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Transition Metals

What are Transition Metals?

Transition metals or transition elements on the periodic table are the d-block chemical elements lying between p-and s-block elements. These elements either in their atomic state or in any of their common oxidation number or state have partially filled (n-1)d orbital. The valence shell electronic configuration of d-block elements or transition metals, (n−1)d^{1 to 10} ns^{0, 1, 2}. The f-block elements (lanthanides or rare-earth elements and actinides) in the periodic table are called inner transition metals.

Transition metals or d-block elements in periodic table with names, symbols, atomic number and electronic configuration

The f block elements are named inner transition metals because the additional electron enters into (n−2)f orbitals.

Transition Metals on the Periodic Table

According to the definition of transition metal, copper, silver, and gold should be excluded from d-block elements on the periodic table. Since these elements do not have partially filled d-orbitals in their atomic or common oxidation state.

Similarly, zinc, cadmium, mercury, and palladium do not contain partially filled d-orbital in their atomic or common +2 oxidation state.

Due to similar properties and to maintain a rational classification, these elements are generally studied with d-block or transition metals.

Electronic Configuration of Transition Elements

All the transition elements or d-block elements are classified into four series such as 3d, 4d, 5d, and 6d. Each 3d, 4d, 5d, and 6d series has ten chemical elements.

The general valence shell electronic configuration of transition elements,
(n-1)d^{1 to 10} ns^{0, 1, 2}

First Transition Series

**Electronic configuration of the first transition series**
Transition element	Symbol	Atomic number	Electronic configuration
Scandium	Sc	21	[Ar] 3d¹ 4s²
Titanium	Ti	22	[Ar] 3d² 4s²
Vanadium	V	23	[Ar] 3d³ 4s²
Chromium	Cr	24	[Ar] 3d⁵ 4s¹
Manganese	Mn	25	[Ar] 3d⁵ 4s²
Iron	Fe	26	[Ar] 3d⁶ 4s²
Cobalt	Co	27	[Ar] 3d⁷ 4s²
Nickel	Ni	28	[Ar] 3d⁸ 4s²
Copper	Cu	29	[Ar] 3d¹⁰ 4s¹
Zinc	Zn	30	[Ar] 3d¹⁰ 4s²

Second Transition Series

**Electronic configuration of second transition series**
Transition element	Symbol	Atomic number	Electronic configuration
Yttrium	Y	39	[Kr] 4d¹ 5s²
Zerconium	Zr	40	[Kr] 4d² 5s²
Niobium	Nb	41	[Kr] 4d⁴ 5s¹
Molybdenum	Mo	42	[Kr] 4d⁵ 5s¹
Technetium	Tc	43	[Kr] 4d⁵ 5s²
Ruthenium	Ru	44	[Kr] 3d⁷ 5s¹
Rhodium	Rh	45	[Kr] 3d⁷ 4s²
Palladium	Pd	46	[Kr] 4d¹⁰ 5s⁰
Silver	Ag	47	[Kr] 4d¹⁰ 5s¹
Cadmium	Cd	48	[Kr] 4d¹⁰ 5s²

Third Transition Series

**Electronic configuration of the third transition series**
Transition element	Symbol	Atomic number	Electronic configuration
Lanthanum	La	57	[Xe] 4f⁰ 5d¹ 6s²
Hafnium	Hf	72	[Xe] 4f¹⁴ 5d² 6s²
Tantalum	Ta	73	[Xe] 4f¹⁴ 5d³ 6s²
Tungsten	W	74	[Xe] 4f¹⁴ 5d⁴ 6s²
Rhenium	Re	75	[Xe] 4f¹⁴ 5d⁵ 6s²
Osmium	Os	76	[Xe] 4f¹⁴ 5d⁶ 6s²
Iridium	Ir	77	[Xe] 4f¹⁴ 5d⁷ 6s²
Platinum	Pt	78	[Xe] 4f¹⁴ 5d⁹ 6s¹
Gold	Au	79	[Xe] 4f¹⁴ 5d¹⁰ 6s¹
Mercury	Hg	80	[Xe] 4f¹⁴ 5d¹⁰ 6s²

Fourth Transition Series

**Electronic configuration of the fourth transition series**
Transition element	Symbol	Atomic number	Electronic configuration
Actinium	Ac	89	[Rn] 5f⁰ 6d¹ 7s²
Rutherfordium	Rf	104	[Rn] 5f¹⁴ 6d² 7s²
Dubnium	Db	105	[Rn] 5f¹⁴ 6d³ 7s²
Seaborgium	Sg	106	[Rn] 5f¹⁴ 6d⁴ 7s²
Bohrium	Bh	107	[Rn] 5f¹⁴ 6d⁵ 7s²
Hassium	Hs	108	[Rn] 5f¹⁴ 6d⁶ 7s²
Meitnerium	Mt	109	[Rn] 5f¹⁴ 6d⁷ 7s²
Darmstadtium	Ds	110	[Rn] 5f¹⁴ 6d⁸ 7s²
Roentgenium	Rg	111	[Rn] 5f¹⁴ 6d⁹ 7s²
Copernicium	Cn	112	[Rn] 5f¹⁴ 6d¹⁰ 7s²

Properties of Transition Elements

The properties of transition elements of a given period are not so much different from one another. The reason for this fact lies in the electronic configuration of transition elements.

The general electronic configuration of transition metals differs one from another only in the number of electrons in the d-orbital. The number of electrons in the outermost shell is invariably 0, 1, or 2.

Metallic Character of Transition Elements

All the transition elements are metals due to their small number of electrons in the outermost quantum shell. They are hard, malleable, and ductile. They have formed all four types of crystalline solids − face-centered cubic, hexagonal closed packed, body-centered cubic, and face-centered cubic crystal lattice.

Metallic and covalent bonding both exist in atoms of transition metals. Due to the presence of incomplete d-orbital, most of the transition metals combine with other elements by covalent chemical bonding. These metals are good conductors of heat and electricity.

Transition Metals Melting Point Trends

The transition elements have very high melting and boiling points compared to s- and p-block elements.

The metals zinc, cadmium, and mercury have relatively low values due to completely filled d-orbitals. No unpaired electrons are available for covalent bonding among the atoms of zinc, cadmium, and mercury.

The other transition metal contains an incompletely filled d-orbital for covalent bonding.

Atomic and Ionic Radii of Transition Elements

The atomic and ionic radii decrease generally on moving from left to right in the period. This is due to the fact that an increase in nuclear charge tends to attract the electron clouds towards the nucleus of an atom.

The atomic radii of chromium to copper are very close to one another. Due to the simultaneous addition of shielding electron to 3d-level reverse effect on outer 4s-electrons. The ionic radii of M⁺² and M⁺³ ions follow the same trends as atomic radii.

Ionization Energy of Transition Metals

The first ionization energy of transition metals lies between the values of s- and p-block elements. The first ionization energy values lie between 5 to 10 electron volts.

In the case of transition metals, the addition of extra shielding electron shields or decreases the inward pulls of the positive nucleus and ns electrons. The effects of the increasing nuclear charge and shielding effects oppose each other.

On account of these counter effects, the ionization potentials increase slowly on moving in a period of the first transition series.

From the above picture, it is clearly indicated that the first ionization energies of Ti, V, and Cr differ slightly from one another. Similarly, the values of Fe, Co, Ni, and Cu are fairly close to one another.
Second ionization energy is seen to increase more or less regularly with the increasing atomic number of d-block or transition elements. The values of second ionization energy chromium and copper are higher than that of their neighbor transition metals due to the extra stability of Cu⁺ and Cr⁺ ions.

Oxidation Number of Transition Metals

One of the most important properties that distinguish transition metals from non-transition elements is variable oxidation numbers or states.

This unique property is due to the fact that the energy levels of 3d, 4d, and 5d orbitals are close to the 4s, 5s, and 6s orbitals respectively. Therefore, in addition to ns electrons, the various numbers of (n−1)d electrons are also lost to show various oxidation states.

Catalytic Activity of Transition Metals

Most of the transition metals and their compounds are used as good chemical catalyst in different types of reactions. Some examples are

Vanadium pentoxide (V₂O₅) is used in the manufacture of sulfuric acid in the contact process.
Finely divided powdered nickel or active nickel is used in hydrogenation reactions of organic compounds.
Spongy platinum is used in the conversion of sulfur dioxide to sulfur trioxide or the production of nitric acid by the Ostwald process.
Transition metal, iron is used in the manufacture of ammonia by the Haber process.