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  Transition Elements Homework Help - K-12 Grade Level, College Level Chemistry

Introduction to Transition Elements

The term transition element (sometimes also known as transition metal) has two probable meaning in chemistry,:

 IUPAC (i.e. International Union of Pure and Applied Chemistry) definition explains that a transition element is "an element whose atom has an partially filled d sub-shell, or which can give cations with an incomplete d sub-shell".

Most scientists explains a "transition element" as any element in the d-block of the periodic table, which contains groups from 3 to 12 in the periodic table. All of the elements in d-block are elements. In real practice f-block is also incorporated in the form of lanthanide and actinide series.

Jensen has evaluated the history of the terms transition element and the d-block. The word transition was initially used to explain the elements now called as the d-block in 1921 by the English chemist Charles Bury, who referred to a transition series of the elements at the time of change of an inner layer of electrons (for instance n=3 in the 4th row of the periodic table) form a stable group of 8 to one of the 18, or from 18 to 32.

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Characteristic properties

There are various properties followed by the transition elements that are not exist in other elements, which results from partly filled the d- shell. These involve

  • The formation of compounds whose colour is because of d - d electronic transitions
  • The formation of the compounds in various oxidation states, due to the comparatively low reactivity of unpaired d -electrons.
  • The formation of various paramagnetic compounds because of presence of unpaired d electrons. Some compounds of main group elements are paramagnetic too (e.g. nitric oxide, oxygen)

Classification

The elements of groups 4-11 are now usually identified as transition metals just as Sc and Y in Group 3. For the elements like La-Lu and Ac-Lr and for Group 12 also, several sets of definitions are utilized by various authors.

1.      Various chemistry textbooks and printed periodic tables categorize La and Ac as Group 3 elements and transition metals, however their atomic ground-state configurations are s2d1 as Sc and Y. The elements Ce-Lu are taken as "lanthanide" series (or "lanthanoid" as per IUPAC) and Th-Lr as the "actinide" series. The 2 series together are categorized as f-block elements, as "inner transition elements".

2.      Few inorganic chemistry textbooks involve La with the lanthanides and Ac with the actinides. This classification is on the basis of similarities in chemical behaviour and explains 15 elements in each of the two series even though they correspond to the filling of an f subshell which can only include 14 electrons.

3.      A third categorization explains the f-block elements as La-Yb and Ac-No while placing Lu and Lr in Group 3. This is on the basis of aufbau principle (or Madelung rule) for filling electron subshells, in which 4f is filled previous to 5d (and 5f before 6d), so that f subshell is really full at Yb (and No) whereas Lu (and Lr) has an [ ]s2f14d1 configuration. Though La and Ac are exceptions to Aufbau principle with electron configuration [ ]s2d1 (not [ ]s2f1 as the aufbau principle says) so it is not apparent from atomic electron configurations whether La or Lu (Ac or Lr) must be taken as a transition metal.

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