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Transition Metal Transition Metal In chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings: The IUPAC definition states that 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". Most scientists describe a "transition metal" as any element in the d-block of the periodic table, which includes groups 3 to 12 on the periodic table. All elements in the d-block are metals. In actual practice, the f-block is also included in the form of the lanthanide and actinide series.

Transition Metals Definition The elements belonging to 3 to 12 group, present in the center of the periodic table are called as 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.

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The transition metals are unique among the chemical elements. The elements in which 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 dblock 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.)

Characteristics of Transition Metals 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 behaviors. These metals and their compounds also exhibit catalytic properties. Some of the important properties of transition metals are

1. Electronic Configuration The electronic configurations 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.

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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.

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