Transition Metals: Properties and Trends

• D-block elements are in groups 3-12 of the periodic table.
• D orbitals are progressively filled in the four long periods.
• The d-orbitals of the penultimate energy level receive electrons.
• This gives rise to the three rows of the transition metals (3d, 4d, and 5d series).
• The general electronic configuration is (n-1)d¹⁻¹⁰ns¹⁻².
• "(n-1)" stands for the inner d orbitals, which may have 1-10 electrons, in the outermost ns orbital.
• It may have one or two electrons.
• Transition elements have three main series; 3d, 4d, and 5d.
• 3d series includes elements Sc to Zn.
• 4d includes Y to Cd.
• 5d series includes La to Hg, except Ce to Lu.
• A 6d series starts from Ac to Cn (Copernicium), except Thorium to Lawrencium

d Orbital Properties

• Electrons in d-orbitals project to the periphery of an atom.
• The d-orbitals are more influenced by the surroundings.
• They affect surrounding atoms or molecules.
• Partly filled d orbitals show a variety of oxidation states e.g. +2, +3.
• They form coloured ions (d-d transition).
• They enter into complex formation with a variety of ligands.
• Transition metals and compounds exhibit catalytic property and paramagnetic behavior.
• There are greater horizontal similarities in transition elements.
• This is in contrast to the main group elements.
• All transition elements contain an incompletely filled d-subshell, while the outer shell electronic configuration remains the same.

f-Block Element Properties

• F-block elements are those in which the 4f and 5f orbitals are progressively filled.
• They're taken from group 3 of the periodic table to form a separate f-block.
• F block elements are known as inner transition metals.
• The two series of inner transition metals, (4f and 5f) are called lanthanoids and actinoids, respectively.
• The f-block consists of the two series: lanthanoids (the fourteen elements following lanthanum) and actinoids (the fourteen elements following actinium).

Lanthanoids

• Lanthanum closely resembles the lanthanoids.
• It is included in discussions of the lanthanoids, signified by the general symbol Ln.
• The discussion of the actinoids includes actinium besides the fourteen elements constituting the series.
• The general electronic configurations is ns² (n-1)d⁰⁻¹ (n-2)f¹⁻¹⁴.
• A transition element is defined as one which has incompletely filled d orbitals in its ground state or any one of its oxidation states.

Transition Metals

• Zinc, cadmium, and mercury of group 12 have full d¹⁰ configurations in their ground state.
• They also have the same configurations in common oxidation states.
• They are not regarded as transition metals.
• The electronic configurations of Zn, Cd, and Hg are represented by the general formula (n-1)d¹⁰ns².
• Being the end members of the three transition series, the chemistry of Zinc, cadmium, and mercury studied along with the chemistry of the transition metals.
• The d-block occupies the large middle section flanked by "s" and "p" blocks in the periodic table.
• "Transition" is due to the position between s- (highly metallic elements) and p– block elements (mainly non-metals).
• The change between metallic and non-metallic character takes place through this series.

Electronic Configuration

• The electronic configuration of Cr in the 3d series, has 3d⁵4s¹ instead of 3d⁴4s².
• The energy gap between the two sets (3d and 4s) of orbitals decreases and stability is better

Series Configurations

• 1-series: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn
• Atomic No-Z: 21, 22, 23, 24, 25, 26, 27, 28, 29, 30
• 4s: 2, 2, 2, 1, 2, 2, 2, 2, 1, 2
• 3d: 1, 2, 3, 5, 5, 6, 7, 8, 10, 10
• 2-series: Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd
• Atomic No-Z: 39, 40, 41, 42, 43, 44, 45, 46, 47, 48
• 5s: 2, 2, 2, 1, 1, 1, 1, 0, 1, 2
• 4d: 1, 2, 4, 5, 6, 7, 8, 10, 10, 10
• 3-series: La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg
• Atomic No-Z: 57, 72, 73, 74, 75, 76, 77, 78, 79, 80
• 6s: 2, 2, 2, 2, 2, 2, 2, 1, 1, 2
• 5d: 1, 2, 3, 4, 5, 6, 7, 8, 10, 10
• 4 series: Ac, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Uub
• Atomic No-Z: 89, 106, 105, 104, 103, 102, 101, 100, 99, 98
• 7s: 2, 2, 2, 2, 2, 2, 2, 2, 1, 2
• 6d: 1, 2, 3, 4, 5, 6, 7, 8, 10, 10

Metallic element properties

• Transition elements display metallic properties, such as high tensile strength, ductility, malleability, high thermal and electrical conductivity, and metallic luster.
• Zn, Cd, Hg and Mn are exceptions.
• Most transition elements have one or more typical metallic structures at normal temperatures.
• Transition elements have low volatility due to high atomization enthalpy; and very high melting and boiling points.
• The high melting points of these metals are attributed to the involvement of greater number of electrons from (n-1)d in addition to the ns electrons in the interatomic metallic bonding.
• A large number of unpaired electrons is favorable for strong interatomic interaction.
• In a row of d block elements, Cr, Mo, W has maximum melting points. Due to unpaired electrons being favorable for strong inter atomic interaction
• Enthalpy of atomization determines the standard electrode potential of a metal.
• Metals with very high enthalpy of atomization (i.e., very high boiling point) tend to be noble in their reactions (less reactive).
• The metals of more frequent series have greater enthalpies of metal – metal bonding in compounds of the heavy transition metals
• This is in turn is due to involvement of electrons of ns and (n-1)d orbital as they are held less strongly by the nucleus as atomic size increases down the group.

Varying Atomic Properties

• Ions of the same charge decrease in radius with increasing atomic number.
• This is because the new electron enters a d orbital each time the nuclear charge increases by unity. Shielding is not that effective
• The radii of the third (5d) series are similar to the second (4d) series.
• Phenomenon with Lanthanoid contraction compensating for expected increase in atomic size.
• The steady decrease in atomic and ionic size of lanthanide elements with increasing atomic no due to poor shielding of 4f electrons is called lanthanoid contraction.
• Consequences of lanthanoid contraction:
  • second and third d series exhibit similar radii (e.g., Zr 160 pm, Hf 159 pm)
  • have very similar physical and chemical properties more than that expected
  • results in their joint occurrence in nature
  • difficulty in separation.
• It is difficult to separate lanthanoid elements due to similar chemical properties.
• Basicity decreases from La(OH)3 to Lu(OH)3 due to the decrease in metallic radius coupled with increase in atomic mass, resulting in a general increase in the density of these elements. (density = mass /volume).
• From titanium (Z = 22) to copper (Z = 29), there is a significant increase in the density.
• Atomic radii increase towards the end of each series because d and s subshells are completely filled due to electron electron repulsion, thus increasing their radii.

Ionization Enthalpies

• Nuclear charge leads to rise in ionization enthalpy along each series of the transition elements from left to right.
• The first ionization enthalpy increases as the effective nuclear charge increases.
• The value of first ionization enthalpy may be lower for Cr because of the absence of any change in the d configuration.
• The value for Zn may be higher because it represents ionization from the 4s level.
• Elements do not increase as steeply.
• The removal of one electron alters the relative energies of 4s and 3d orbitalsSo the dipositive ions have a configurations with no 4s electrons. -Reorganization occurs with some gains in exchange energy as number of d electrons increases
• Irregular trend in first ionisation of 3d metals
• Unusual extra stability of d, d half filled t2g stability
• The lowest common oxidation state of 3d series metals is +2, except Cu with +1.
• M2+ ions require the sum of the first and second ionisation energies in addition to the enthalpy of atomisation for each element.
• Second ionisation has high values for Cr and Cu
• disruption causes considerable loss of exchange energy with Presence of half filled and completely filled d orbital cause second ionization
• As the ionisation consists of the removal of an electron which allows the production of the stable d¹⁰ configuration. [Ar]184s⁰3d¹⁰
• The trend in the third ionisation enthalpies is high
• Greater difficulty of removing an electron from ½ filled and do completely
• The lowest common oxidation state of 3d series metals is +2, except Cu with +1.

Variable Oxidation States of Transition Elements

• Both ns and (n-1) d electrons are involved in the bonding as there is no much energy difference between them.
• The elements which give the greatest number of oxidation states occur in or near the middle of the series i.e. Manganese for example
• The difference in oxidation in transition elements increases by unity and in non transition elements they normally increase by a unity of two. The variability in the oxidation of transition states comes from the incomplete filling of d orbitals whereas . In the d-block, the higher oxidation states are favored by the heavier members. In the p-block, the tower oxidation states are favored by heavier members (due to inert pair effects)-. Low oxidation states occur w complex compound with ligands

Oxidation

• Titanium (IV) is more stable [Ar] 184s°3d° (noble gas configuration).
• The only oxidation state of zinc is +2 (no d electrons are involved).
• [Ar]184s°3d¹⁰ (completely filled d orbital stability) Mn [Ar] 184s²3d³
• The electron is removed from stable s orbital with complete filling
• Mn¹+ does not exist because first ionization enthalpy is very high.
• +2 oxidation stability because 2nd IE is compartively lower

Electrode Potentials

• The high energy to transform Cu(s) to Cu²+(aq) is not balanced by its hydration enthalpy.
• Hydration enthalpy of Cu²+(aq) is not sufficient to provide very high atomization and first two ionization enthalpy of Cu- Having a positive Ecu²+/Cu accounts for its inability to liberate H₂ from acids.
• Hydrogen is more reactive than Cu- Only oxidising acids (nitric and hot concentrated sulphuric) react with Cu
• The general trend towards less negative E° ²+/M values(less tendancy to undergo oxidation)
• Across the series is related to the general increase in the sum of the first and second ionisation enthalpies
• Mn²+ + oxdises to Mn2+ low sum of first two IE
• Ni ger oxidixsed + negative

Metal Oxidation

• Low E (M³+/M²+) (negative value) for Sc reflects the stability of Se³+ config.
• The highest value E (M³+/M²+) for Zn is due to the from the stable d¹⁰ difficult

Properties

• Diamagnetic substances are repelled by the applied field while
• the paramagnetic substances are attracted
• Substances which are attracted very strongly are said to be ferromagnetic.
• Extreme form of paramagnetism
• unpaird e- = magnetic movement

Unpaired electrons

Transition elements show interstitial compounds (H,C, or N in metal crystal lattices) are usually :

• non stoichiometric
• non ionic/covalent These compounds have:

1. high melting points 2)some borides approach diamond in hardness
2. retain metallic conductivity 4)re chemically inert

Alloys

Alloys may be homogeneous solid solutions. One metal is distributed randomly among the atoms of the other.

• atoms must be are within about 15% of each other.
• Alloys are hard/high melting points. Metals can replace one another in the crystal lattice.

Disproportionation of Oxidation States:

1. a particular oxidation state becomes less stable relative to other oxidation state, one lower,
2. said to undergo disproportionation. For example, manganese (VI) becomes unstable relative to (VII)

Oxide Properties

Oxoanion Mn2O7: Covalent green oil - higher oxides Gives HMnO4 (acidic properties predominates). V2O5: amphoteric though mainly acidic (VO salts with alkalies and VO salts with acids ) V2O3, CrO: Basic V2O4:Less basic

Potassium Dichromate

Potassium dichromate is a important Industry and also an oxidant Generally prepared Chromite Ore Yellow solution -orange sodium. CrO42 is tetrahedral 2 crO42 (high pH) 2Cr4 +2H->Cr,3 + 2H (low pH)

More on Oxidizing Action

Sodium/potassium Oxidizing agent:

• in organic chemistry
• in acidic solution Cr2O7 * 14H* * 6e" ->2Cr2+ + 7HO 1 Potassium permanganate forms dark purple (almost black) crystals which are isostructural with those of KClO4, 1 The salt is not very soluble in water but when heated it decomposes at 513 К: 2KMnO4 K2MnO4+MNO2+2 Oxidising action of Acidify :

Inner Transition Elements

Only one oxidation La(III) and L(III) pounds Actinide chemistry's more complicated Awide range of oxidation Lanthanoids

• Atomic Sizes decreases from left to right This happens more than Irregularity (as in ionization enthalpies) arises mainly from the extra stability First ionisation enthalpies of the lanthanoids Lanthanoids the exchange enthalpy considerations

Explore the distinctive properties of transition metals, including melting and boiling points, enthalpies of atomisation, and metallic bonding. Understand the factors influencing these properties across the d-block elements, like electronic configurations.