Download The d-block elements are commonly known as transition

The d-block elements are commonly known as transition metals or
transition elements.
LEARNING OBJECTIVES [ edit ]
Identify the transition metal atoms on the periodic table.
Identify the distinctive and characteristic properties of the transition metals.
KEY POINTS [ edit ]
Transition metals are elements in the ten middle groups of the fourth, fifth, sixth, and
seventh periods of the periodic table.
Transition metals and their compounds can exhibit color due to internal d-d electron transfers.
Transition metals and their compounds can exhibitferromagnetism, paramagnetism, and
diamagnetism.
Transition metals and their compounds are well known for their catalytic activities.
TERMS [ edit ]
Oxidation State
The state of an atom having a particular oxidation number.
paramagnetic
Exhibiting paramagnetism; the tendency of magnetic dipoles to align with an external magnetic
field.
diamagnetic
Exhibiting diamagnetism; repelled by a magnet.
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The d-Block of the Periodic Table
The transition metals are also known as thetransition elements or the d-block elements. As
the name implies, the chemistry of this group is determined by the extent to which the delectron suborbital levels are filled. Chemical similarities and periodicities can be easily seen
horizontally across the d-block of the periodic table.
The d-block of the periodic table
The d­block is composed of groups 3 ­ 12 and periods 4 ­ 7.
The chemistry is far from simple, however, and there are many exceptions to the orderly
filling of the electron shell. The Aufbau principle provides an methodical framework for
predicting the order in which most atoms will populate their electron shells.
The Aufbau principle
This illustrates the order in which most atoms populate their electron shells.
Chemical properties in the periodic table are organized vertically, by group, for similar
chemical and physical properties. For example, the metals in group 11 have similar
characteristics of electrical conductivity, luster, crystal structure, ductility, and tensile
strength. Moving horizontally across the periodic table trends in properties such as atomic
radius, electronegativity, and electron affinity are observed.
Characteristic Properties of Transition Metals
Transition metals can be said to possess the following characteristics generally not found in
the main grouping of the periodic table. They can be mostly attributed to incomplete filling of
the electron d-levels:
The formation of compounds whose color is due to d–delectronic transitions.
The formation of compounds in many oxidation states due to the relatively
low reactivity of unpaired d electrons.
The formation of many paramagnetic compounds due to the presence of
unpaired d electrons. A few compounds of main group elements are also paramagnetic
(e.g., nitric oxide, oxygen).
Ligand-to-Metal Charge-Transfer (LMCT) Transition
Color in transition-series metal compounds is generally due to the electronic transitions of
two principal types of charge transfer transitions. An electron may jump from a
predominantly ligand orbital to a predominantly metal orbital, giving rise to a ligand-tometal charge transfer (LMCT) transition. These can most easily occur when the metal is in a
high oxidation state. For example, the color of chromate, dichromate, and
permanganate ions is due to LMCT transitions. Another example is that mercuric iodide
(HgI2) is red because of a LMCT transition.
Charge-transfer complexes
I2•PPh3 charge­transfer complexes in CH2Cl2. From left to right: (1) I2dissolved in dichloromethane—no
CT complex. (2) A few seconds after excess PPh3 was added—CT complex is forming. (3) One minute later
after excess PPh3 was added—the CT complex [Ph3PI]+I­has been formed. (4) Immediately after excess
I2 was added, which contains [Ph3PI]+[I3]­.
A metal-to-ligand charge transfer (MLCT) transition will be most likely when the metal is in a
low oxidation state and the ligand is an easily reduced d-d transition. An electron jumps from
one d-orbital to another. In complexes of the transition metals, the d orbitals do not all have
the same energy.
Paramagnetic and Diamagnetic Compounds
Transition metal compounds are paramagnetic when they have one or more
unpaired d electrons. Some compounds are diamagnetic. These include octahedral, lowspin, d6 and square-planar d8complexes. In these cases, crystal field splitting is such that all
the electrons are paired up. Ferromagnetism occurs when individual atoms are paramagnetic
and the spin vectors are aligned parallel to each other in a crystalline material. Metallic iron
and the alloy alnico are examples of ferromagneticmaterials involving transition metals. Antiferromagnetism is another example of a magnetic property arising from a particular
alignment of individual spins in the solid state.
The transition metals and their compounds are known for their homogeneous
and heterogeneous catalytic activity. This activity is attributed to their ability to adopt
multiple oxidation states and to form complexes.