13.1) PHYSICAL PROPERTIES OF FIRST ROW TRANSITION ELEMENT

A TRANSITION ELEMENT IS STRICTLY DEFINED AS AN ELEMENT THT FORMS AT LEAST A STABLE SIMPLE ION WITH INCOMPLETE OR PARTIALLY FILLED d ORBITALS

PARTIALLY MEANS NEITHER EMPTY NOR FULL

TRANSITION ELEMENT AND THEIR IONS

Sc Ti V Cr Mn Fe Co Ni Cu Zn

Transition metal

d- block element

Scandium and zinc are not transition elements based on the chemical definition given. Each of these metals forms just one ion.

Sc : [Ar] 3d¹ 4s² Sc³⁺ : [Ar} (empty 3d subshell)

Zn: [Ar] 3d¹⁰ 4s² Zn²⁺: [Ar] 3d¹⁰ (full 3d subshell)

Atomic size

• The decrease in atomic size does not apply to the d-block elements

• Atomic size of the 1st row d-block elements are shown in table 1. With the exception of scandium and titanium, the atomic radius of the d-block elements are approximately the same across the period.

• In the series of 1st row d-block elements, additional electrons go into an inner electron shell (3d subshell). At the same time, the number of the electrons in the outermost shell) (4s orital) remain constant.

Table 1Element (symbol) Proton number Electronic

configurationAtomic radius (nm)

Scandium (Sc) 21 [Ar] 3d¹ 4s² 0.160

Titanium (Ti) 22 [Ar] 3d² 4s² 0.146

Vanadium (V) 23 [Ar] 3d³ 4s² 0.131

Chromium ( Cr) 24 [Ar] 3d⁵ 4s¹ 0.125

Manganese (Mn) 25 [Ar] 3d⁵ 4s² 0.129

Iron (Fe) 26 [Ar] 3d⁶ 4s² 0.126

Cobalt (Co) 27 [Ar] 3d⁷ 4s² 0.125

Nickel (Ni) 28 [Ar] 3d⁸ 4s² 0.124

Copper (Cu) 29 [Ar] 3d¹⁰ 4s¹ 0.128

Zinc ( Zn) 30 [Ar] 3d¹⁰ 4s² 0.133

These inner 3d electrons shield the outer 4s electrons from the nuclear charge much more effectively than outer shell electrons can shield one another thus,the effect of increased nuclear charge is roughly cancelled by

screening effect of the electrons in the 3d orbitals. This means tht the effective nuclear remains almost constant. Thus, the atomic (metallic) radii do not change very much for the first row d-block elements. (figure 1)

Sc Ti V Cr Mn Fe Co Ni Cu Zn0

20

40

60

80

100

120

140

160

180

atomic radius

atomic radius

Melting and boiling point• At the 1st row d-block elements except (zinc) have high melting points and boling points

(figure 2) because of strong metallic bonds in the metal lattice.

Sc Ti V Cr Mn Fe Co Ni Cu Zn0

500

1000

1500

2000

2500

3000

3500

4000

boiling pointmelting point

Small energy difference between the electrons in the 3d and 4s subshells enables these electrons to contribute to the ‘sea of delocalised electrons’ and hence results in strong metallic bonding. In contrast,potassium from the same period is soft and has a low melting point of 64⁰C and boiling point of 774⁰C as only one 4s electron is involved in the metallic bond formation. similarly, calcium has relatively low melting point(840⁰C) and boiling point (1484⁰C).

Melting point and boiling point of manganese and zinc are lower-extra stability of the half-filled and completely filled d subshell. These d electrons are less available, leaving only the 4s electron to contribute to the ‘sea of delocalised electrons’ in metallic bonding.

Densities

The densities of the first series d-block elements increase from scandium to copper and then dips for zinc.

element Sc Ti V Cr Mn Fe Co Ni Cu Zn

density 3.00 4.51 6.10 7.19 7.43 7.86 8.90 8.90 8.96 7.14

This means the densities of d-block elements are high compared with other metals ( for example, group 1 and 2 elements). The high densities of these elements –relatively small atomic radii of their atoms. – as a results, the atoms are tightly packed together in the crystal lattice.

When across the 1st row d-block elements, the density increases gradually as shown in figure 3.

Sc Ti V Cr Mn Fe Co Ni Cu Zn0

1

2

3

4

5

6

7

8

9

10

density

density

In passing from scandium ( metallic radius=0.160 nm) to copper (metallic

radius= 0.128 nm), there is a slight decrease in atomic radius. As density=mass over volume, the slight decrease in atomic radius together with an increase in relative atomic mas causes the increase in density.

Successive Ionisation Energies

• The 1st and 2nd ionisation energies of the first series d-block elements increase slightly across the series as the poton numbers increases.(figure 4)

Sc Ti V Cr Mn Fe Co Ni Cu Zn0

1000

2000

3000

4000

5000

6000

7000

8000

1st ionisation energy2nd ioniation energy3rd ionisation energy4th ionisation energy

• In forming M⁺(g) ions (1st ionisation energy) and M²⁺(g)ions (2nd ionisation energy)of the d-block elements,the 4s electrons are the first to be removed.the slight increase in the 1st and 2nd ionisation energies on going across d-block series – bcause the 4s electrons are shielded frm the increasing nuclear charge by the increasing screening effect of the inner 3d electrons.

• The 2nd ionisation energies for chromium and copper is higher than expected-bcause the 2nd electron is removed from 3d⁵nand 3d¹⁰ orbitals respectively. Half-filled d orbital (d⁵)and fully filled d orbital (d¹⁰) have extra stability. A higher energy is required to remove electrons from these orbitals.

3s 3p 3d 4s• Cr• 2nd electron removed from the 3d orbitals

3s 3p 3d 4s• Cu

• 2nd electron removed from the 3rd orbitals

• The 3rd and 4th ionisation energies from scandium to zinc show a larger increase.

- Because the electrons in 3d orbitals are now being removed.

- The remaining electrons gives a relatively smaller shielding effect.

- The effective nuclear charge (increasing nuclear charge and decreasing shielding effect) increases more significantly frm one element to the next across the d-block elements.

• The 3rd ionisation energy of manganese (3260kJ mol¯¹) is higher than tht of chromium (2990 kJmol¯¹) and iron (2960 kJmol¯¹) because the 3rd electron is removed from the stable Mn²⁺ ion which has the electronic configuration [Ar] 3d⁵. Similarly for Zn, more energy is required to remove an electron from the stable Zn²⁺ion with the electronic configuration [Ar] 3d¹⁰.

• The 4th ionisation energy of scandium is very high- bcause 4th electron must be removed frm the inner sub-shell of a stable noble gas configuration.

• The 4th ionisation energy of titanium (4170 kjmol¯¹) is very much lower than of the scandium(7110 kjmol¯¹)-bcause the 4th electron is removed from the d-orbitals and not from the full p orbitals of a noble gases.

• The successice ionisation energies for a given metal in the d-block series increases gradually- bcause the electrons in the 4s and 3d sub-shells differ only slightly in terms of energy level.

• For example:750(1st),1960,3560,5690(4th ionisation energy)

Bcause of this, an atom of d-block element can lose electrons from both the outer 4s and inner 3d sub-shells to form ions

CHEMICAL PROPERTIES OF

TRANSITION ELEMENTS.

Ti

• +2• +3• +4

V

• +2• +3• +4• +5

CR

• +2• +3• +4• +5• +6

Mn

• +2• +3• +4• +5• +6• +7

Fe

• +2• +3• +4• +5• +6

Co

• +2• +3• +4• +5

Ni

• +2• +3• +4

Cu

• +1• +2

1) Exhibit variable oxidation state.

- due to the small difference of energy (small gap) between the 4s and 3d subshell, electrons are able to transfer from 4s to 3d easily. Therefore, transition elements have variable oxidation state.

Oxides of transition elements.

Ti

Ti2O3

TiO2

V

V2O3

V2O5

Cr

Cr2O3

CrO3

Mn

MnO

MnO2

Mn2O3

Mn2O7

Fe

FeO

Fe2O3

Co

CoO

Co2O3

Ni

NiO

NiO2

Cu

CuO

Cu2O

- Insoluble in water.- Covalent character.

2) Forms complexes.

- Forms oxoanions.

Oxoanions- formed due to high charge densities of ionisation.

- Simple ions: low oxidation states; ex: +1,+2,+3- Usually form basic electrovalent oxides.

- Whereas, oxidation states of +4 to +7 do not form simple ions.

- Usually form acidic covalent oxides, except for +4, it is amphoteric.

Ti

TiO2+

VVO2+

VO2+

VO3+

Cr

CrO42-

Cr2O72-

Mn

MnO4-

MnO42-

Fe

FeO42-

Oxoanions. (complex ions)

+2 and +3 Oxidation states.

The relative stability of the oxidation state

• Most oxidation states of the transition elements are +2 & +3

• Ti , V , Cr & Fe +3 oxidation state is more stable than +2 oxidation state

• Mn , Co , Ni & Cu +2 oxidation state is more stable than +3• Because , as go across the d block , it gets more difficult to

remove a third e-• Due decrease in size of the atom & increase in nuclear

charge• Oxidation state +4 and above are relatively less stable

because energies involve too high

Standard Reduction Potentials & the Relative Stability of Aqueous Ions

• Most oxidation states of transition element are +2 & +3.

• Relative stability of +2 & +3 states can predict by looking at the standard electrode potential.

• Refer to graph page 223 no.3• Half- cells where the E values are less than +1.23V,

oxygen from air will oxidize the +2 state to +3 state ( pg. 223 no 4 e.g..)

• Half-cells where the E is more positive than +1.23V , the +3 than +2 state( pg. 223 no 5 e.g..)

Redox properties of the various oxidation state

• Lower oxidation states of transition elements are reducing as shown by their negative standard electrode potentials.

• The more positive the E value , the stronger the oxidizing agent.

• Refer to (pg. 224 no 2-4)

3) Form coloured ions.

Why are ions of transition elements coloured?- Their d-subshell is partially filled with electrons.

dxy dxz dyz dx2

y2 dz

2

dx2

y2 dz

2

dxy dxz dyz

E

WHEEL OF COMPLEMENTARY COLOURS.

4) Act as a catalyst.

Catalyst can be divided into two types:

- Homogeneousthose in the same physical phase as the other reactants e.g: all in solution together in the same solvent, or all are gases.

Most transition elements are effective homogenous catalys.Because: 1)oxidation able to interconvert readily.

2) 4s and 3d orbitals are close in terms of energyTherefore, transition elements are useful as redox catalysts.

- Heterogenousthose in a different physical phase to the rest of the reactants. e.g: two different liquids in contact with catalysis occurring at the interface between them, or more commonly a solid catalyst and a solution, or a solid and gases

Occurs on the surface of the solid.Transition elements are effective heterogenous because:1) have many empty 3d and 4s orbitals; can form temporary bonds with the reactant molecules.

Mechanism:- adsorption of reactants onto the surface of catalyst- breaking and formation of bonds- desorption of products from the surface of the catalyst

5) Paramagnetic.

- Because transition elements have unpaired electrons.- Weakly attracted by external magnetic field.- Strength of paramagnet is affected by the number of unpaired

electrons.Strength of paramagnet increase as the number of unpaired electrons increase.

p/s: paramagnets always point permanently to the poles of the Earth (compass)

Formation of Complex Ions and Ligand Exchange

• A complex ion = an ion of a central metal cation bonded to a group of atoms/ molecules / ions (ligand) by coordinate bonds

• Eg. of complex ion (Cu(NH3)4)2+ • Formation of complex, the ammonia molecule

donate their lone pair electrons to empty orbitals in Cu2+ ion to form coordinate bonds

• The metal cation acts as Lewis acid & ammonia molecule acts as Lewis base

13.3 NOMENCLATURE

AND BONDING OF COMPLEXES.

NAMING OF COMPLEXES

• A ligand or complexing agent , is a polar molecule or ion bonded to a central metal ion.• A complex ion is a polyatomic species consisting of a central metal ion surrounded by

several ligands.• Naming complex ion: a) anionic ligands have names ending in ‘o’. i) ‘ide’ ‘o’. E.g: chloride= chloro b)Neutral ligands are named as the molecule with these notable exceptions: i)H₂O= aquo ii)NH₃= ammine c)the number of ligands in a complex are specified using prefixes: i)di = 2 ii)tri = 3 iii) tetra = 4 iv)penta = 5 v) hexa = 6

• The ligands are named first (prefix), in alphabetical order followed by the name of the metal ion, all in one word with no space between them.

• Oxidation number of metal cation is written in Roman numerals with a bracket after the metal cation’s name.

prefix + metal ion name + oxidation number

• The name of an anionic complex ion ends in ‘ate’, ex: Titanium = titanate

• The prefix bis,tris and tetrakis are used to replace di, tri and tetra if a ligand itself already has the later prefix.

Ex: [ Ni(C₂ ₄)₃]⁴⁻ =𝑂 TRIS-ETHANEDIOATENICKELATE (II)

• Example: Name the following complex ion: [Fe(CN)₆]^3-

1.The overall charge on the ion is negative, so the metal name becomes ferrate.

2.The oxidation number needs to be worked out considering that the cyanide ion has the formula CN-. There are six cyanide ions = 6-. The overall charge on the complex ion is 3- therefore the metal ion has a charge of [3- = x+ (6(-1))],i.e. oxidation state (III)

There are six cyanide ions, therefore hexacyano-

The complex ion's name is hexacyanoferrate (III)

BONDING OF COMPLEXES• In formation of complexes,

central metalis cation uses its empty orbitals in valence shell to accept lone pair electron

from the ligand to form coordination.• Ex: hexacyanoferrate (II) complex ion [Fe(CN)6]^4-.

Electronic configuration of Fe^2+ = [Ar]3d6. 3d 4s 4p1st step : pairing of electrons2nd step: empty orbitals used to accept lone pairs.

↿⇂ ↿ ↿ ↿ ↿

CLASSIFICATION OF LIGANDS• Ligand have lone pair electrons that can be donated to a metal cation to

form coordinate bonds.• Classified according to no of lone pair that can be donated to central

metal cation.• 3 types: i)monodentate ligand ii)bidentate ligand iii)hexadentate ligand

MONODENTRATE LIGANDi. Has one donor atom ii. forms one coordinate bond per unit ligand.iii. The term "monodentate" can be translated as "one tooth," referring to the

ligand binding to the center through only one atom. iv. Ex: H O ₂ , water (referred to as aqua when it is a ligand)

BIDENTATE LIGAND

i. Have 2 donor atoms

ii. Form 2 coordinate bond oer unit ligand

iii. Ex: Ethane-1,2-diamine

H₂N CH₂ CH₂ NH₂ Nitrogen atoms on the edges have two free electrons that can be

used to bond to a central metal ion

iv) Bidentate ligand can form ring like structure. These ligand known as chelating agents and the complexes

are called chelate compounds/chelates.

HEXADENTATE LIGANDiv. EDTA or ethylenediaminetetraacetate is a hexadentate ligand whc is used in its

anionic form EDTA^4-.

v. Have 6 donor atom.

GEOMETRY COMPLEXES

• General geometry depend on no of coordinate bond surrounding central metal cation.• Coordination number: no of coordinate bond surrounding cental atom.

Coordination number of 2• Linear • Ex: [CuCl ] # : Cl Cu Cl₂ ⁺

Coordination number of 4• Tetrahedral• Different geometries are dur to different type of hybridisation.• Tetrahedral: sp^3 hybrisation • Square plannar : dsp^2 hybridistion

COORDINATION OF NUMBER 6• octahedral

Square plannar tetrahedral

octahedral

Uses of chromium• increase tensile strength of steel and increase steel’s resistant to corrosion by forming oxide

layer.• Alloy of chromium with vanadium and tungsten is used in high speed cutting tools.• Make electrical heating elements• Several chromium compounds are used as catalysts for processing hydrocarbons. For

example the Phillips catalyst, prepared from chromium oxides, is used for the production of about half the world's polyethylene

Uses of titanium• Lighter than steel and more resistant to corrosion• Titanium(IV) oxide white solid used as white pigmnt in paints.

Uses of Manganese and Cobalt• main use in manufacture if alloys• Used to make speed cutting tools.• Alloy of cobalt and samarium (Sm) is used to make permanent magnets.

USES OF FIRST ROW TRANSITION ELEMENTS

1) Widely used in alloys.2) Used in making aircrafts, space capsules and nuclear

reactor.3) Used in hip and knee replacement units and also bone

implants4) Chromium used in electroplating and also high speed

cutting tools5) Nichrome used as electrical heating element.6) Used to make stainless steels (alloy) 7) Cobalt-60 (isotope) used as radiation for cancer

treatments.8) Nickel used as catalyst in the production of margarine.9) Cupro-Nickel used for making coins.10) Alnico used to make strong permanent magnets.11) Copper used in electrical wiring12) Copper used in domestic hot water pipes.