Structure and characteristics of key transition metals

By the lUPAC (International Union of Pure and Applied Chemistry) definition, a transition metal is an element, an atom of which contains an incomplete d shell, or that gives rise to a cation with an incomplete d shell. Transition metals have a total of nine atomic orhitals, but only some of these are used for bonding to ligands. Coordination number denotes the number of donor atoms associated with the central atom and dictates the shape, or stereochemistry, of the coordination complex. The most common coordination numbers for the first transition metal series are four (tetrahedral and square-planar) and six (octahedral). Metals in the early second and third series are larger and thus can have higher coordination numbers, forming more stmcturally complex molecules. 

The electronic structure of transition metals in their ground state and oxidation states often causes considerable confusion. As electrons are negatively charged particles, removal of electrons makes the metal more positive (hence -h sign), and conversely when electrons are added to a metal it becomes more negative (hence-sign). When considering metals and electrons there are three important terms to remember  

Oxidation This describes the process by which electrons are removed from the metal (M), where the metal has been oxidized. Notably solutions containing Fe(II) tend to oxidize to the Fe(III) ion. 

Oxidation state This refers to the number of electrons that have been added to or subtracted from the metal. It is often given in brackets, and where one electron is removed from M, the oxidation state is - -1 (or +), denoted as M(I), whereas addition of two electrons to M places it in the —2 (or 2 ) oxidation state, denoted as M(—II). 

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To describe and explain the structure and characteristics of key transition metals. 

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