unlike Cr3+, Mn2+, Fe3+ and other subsequent M2+ ions of the 3d series of elements , the 4d and 5d series metals generally do not form stable cationic species.

Dear Mohini,

• The transition elements are group of industrially important metals mainly due to their strong inter-atomic metallic bonding giving them generally high melting/boiling points and high tensile strength.

• These-called transition metal characteristics arise from an incomplete d sub-shell energy level but scandium and zinc are not true transition metals i.e. Ti to Cu are the real transition elements (reasoning later).

• Note that physically, zinc is low melting and a lower tensile strength compared to the others in the 3d block.

• Although scandium is physically typical of a transition metal e.g. high melting point and high tensile strength, chemically, scandium only forms a single and colourless triple charged ion (Sc³⁺). Therefore like zinc (only Zn²⁺), shows non of the typical characteristics of transition metal chemistry e.g. variable oxidation state, coloured complex ions, catalytic properties of the metal or ion. This is all explained in detail later.

• Therefore probably the best definition of a transition metal is an element which forms at least one ion with an incomplete d sub-shell containing at least one electron. How this relates to variable oxidation state and coloured complex ions is elaborated further in section 10.2 and the subsequent sections on the individual metals (links below) and some of the. Zinc (Zn²⁺, [Ar]3d¹⁰) and scandium (Sc³⁺, [Ar]3d⁰) cannot meet this criteria.

• The presence of the partially-filled d sub-shells of electrons gives transition elements properties which are not in general possessed by the main group elements, namely Groups 1-7 and 0, BUT, there are similarities with other metals, particularly in Groups 2, 3 and  4.

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