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Properties of Transition Metals

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Chemistry

We'll be looking at the common properties of transition metals here. There's a lot to take on board, so be prepared!

Common properties of transition metals

The general properties of transition metals are atomic radius, melting and boiling point, enthalpy of atomisation, metallic character, ionisation enthalpy, variable oxidation state, complex ion formation, formation of coloured compounds and catalytic activity.

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Hold on tight, as there's a lot of information in this article. Read it slowly and make sure you understand the logic behind the properties of transition metals. That will make remembering them much easier.

The atomic radii of the transition metals are smaller than those of the s-block and larger than those of p-block elements.

If you need a refresher of which elements are in the s- and p-blocks, have a look at Periodic Table.

The atomic radii in ppm (parts per million) of 3d-series elements are given below.

Element

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Atomic radii (ppm)

162

147

134

128

130

126

125

123

128

134

The atomic radius of 3d-series elements decreases initially from scandium to chromium, remains almost constant from chromium to copper, then increases towards the end of the series.

Why do the atomic radii of transition metals not follow a perfect trend?

  • The atomic radius initially decreases across the period because as atomic number increases, the atom's nuclear charge increases. The shielding effect of d-shell electrons is so small that net attraction between the nucleus and the outer electrons increases. Consequently, the atomic radius decreases.

  • As the number of d-electrons increases, the screening effect increases. The screening effect counterbalances (neutralizes) the increased nuclear charge. Hence, the atomic radius remains almost constant.

  • At the end of each period, the electron-electron repulsion between the added electrons in the same orbital is greater than attractive forces due to the increased nuclear charge. This results in expansion of the electron cloud, thus the atomic radius increases.

  • Ionic radius decreases with an increase in oxidation number. For the same oxidation state, the ionic radius generally decreases with an increase in nuclear charge.

The melting points of transition metals are high. This is due to a greater number of electrons from the d-subshell being involved in metallic bonding in addition to the s-electrons.

In any row, the melting points of these metals rise to a maximum at the metal with electron configuration d5 (except for the anomalous values of Mn and Tc), then fall regularly as the atomic number increases.

The enthalpy of atomisation (∆Hat) is the enthalpy change when 1 mole of gaseous atoms is formed from its element under standard conditions

In general, the greater the number of valence electrons, the stronger the resultant bonding. Metals with a very high enthalpy of atomisation (i.e., very high boiling point) tend to be relatively unreactive for this reason.

The metals of the second and third series have greater enthalpies of atomisation than the corresponding elements of the first series. This is an important factor in accounting for the occurrence of much more frequent metal-metal bonding in compounds of heavy transition metals.

All the transition elements are metals. They exhibit all the characteristics of metals. They all have high density, hardness, high melting points and boiling points, high tensile strength, ductility, malleability, high thermal and electrical conductivity.

The first ionisation enthalpy of d-block elements lies in between that of s- and p-block elements. The ionisation enthalpy gradually increases with an increase in atomic number along a given transition series, though some irregularities are observed.

Ionisation enthalpy is the amount of energy needed to remove the outermost electron of a mole of atoms in the gaseous state to form one mole of gaseous anions.

The first ionisation enthalpies of 3d-series elements are given below.

Element

Sc

Ti

v

Cr

Mn

Fe

Co

Ni

Cu

Zn

First ionisation enthalpy

631

656

650

653

717

762

758

736

745

906

Why does ionisation enthalpy not follow a perfect trend?

  • The increase in ionisation enthalpy is due to an increase in nuclear charge with an increase in atomic number. This reduces the size of the atom making the removal of outer electrons more difficult.
  • In a given series, the difference in the ionisation enthalpy between any two successive d-block elements is much less than the difference in the case of successive s- and p-block elements.
  • The addition of d-electrons in the d-subshell with an increase in atomic number provides a screening effect. This shields the outer s-electrons from the nuclear pull. This means that the effect of increased nuclear charge and addition of d-electrons tend to oppose each other. Due to this, the ionisation enthalpy shows little variation on moving along a period of d-block elements.
  • The first ionisation enthalpies of Zn, Cd, and Hg are however very high, because of the completely filled d10 s2 electron configurations.

Transition metals exhibit variable oxidation states. The variable oxidation states of transition metals are due to similar energy levels of the s- and d-orbitals. Oxidation states of the first transition elements are given below.

Element

Outer electronic configuration

Oxidation states

Scandium

3d14s2

+3

Titanium

3d24s2

+2, +3, +4

Vanadium

3d34s2

+2, +3, +4, +5

Chromium

3d54s1

+2, +3, (+4), (+5), +6

Manganese

3d54s2

+2, +3, +4, (+5), +6, +7

Iron

3d64s2

+2, +3, (+4), (+5), (+6)

Cobalt

3d74s2

+2, +3, (+4), (+5)

Nickel

3d84s2

+2, +3, +4

Copper

3d104s1

+1, +2

Zinc

3d104s2

+2

Oxidation states within brackets are unstable, while the most common oxidation states are in bold type.

The magnetic properties of a compound are a measure of the number of unpaired electrons it contains. When a magnetic field is applied, we notice that there are two types of substances.

Paramagnetic substances: the substances which are attracted by a magnetic field are called paramagnetic substances. This character arises due to the presence of unpaired electrons.

Diamagnetic substances: The substances which are repelled by a magnetic field are called diamagnetic substances. This character arises due to the fact that all the electrons are paired.

Most of the transition ions or their compounds have unpaired electrons in the d-subshell. Therefore, they are paramagnetic in character. The magnetic character is expressed in terms of the magnetic moment. The larger the number of unpaired electrons in a substance, the greater the paramagnetic character, and the larger the magnetic moment.

The magnetic moment is expressed in Bohr magneton, abbreviated as B.M. It is calculated by using spin only formula µ = √n(n+2).

  • Where n is the number of unpaired electrons and
  • µ is the magnetic moment.
  • The magnitude of this magnetic moment is very small and is measured in the unit called Bohr magneton, μB. It is equal to 9.27 × 10–24 J T-1.

Ion

Outer electronic configuration

Number of unpaired electrons

Magnetic moment (B.M)

Sc3+

3d0

0

0

Ti3+

3d1

1

1.73

V3+

3d2

2

2.84

Cr3+

3d3

3

3.87

Mn3+

3d4

4

4.90

Fe3+

3d5

5

5.92

Co3+

3d6

4

4.90

Co2+

3d7

3

3.87

Ni2+

3d8

2

2.84

Cu2+

3d9

1

1.73

Zn2+

3d10

0

0

The transition metals and metal ions form a large number of complex compounds. In these compounds, a central transition metal ion is bonded to the number of ions or neutral molecules by co-ordinate bonds. Such ions or neutral molecules are called ligands. This is due to the following reasons:

  1. Small atomic size and ionic size.
  2. High nuclear charge.
  3. Availability of vacant d-orbitals to accept one pair of electrons donated by ligands.

Many transition elements and their compounds act as good catalysts for various reactions.

  • Iron-Molybdenum is used as a catalyst in the synthesis of ammonia by Haber’s process.
  • Nickel is used in hydrogenation reactions.

The catalytic activity of transition metals is due to their tendencies to:

  1. Exhibit variable oxidation states.

  2. Form an unstable intermediate compound and provide an alternative path for the reactant with lower activation energy.

  3. Provide a large surface area for the adsorption of the reactant.

  4. Form dative bonds with ligands.

Most of the transition metal compounds are coloured both in their solid-state, as well as in aqueous solutions. The colour of compounds of transition metals is due to:

  • The presence of incomplete d-subshells.

  • The splitting of degenerate orbitals (orbitals having the same energy) into two sets, one of which has lower energy whilst the other has higher energy. This occurs under the influence of ligands.

  • When the ligand approaches the transition metal ion, its d-orbitals lose their degeneracy. They split into two sets of orbitals, one having a lower energy, and the other having a higher energy. This is called crystal field splitting.

Properties of Transition Metals - Key takeaways

  • The atomic radii of the transition metals are smaller than those of s-blocks and larger than those of p-block elements.
  • The melting and boiling points of transition metals are high.
  • The metals of the second and third series have greater enthalpies of atomisation than the corresponding elements of the first series.
  • All the transition elements are metals.
  • The ionisation enthalpy gradually increases with an increase in atomic number along a given transition series, though some irregularities are observed.
  • Transition metals exhibit variable oxidation states.
  • The magnetic properties of a compound are a measure of the number of unpaired electrons in it.
  • Transition elements and their compounds act as good catalysts for various reactions.
  • Most of the transition elements are coloured compounds.

Properties of Transition Metals

Since most of the transition ions or their compounds have unpaired electrons in the d-subshell, this means that they are paramagnetic. In other words, they show magnetic properties.

1. High melting and boiling points

2. Metallic character

3. Strong

4. High thermal conductivity

5. High electrical conductivity

1. Complex ion formation

2. Formation of coloured compounds

3. Variable oxidation states

4. Catalytic activity

Transition metals have different properties due to the fact that they can lose electrons from the inner d-subshell, apart from the outer s-subshell. This means that they also have valence electrons in an inner shell, which is different from other elements which only have valence electrons in their outer shell.

Final Properties of Transition Metals Quiz

Question

Between Ti2+ and V2+, which ion contains more unpaired electrons?



Show answer

Answer

V2+

Show question

Question

Between V2+ and Fe2+, which ion contains more unpaired electrons?


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Answer

Fe2+

Show question

Question

Why do transition metals show magnetic properties?



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Answer

Since most of the transition ions or their compounds have unpaired electrons in the d-subshell, this means that they are paramagnetic. In other words, they show magnetic properties.

Show question

Question

What are five physical properties of transition metals?

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Answer

1. High melting and boiling points

2. Metallic character

3. Strong

4. High thermal conductivity

5. High electrical conductivity



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Question

What are the characteristic properties of transition elements?

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Answer

1. Complex ion formation

2. Formation of coloured compounds

3. Variable oxidation states

4. Catalytic activity



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Question

Why do transition metals have different properties from main-group elements?



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Answer

Transition metals have different properties due to the fact that they can lose electrons from the inner d-subshell, apart from the outer s-subshell. 



Show question

Question

Why do transition metals have variable oxidation states?



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Answer

The variable oxidation states of transition metals is due to the very similar energy levels of the s and d-orbitals, enabling electrons to be lost from both types of orbitals. 



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Question

What is the difference between paramagnetic and diamagnetic substances?



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Answer

Paramagnetic substances are attracted to a magnetic field due to the presence of unpaired electrons, whilst diamagnetic particles are repelled by a magnetic field, due to the fact that all electrons are paired.



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Question

What are complex compounds?



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Answer

Complex compounds are ones in which a central transition metal ion is bonded to a number of ions or neutral molecules by co-ordinate bonds. Such ions or neutral molecules are called ligands. 



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Question

Give an example of the catalytic use of a transition metal.



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Answer

Nickel is used as a catalyst in hydrogenation reactions.



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Question

Why do transition metals form coloured compounds?



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Answer

The colour of compounds of transition metals is due to crystal field splitting.



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Question

Do transition metals have high or low melting and boiling points?



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Answer

High melting and boiling points



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Question

What is enthalpy of atomisation?



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Answer

The enthalpy of atomisation is the enthalpy change involved in breaking the metallic lattice of the crystalline metal into individual atoms.



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Question

Does the ionisation enthalpy increase or decrease across a period?



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Answer

The ionization enthalpy gradually increases with an increase in atomic number along a given transition series (though some irregularities are observed). 



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Question

What are the most common oxidation states of Fe?



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Answer

Fe2+, Fe3+



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