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The recent discovery that mercury can use its d

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not ordinarily involved in chemical bonding. The recent discovery that mercury can use its d electrons in the formation of mercury(IV) fluoride (HgF 4 ) has prompted some commentators to suggest that mercury can be regarded as a transition metal. [109] Other commentators, such as Jensen, [110] have argued that the formation of a compound like HgF 4 can occur only under highly abnormal conditions. As such, mercury could not be regarded as a transition metal by any reasonable interpretation of the ordinary meaning of the term. [110] Still other chemists further exclude the group 3 elements from the definition of a transition metal. They do so on the basis that the group 3 elements do not form any ions having a partially occupied d shell and do not therefore exhibit any properties characteristic of transition metal chemistry. [111] In this case, only groups 4–11 are regarded as transition metals. Period 6 and 7 elements in group 3 Although scandium and yttrium are always the first two group 3 elements, the identity of the next two elements is not agreed upon; they are either lanthanum and actinium, or lutetium and lawrencium. Although there are some strong physical and chemical arguments supporting the latter arrangement not all authors are convinced. [112]
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6/2/13 11:44 AM Periodic table - Wikipedia, the free encyclopedia Page 13 of 17 http://en.wikipedia.org/wiki/Periodic_table Optimal form The many different forms of periodic table have prompted the question of whether there is an optimal or definitive form of periodic table. The answer to this question is thought to depend on whether the chemical periodicity seen to occur among the elements has an underlying truth, effectively hard-wired into the universe, or if any such periodicity is instead the product of subjective human interpretation, contingent upon the circumstances, beliefs and predilections of human observers. An objective basis for chemical periodicity would settle the questions about the location of hydrogen and helium, and the composition of group 3. Such an underlying truth, if it exists, is thought to have not yet been discovered. In its absence, the many different forms of periodic table can be regarded as variations on the theme of chemical periodicity, each of which explores and emphasizes different aspects, properties, perspectives and relationships of and among the elements. The ubiquity of the standard or medium-long periodic table is thought to be a result of this layout having a good balance of features in terms of ease of construction and size, and its depiction of atomic order and periodic trends. [49][113] See also Abundance of the chemical elements Atomic electron configuration table Element collecting List of elements List of periodic table-related articles Table of nuclides Timeline of chemical elements discoveries Notes 1. ^ The elements discovered initially by synthesis and later in nature are technetium (Z=43), promethium (61), astatine (85), francium (87), neptunium (93), plutonium (94), americium (95), curium (96), berkelium (97) and californium (98).
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