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Transition Metals

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The transition elements form three series of metals that progress from elements that give up or lose electrons to elements that gain or accept electrons. The elements that are in transition from metals to non metals are located in the center of the periodic table in periods 4, 5 and 6 and are found in groups 3 through 12.


The transition elements or transition metals are elements whose atom has an incomplete d sub shell or which can give rise to cations with an incomplete d sub shell. Transition elements may be defined as the element whose atoms or simple ions contain partially filled d-orbitals.

Transition Metals Definition

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What is Transition Element?

"The transition metals are defined as those elements which have partly filled d or f shells either in the elemental state or their compounds. The transition metals react with a Variety of groups or molecules called ligands (L) to yield transition metal complexes."

The first transition series involves the filling of 3d orbitals, second 4d orbitals, third 5d orbitals. The general electronic configuration of transition elements is (n-1)d1-10ns1-2. The transition metals are also unique in their outermost valence shell is not the main energy level being completed by sharing electrons. The transition metals are unique in representing a gradual shift in electronegativity. Electronegativity is characterized by the neutral atom ability to acquire electrons from outside itself and thus neutral atoms have a tendency to become negatively charged.

Transition Metals on the Periodic Table

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The transition element family is found in the middle of the periodic table in Groups 3-12. The transition element family is the largest family on the periodic table with 40 members. The transition elements are all metals tats why they are sometimes called the transition metals.

  1. Most of the elements in this family are hard, strong and shiny metals.
  2. Most of them have very high melting points and boiling points.
  3. Mercury is one exception it is a liquid at room temperature.
  4. Most transition elements are good conductors of heat and electricity.
  5. Most transition elements will dissolve in acid. Gold is one exception it resists acids.
Transition Metals on the Periodic Table

The transition metals change gradually as one moves from left to right across the bridge. On the left side of the bridge the elements have only a few electrons moving through their valence shell.

Transition Metals List

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The list of transition metals are given below.


Period 4 after [Ar] Period 5 after [Kr] Period 6 after [Xe] Period 7 after [Rn]
3 Scandium 21 4s2 3d1 Yttrium 39
5s2 4d1
Lutetium 71 6s2 4f14 5d1 Lawrencium 103
7s2 4f14 7p1
4 Titanium 22 4s2 3d2 Zirconium 40 5s2 4d2 Hafnium 72 6s2 4f14 5d2 Rutherfordium 104 7s2 4f14 6d2
5 Vanadium 23 4s2 3d3 Niobium 41 5s1 4d4 Tantalum 73 6s2 4f14 5d3 Dubnium 105 (unknown)
6 Chromium 24 4s1 3d5 Molybdenum 42 5s1 4d5 Tungsten 74
6s2 4f14 5d4 Seaborgium 106 (unknown)
7 Manganese 25 4s2 3d5 Technetium 43 5s2 4d5 Rhenium 75 6s2 4f14 5d5 Bohrium 107 (unknown)
8 Iron 26 4s2 3d6 Ruthenium 44 5s1 4d7 Osmium 76 6s2 4f14 5d6 Hassium 108 (unknown)
9 Cobalt 27 4s2 3d7 Rhodium 45 5s1 4d8 Iridium 77 6s2 4f14 5d7 Meitnerium 109 (unknown)
10 Nickel 28 4s2 3d8
or
4s1 3d9

Palladium 46 4d10 Platinum 78
6s1 4f14 5d9 Darmstadtium 110 (unknown)
11
Copper 29 4s1 3d10 Silver 47 5s14d10 Gold 79 6s1 4f14 5d10 Roentgenium 111 (unknown)
12 Zinc 30 4s2 3d10 Cadmium 48 5s2 4d10 Mercury 80 6s2 4f14 5d10 Copernicium 112 (unknown)

Post Transition Metals

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The post transition metals are those metals that occur in the periodic table immediately following a row of transition metals. The two most common and important ones are tin (Sn) and lead (Pb). Except for bismuth post transition metals have the ability to form two different ions and therefore two different compounds with a given non metal.

"The transition metals in the last row are not found in nature but have been synthesized artificially. The metals that follow the transition metals are called post transition metals."
Metallic elements from periods 4-6 in groups following the transition series are post transition metals. They are less electropositive than the pre transition metals and are typically found in nature as sulfides rather than silicates. They form compounds with oxidation states corresponding to d10 ions where s and p electrons have been ionized but these are less ionic in character than corresponding compounds of pre transition metals. In solution post transition metals form the stronger complexes than with pre transition metals.

Transition Metal Charges

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  1. Transition metals form cations but can lose varying numbers of electrons thus forming ions of different charges.
  2. Therefore the group number is not an accurate guide to charges. It is important to learn which ions are forms most frequently by these metals.
  3. Many transition metals form +2 and +3 ions. For example, iron atoms can lose two or three electrons to form Fe2+ or Fe3+ respectively.

Transition Metal Complexes

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Color of Transition Metals

The characteristic color of many transition metal complexes MLn arise either from d-d* transitions at a metal center or from charge transfer transitions between a metal center M and the ligands L.

Some examples of complexes where the color arises from d-d* transition are [Cr(H2O)6]3+ (violet) and [Co(NH3)6]3+ (gold brown). There are two types of charge transfer process. In the first case the electron is transferred from the ligand to the metal, the transfer produces metal reduction bands in the UV spectrum. The second type of CT processes is electron migration from metal to ligand which leads to metal oxidation bands in the UV region.

Electron Configuration of Transition Metals

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The transition metal electron configuration are given below.

Group number 4
5
6
7
8
9
10
11
First row 3d
Ti V
Cr
Mn
Fe Co
Ni
Cu
Second row
4d
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Third row
5d
Hf
Ta
WReOs
Ir
Pt
Au
Oxidation states 0 4 5
6
7
8
9
10
--
I
3
4
5
6
7
8
9
10
II
2 3
4
5
6
7
8
9
III
1
2
3
4
5
6
7
8
IV 0
1
2
3
4
5
6
7

The transition series is formed by the systematic filling of the d orbitals. Note that these electron configurations differ from those presented in most elementary texts in which the 4s level is presumed to be lower in energy than the 3d and is filled first.

Oxidation States of Transition Metals

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The transition metals exhibit variety of oxidation states. The oxidation states of transition elements are due to the participation of ns and (n-1) d electrons in bonding. The lower oxidation state is generally exhibited when ns electrons participate in bonding and higher oxidation states are shown when ns as well as (n-1) d-electrons take part in bonding.

It may be noted the oxidation states of transition elements differ from each other by unity whereas oxidation states of non transition elements generally differs by two. The highest oxidation state shown by any transition metal is +8 and the lower oxidation state is generally +2 and +3. Some transition metals also show oxidation state of zero in their compounds.

Characteristics of Transition Metals

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The general characteristics of transition metals are
  1. Transition elements are metals.
  2. They exhibit variable valency or oxidation state.
  3. They are less reactive than s-block and p-block elements.
  4. They generally form colored compounds except those compounds in which the metal ion have either d0 or d10 electrons.
  5. Transition metals and their compounds have marked catalytic activity.
  6. They form complex compounds.
  7. They are generally paramagnetic that is attract magnetic lines of forces. This property is due to presence of unpaired electrons in d-sub shell. On account of absence of unpaired electron they are diamagnetic.

Uses of Transition Metals

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The examples of transition metals and their uses are tabulated below.

S.No
Metals
Examples of uses
1
Scandium
Alloys with aluminum
2
Titanium
Space and aircraft vehicles, replacement hi joints.
3
Vanadium
Alloys with iron to make hard steels.
4
Chromium
Alloys with iron to make stainless steel for cutter.
5 Manganese
Alloys with iron for making springs, paper clips.
6
Iron Making steels for cars, machines, construction girders.
7
Cobalt Alloys with iron to make hard steel.
8
Nickel Alloys with copper to make coinage metals.
9
Copper
Electrical and plumbing work making the alloys brass and bronze coins.
10
Zinc Coating for iron (galvanizing) alloys with copper to make brass.

Properties of Transition Metals

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The transition metals all have two electrons in the outer shell, but they differ in the number of electrons in the penultimate shell. They have similar properties because the chemical properties of an element are mainly due to the number of electrons in the outer shell. The properties show a gradual change or transition across the series.
  1. They are all metals and have high melting points and boiling points. Car engines for example, are made from iron because it can withstand temperatures over 1000oC without melting.
  2. They are good conductors of heat and electricity. The wiring in houses and the central heating pipes are made of copper because it is a good conductor of electricity and heat.
  3. They are strong so are used to build bridges the frames of buildings vehicles and machines.
  4. Most have a high density. Titanium has a lower density than most transition metals, so it is used to make modern aircraft because it is also strong and can withstand high temperatures.
  5. They form colored compounds. The compounds of most of the other elements in the periodic table are white
The atoms or molecules or ions which donate pair of electrons to the central metal atom and thus forms coordinate bond with the central metal atom.
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Chelating Ligand

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Chelating ligands must therefore have at least two ligating atoms. The total number of ligand atoms that can bind simultaneously to one metal center is the density of the ligand. A closed loop containing the metallic coordination center is called chelate ring.
A Complex ion may be defined as an electrically charged radical or species carrying positive or negative charge in which central metal ion is surrounded by a fixed number of group of ions or neutral molecules.
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Dissociation constant is a specific type of equilibrium constant that measures the propensity of a larger object to separate reversibly into smaller components as when a complex falls apart into its component molecules or when a salt splits up into its components ions.
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Binding affinity is defined by the Gibbs energy of binding which in turn is determined by the enthalpy and the entropy changes.
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The redox potential is a valuable tool in many chemical endeavors it can be used to follow the progress of chemical reactions and to determine endpoints of titrations; the redox principle has many industrial applications corrosion of metals is governed by oxidation reduction reactions.
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Ligands which have more than one atom with a lone pair that can be used to bond to a metal ion. Such ligands are said to be chelating ligands or chelates. A ligand that can form two bonds to a metal ion is called a bidentate ligand.
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