Transition metal

In chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings:

Electronic configuration

Main group elements prior to the appearance of the transition group elements in the periodic chart (ie, elements number 1 through 20) have no electrons in d orbitals, but only in the s and p orbitals.

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The 3rd period p block elements have empty d orbitals. In the fourth period from scandium to zinc, d-block elements fill up their d orbitals across the period. With the exception of the copper group and the chromium group, all d-block elements in the ground state have two electrons in their outer s orbital. The electronic configuration of the d-block elements is ns2(n?1)d1-10, where n is the ground state principal quantum number.

Related Topics:
Scandium - Zinc - Copper - Chromium - Ground state - Electron - Principal quantum number

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The outer s orbitals in the d-block elements are at lower energy states than the d orbitals of the n?1 levels. As atoms always strive to be in states of lowest energy, s orbitals are filled up first. The copper (4s13d10) and chromium (4s13d5) exceptions, which have one electron in their outer orbital, occur because half- and fully-filled orbitals are more stable than any other configurations (this occurs when there are 5 or 10 electrons in the d-orbitals).

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Scandium has one electron in its d orbital, and 2 electrons in its outer s orbital. As scandium's only ion (Sc3+) has no electrons in its d orbital it is clear that it does not have a 'partially filled d orbital', and is not a transition metal in the stricter sense. Similarly, zinc is not a transition metal in the stricter sense because its only ion, Zn2+, has a full d orbital, which does not participate in bonding.

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