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Inner Transition Metals

Periodic table a tabular form to arrange all elements exist in nature. Out of all elements more than 75% elements are metal in nature and positioned at the left side of the table. All nonmetals arranged at the right side of the table, are very different from metals. Metal and non-metals are separated by certain elements known as metalloid which show intermediate properties.

Today we have a large number of elements which cannot study only on the basis of their metallic and non-metallic nature. That classification was enough for few elements but cannot be used for all the known elements. Therefore today we are using the long form of the periodic table which is based on the atomic number of elements. The elements are arranged in table with 18 groups, vertical columns and 7 periods, horizontal rows.

On the basis of valence shell electronic configuration of elements, they can be divided into s, p, d and f-blocks. The main table of periodic table has s, p and d-block. The f-block elements are placed at the bottom of the main table in 2 series of 14 elements. The d-block elements are also known as transition elements because they can show variable oxidation states. For example, Mn can show oxidation states from +2 to +7. These elements have fulfilled valence shell but the penultimate shell is incomplete. Similarly, f-block elements are better known as inner transition elements. In these elements, the valence electrons are filled in ultimate orbital, not in the penultimate and valence shell. Therefore these elements are called as inner transition elements.

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Transition Metals Definition

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The elements belonging to 3 to 12 group, present in the center of the periodic table are called transition metals. These are actually d- block metals and form a bridge in between the s and p block elements, the metals and non metals. The transition metals are unique among the chemical elements. The elements in which the last electron enters the d- sub shell of their penultimate shell (n-1 shell) are known as d- block elements.
Thus, transition metals can be broadly defined as those which either as elements or as ions have partially filled d-subshell. Since d-subshell is partially filled, the elements are called as d- block elements.
The transition metals are classified into four transition series. Each series (Except 6d) consists of 10 elements. (This is because the d- sub-shell can occupy only 10 electrons and they get filled up when we move along a period in a series.)

First Transition Series

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It is a part of the fourth period and consists of 10 elements from Scandium (At no: 21) to zinc (at no 30) in which 3d - sub-shells are progressively filled.This is also called as 3d series which corresponds to the filling of the 3d orbital.

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

Second Transition Series

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Second transition series is a part of the fifth period and consists of 10 elements from Yttrium (At no: 39) to cadmium (At no: 48) in which 4d- sub-shells are being progressively filled. This is also called 4d series which corresponds to the filling of the 4d orbital.

Element Atomic Number Symbol Electronic configuration
39 Y [Kr] 4d1 5s2
Zirconium 40 Zr [Kr] 4d2 5s2
Niobium 41 Nb [Kr] 4d4 5s1
Molybdenum 42 Mo [Kr] 4d5 5s1
Technetium 43 Tc [Kr] 4d5 5s2
Ruthenium 44 Ru [Kr] 4d7 5s1
Rhodium 45 Rh [Kr] 4d8 5s1
Palladium 46 Pd [Kr] 4d10 5s0
Silver 46 Ag [Kr] 4d10 5s1
Cadmium 48 Cd [Kr] 4d10 5s2

Third Transition Series

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It is a part of the sixth period and consists of 10 elements from Lanthanum (At no: 57) and Hafnium (At no: 72) to Mercury (At no: 80) in which the 5d sub-shell is progressively filled. This is also called as 5d series which corresponds with the filling of 5d orbital.

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

Fourth Transition Series

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It is a part of the seventh period and is an incomplete series starting from actinium (At no: 80) in which 6d sub-shell is being progressively filled.This is also called as 6d series which corresponds with the filling of 6d orbitals. This series contains only 3 elements. They are actinium with atomic number 89 followed by two elements with atomic numbers 104 and 105.

Element Atomic No Symbol Electronic configuration
Actinium 89 Ac [Rn] 6d1 7s2

Transition metal charges

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The valence electrons of transition metals are responsible for the charges that these metals carry or show and has been explained below.The valence or the electrons in the ultimate shell enter the 'd' orbital. The first element in each series stats with one valence electron or 'd' electron and the last element will have 10 'd' electrons.Variable oxidation state or variable valency is one of the most striking features of the transition elements. All transition elements, except the first and last member of each series exhibit variable valency, related to its electronic structure. These elements lose both the 's' an the 'd' electrons and thus have a lot of valencies. Consequently, all transition elements in general exhibit variable valencies.Valencies of first transition series are

Oxidation state/valency
Sc +2, +3
Ti +2, +3, +4
V +2, +3, +4, +5
Cr +1 to +6 (+4 and +5 are unstable)
Mn +2 to +6(+4, +5 and +6 are unstable)
Fe +2 to +6 (+4, +5 and +6 are unstable)
Co +2 to +6 (+4 is unstable)
Ni +2, +3, +4
Cu +1, +2
Zn +2

Characteristics of Transition Metals

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The transition metals properties are described as follows.

Transition elements have partly filled d- orbitals. These elements show several interesting properties like variable oxidation state or variable valency, formation of colored complexes and paramagnetic behavior. These metals and their compounds also exhibit catalytic properties.

Some of the important properties of transition metals are

1. Electronic Configuration

The electronic configuration of transition elements may in general be represented as
(n-1) d 1-10 ns1 or 2

The (n-1) means penultimate or next to the outermost shell and d- orbital may have 1 to 10 electrons and the s- orbital of the outermost shell (n) may have 1 or 2 electrons. The electronic configurations of all the four series of elements are given in a table above.

2. Atomic and ionic radii

The atomic and ionic radii of the elements of a particular transition series decreases from left to right. In the first series, the atomic radii become almost constant for chromium, because of two factors-Increase in nuclear charge and increase in the screening effect which just balance each other.

Atomic radii of Chromium is - 117pm. Mn, the next element has an atomic radii of 117 pm. The next three elements, Co, Ni and Cu has 116. 115 and 117 respectively.
To summarize, atomic and ionic radii decrease with increase in atomic number, due to increase in nuclear charge.

3. Magnetic Properties

Magnetic character is of two types.
  • Paramagnetic
  • Diamagnetic
Those which are attracted by the magnetic field are termed as paramagnetic and those repelled by the magnetic field are diamagnetic. Transition elements and their compounds are paramagnetic in nature, they conduct electricity.

Paramagnetism is due to the presence of unpaired electrons in the d- orbitals of the transition metal atoms, ions or molecules. The greater the number of unpaired electrons, the greater will be its magnetic behavior. So, all transition metals with at least one unpaired electron are paramagnetic.

4. Color

Most d- block compounds are colored in the solid or in solution states. The color of the transition metal ions is due to the presence of unpaired or incomplete (n-1) d orbitals and the ability to promote an electron from one energy level to another. In these ions d- electrons are promoted to the higher energy levels within the same d- sub-shell. The color exhibited depends upon the complementary color of light observed by these ions.

Colors of some transition metals are

Color observed
Fe2+ Green
Ni2+ Green
Cu2+ Blue
Fe3+ Yellow
Mn2+ Pink

5. Complex formation

Complex formation or complexation is a typical behavior of transition metals. In these complex compounds, the transition metal ions form co-ordinate bonds with a number of neutral or negatively charged ions which are capable of donating electrons to the metal atom.

A few examples are [Fe(CN)6]3-, [Fe(CN)6]4-, [Cu(NH3)4]2+, etc.

6. Catalytic behavior

Most of the transition elements and their compounds are good catalysts. Platinum, cobalt, nickel, chromium, manganese, vanadium pent-oxide, etc are good examples. They are used as catalysts since they have incomplete d- orbitals and can form unstable intermediates which can then change into products.

Transition Metals

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Inner transition elements are also called as f- block elements. The elements in these group are present below the main table and contains two series.
  1. The first series is called as Lanthanoid series and starts from Cerium (Ce atomic number -58) to Lutetium (Lu atomic number- 71). There are totally 14 elements in this series.
  2. The second series is called the actinoid series. This series also contains 14 elements from Thorium (Th - 90) to Lawrencium (Lr- 103).
Most of the actinoids are radioactive isotopes, and do not occur in nature. They are the result of a radioactive decay and thus are not stable.

More topics in Inner Transition Metals
Metallurgy Transition Elements
D-block Elements F block Elements
Photochemical Reaction Lanthanides and Actinides
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