[Ar] 4s23d2

[Kr] 5s2 4d2

[Xe] 6s2 4f14 5d2

[Rn] 7s2 5f14 6d2

Quite unreactive

Fairly inactive element

Not very reactive

Highly radioactive

Titanium

Zirconium

Hafnium

Rutherfordium

[Ar] 4s13d5

[Kr] 5s1 4d5

[Xe] 6s1 4f14 5d5

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

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