Chemistry of Transition and Inner Transition Elements+

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Transition elements [d[d- block elements]

Position in the periodic table

20_431

Sc Y La

Ti Zr Hf

V Nb Ta

Cr Mo W

Mn Tc Re

Fe Ru Os

Co Rh Ir

Ni Pd Pt

Cu Ag Au

Zn Cd Hg

Ac Unq Unp Unh Uns Uno Une Uun Uuu

Ce Th

Pr Pa

Nd U

Pm Sm Np

Eu

Gd

Tb

Dy Cf

Ho

Er

Tm

Yb No

Lu Lr

Pu Am Cm Bk

Es Fm Md

Where are the transition metals?The transition metals are the block of elements located between group 2 and group 13 of the periodic table. group 2 group 13

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 Ac Rf Db Sg Bh Hs Mt Ds Rg ?

Here, the word transition is used to mean in-between.

Why transition metals are called typical metals?The transition metals are known as typical metals because of their physical properties. They are: lustrous (bright and shiny). hard and strong. high density. malleable (can be bent and pressed into different shapes) and ductile (can be drawn into wires). good conductors of heat and electricity. high melting and boiling points (except mercury, which is liquid at room temperature).

All 'd' block elements are classified into four transition series namely: 3d series in the 4th period 10 elements 4d series in the 5th period- 10 elements 5d series in the 6th period- 10 elements 6d series in the 7th period having incomplete elements.

GENERAL PROPERTIES OF TRANSITION ELEMENTS

All the elements belonging to I B, II B, III B, IV B, V B, VI B, VII B, VIII B (i.e.3 TO 12) are called transition elements. They resemble each other in several physical and chemical properties. They are all metals. They are called transition elements because they are placed between the most reactive metals on the left and nonnon-metals on the right. Their compounds are colored. They exhibit variable valency. They form co-ordination compounds. coTend to be hard and durable. Have high tensile strength. Have good mechanical properties.

Electronic Configuration

General outer electronic configuration is (n - 1) d1-10 ns1-2. Each additional electron enters the (n-1) sub-shell. (n- sub 'd' block elements are those in which the added electron goes into one of the 'd' orbitals. These elements have valence electrons in both their outermost and penultimate shells (second outermost)

Energy

4p 3d

4s 3p 3s 2p 2s

1s

Sc -1s2 2s2 2p6 3s2 3p6 3d1 4s2

Electronic ArrangementElSc Ti V Cr Mn Fe Co Ni Cu Zn

Z21 22 23 24 25 26 27 28 29 30 [Ar] [Ar] [Ar] [Ar] [Ar] [Ar] [Ar] [Ar] [Ar] [Ar]

3d

4s

Chromium and CopperCr and Cu dont fit the pattern of building up the 3d sub-shell, why? sub-

CHROMIUM

Energy

4p

4s 3p 3s 2p 2s

3d

1s

Cr-1s2 2s2 2p6 3s2 3p6 3d5 4s1

Energy

4p

4s 3p 3s 2p 2s

3d

1s

Cu-1s2 2s2 2p6 3s2 3p6 3d10 4s1

GENERAL CHARACTERISTICS OF TRANSITION ELEMENTSThe members belonging to a given transition series do not differ so much from one another as those of representative elements of the same period. It is due to as there is no change in the number of ns electrons and only change occurs in the (n(n- 1)d electrons from member to member in a period.

Sc3+ and Zn2+ are not the typical TM ions Not all d block elements have incomplete d sub-shells. sub e.g. Zn has e.c. of [Ar]3d104s2, the Zn2+ ion ([Ar] 3d10) is not a typical TM ion Similarly Sc forms Sc3+ which has the stable e.c of Ar. Sc3+ has no 3d electrons

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 sub-shell of d electrons. sub In period 4 only Ti-Cu are TMs! Ti Note that when d block elements form ions the s electrons are lost first

1. Metallic characterMost of the transition elements of the first row form metallic bonds due to the presence of incomplete outermost energy level. So, all the transition elements exhibit metallic characters. The strength of the metallic bond depends upon the number of unpaired d-electrons. As the number dincreases the strength also increases. Due to the absence of unpaired electrons 'Zn' is not a hard metal.

Hg exists as a liquid at room temperature Mercury has completely filled d10 electronic configuration. Hence the extent of metallic bond formation is less as the orbitals are completely filled. due to weak interatomic forces of attraction, Hg exists as a liquid at room temperature(Downward trend in melting points from Zn (420C) (420 through Cd (321 C) to Hg (-39 C) (-

2. Atomic and Ionic radiiAtomic radii: In the transition elements the atomic radii decreases with increase in atomic number. At the end of series it slightly increase due to increase in electron-electron repulsion. electronThe atomic radii of 4-d and 5-d series are very 45close due to lanthanide contraction.

Atomic radii :20_435

0.2 La 1st series (3 d ) Y Atomic ra dii (n m) Hf Zr 2nd series (4 d) 3rd series (5 d) Ta Nb W Mo Au Ag Ir Rh Mn Fe Co Pt Pd Ni Cu

Sc 0.15 Ti

Re Tc

Os Ru

V Cr

0.1 Atomic number

Ionic radii: In the first row transition elements the ionic radii decreases with increase in atomic number. The value of ionic radii also depends on the oxidation state of metals. As the oxidation state increases the ionic radii decreases (nuclear pull increase)and as the oxidation state decreases the ionic radii increases.

3. Colored ionsIn the first row transition elements all the elements except Zn form colored ions. As these elements have incomplete d-orbital, some amount dof energy is required to promote the electrons from lower energy level to higher energy level. This process exhibits radiations from which the compounds absorb a particular color. But some elements other than Zn also appear colorless depending on their oxidation state. For e.g., Sc3+, Ti4+ and Cu+ have completely filled d-orbitals and hence they dappear colorless.

Most of the transition elements form colored compounds both in solid state as well as in aqueous solution. It is already studied that the transition metals have incomplete d-orbital. The electrons are to dbe promoted from a lower energy level to a higher energy level. Some amount of energy is required for this process and the radiations of light are observed in the visible region. The compounds absorb a particular color from the radiation and the remaining ones are emitted. For e.g., Cu2+ are bluish green in color due to absorption of red light wavelength. As Zn has completely filled d-orbitals it cannot absorb dradiation and hence Zn2+ salts are white.

Most transition metals form coloured compounds. For example: Iron (II) oxide (FeO2) is black.

Iron (III) oxide (Fe2O3) is red/brown when hydrated this is rust. Copper (II) sulfate crystals (CuSO4.H2O) is blue these can be turned white by heating the crystals to remove the water.

Copper (I) oxide Cu2O is red/brown.

Copper (II) oxide CuO is black.

Color and Magnetism

Electrons in partially filled d sublevel absorbs visible light , moves to slightly higher energy d orbital.

Magnetic properties are due to unpaired electrons.

4. Complex formationAll the first row transition elements form complexes. These complexes contain negative ions or neutral molecules linked to a metal ion. These are called as ligands. Some examples of the complex compounds formed by first row transition elements are: As the transitions metals are small in size they form large number of complexes. [Fe(CN)6]4[Fe(CN)6]4-, [Cu(NH3)4]2+, [Ni(CN)4]2-, [Ni(CN)4]2[Zn(NH3)4]2+32+2+

5. Variable Oxidation StateThe transition elements show variable oxidation states. By the study of electronic configuration of transition metals it is understood that variable oxidation state can be formed as there are both ns and (n-1)d (nelectrons in bonding. bonding. The participation of ns electrons in bonding leads to +2 oxidation state which is a lower oxidation state. The participation of (n-1)d electrons in bonding leads to higher oxidation (nstates like +3, +4, +5, +6 etc. These oxidation states depend upon the nature of combination of transition metals with other elements. The oxidation state increases with atomic number. This increase is related to groups. The most common oxidation state of the elements of first transition series is +2. Ionic bonds are formed in lower oxidation state transition elements whereas covalent bonds are formed in higher oxidation states. Zn is an exception among them as it has fully filled d-orbital, it exhibits only d+2 oxidation state. The oxidation states of first row transition metals are shown below.

Oxidation States of TM sSc Ti V+2 +3 +3 +4 +3 +4 +5 +6 +6 +7 +6

Cr+2 +3

Mn+2 +3 +4

Fe+2 +3

Co+2 +3

Ni+2 +3

Cu+1 +2 +3

Zn+2

Oxidation States of TM s

Stability of OS sChange from one OS to another is a redox reaction Relative stability of different OS s can be predicted by looking at Standard Electrode Potentials E values

Stability of OS sGeneral 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+

Stability of OS sGeneral trends (continued) Relative stability of +2 state with respect to +3 state increases across the series For compounds early in the series, +2 state highly reducingE.g. V2+(aq) & Cr2+(aq) strong reducing