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Transition metals are found in Group 3 to 12 of the periodic table

Forms colored compounds

Has multiple O.S (Oxidation State)

Good catalyst

Based on the IUPAC definition, a transition metal is an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell

Physical properties

•Higher melting point & densities than Group I and II metals

•Harder and stronger than Group I and II metals

•Good conductors of heat & electricity

Chemical properties

• Less reactive than Group I and II metals.

• Variable oxidation states

• Forms coloured compounds

• Forms complex ions

• Shows catalytic activity

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Electron configuration of First Row Transition metals (raam)

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Electron configuration of First Row Transition metals (raam)

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1 orbital —> 2 electrons spinning in opposite directions

The subshells are s,p,d and f

Subshell S —> 1 orbital (2 electrons)

Subshell P —> 3 orbitals (6 electrons)

Subshell D —> 5 orbitals (10 electrons)

Subshell F —> 7 orbitals (14 electrons)

Aufbau Principle

This states that lower energy atomic orbitals are filled by electrons before higher energy ones are filled

The energy of orbitals increase from S to F

There are certain discrepancies such as 4s orbitals being filled first before 3d orbitals

This is mainly due to the fact that 4s orbitals have lower energy levels than 3d orbitals

Forming ions:

When ions are formed, electrons are removed first from 4s orbitals and then from the 3d orbitals.

Hund’s rule

Hund’s rule states that every orbital in a subshell is singly occupied with one electron before any orbital is occupied

All of the electrons in singly occupied orbitals have the same spin (points in the same direction).

Pauli’s exclusion principle

This principle states that an orbital can have a maximum of only 2 electrons and the 2 electrons must have opposing spins

Exceptions to the principles mentioned:

1. Chromium

2. Copper

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Transition metals will form positive ions that have a positive oxidation state (O.S.) by losing electrons. When they form ions, electrons are removed from the 4s subshell before they are removed from the 3d subshell. Transition metals have multiple O.S. meaning they form ions with variable charges. Transition metals are good catalysts due to this property.

The variable O.S. is possible due to the 4s and 3d having very close energy levels. This allows electrons to be removed from either orbital without a huge difference in energy occurring.

Most transition metals have +2 and +3 oxidation states.

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Complex ion

has a metal ion at its centre with a number of other molecules / ions known as ligands

ligands are attached to the central ion by coordinate(dative) bonds

Ligands

neutral molecules / anions that have at least one atom with a lone pair of electrons

Examples: chloro (CI-), cyano (CN-), hydroxo (OH-), aqua (H2O), ammine (NH3)

Coordination number

total number of bonds the metal atom forms with ligands

Ligand exchange

Hexaaquacopper (II) ions [Cu(H₂O)₆]²⁺

Acid

adding concentrated hydrochloric acid

blue colour --> green

[Cu(H₂O)₆]2+ (aq) + 4Cl⁻ (aq) --> [CuCl₄]²⁻ (aq) + 6H₂O (l)

Base

adding excess amounts of ammonia solution

blue --> deep blue

[Cu(H₂O)₆]2+ (aq) + 4NH₃ (aq) --> [Cu(NH₃)₄(H₂O)₂]²⁺ (aq) + 4H₂O (l)

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In transition metal, the d orbital split into two different energy level [Lower and higher energy level]

Absorption of Energy:

When light hits these complexes, electrons can absorb energy to jump from the lower energy level to the higher energy level.

Color Formation:

The specific wavelength (color) of light that is absorbed corresponds to the energy difference between these two levels.

The color we see is the result of the light that is not absorbed; it is the complementary color of the absorbed light.

Energy Difference and Wavelength:

The greater the energy difference between the lower and higher energy levels, the more energy (shorter wavelength) is needed for an electron to make the jump.

Higher energy transitions correspond to shorter wavelengths, while lower energy transitions correspond to longer wavelengths.

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Catalysts are chemical substances that increase the rate of reaction without itself undergoing any permanent physical change.

Transition metals and their compounds function as catalysts either because of their ability to change oxidation state or, in the case of the metals, to adsorb other substances on to their surface and activate them in the process.

Types of catalytic reactions:

Heterogenous and Homogeneous.

In a heterogeneous reaction, the catalyst is in a different phase from the reactants.

In a homogeneous reaction, the catalyst is in the same phase as the reactants.