Transition elements - Sen'igenso

According to the IUPAC definition, an element with an incompletely filled d subshell, or an element that produces a cation with such a d subshell. Groups 3 to 11 of the long periodic table. Strictly speaking, it refers to elements 21 (Sc) to 29 (Cu) (first transition series), 39 (Y) to 47 (Ag) (second transition series), 57 (La) to 72 (Hf) to 79 (Au) (third transition series), 89 (Ac) and 103 (Lr) to 111 (Rg) (fourth transition series). Zinc, cadmium, mercury, and (112 (Copernicium)) from group 12 are sometimes added due to their similar properties. The elements with incomplete f-shells, from lanthanum (La) to lutetium (Lu) to actinium (Ac) to lawrencium (Lr) are called inner transition elements. The IUPAC Nomenclature of Inorganic Compounds (1990) states that lanthanides and actinides are also included in the transition elements. The name transition elements originated from the fact that when DI Mendeleev classified the elements in the periodic table, the iron and platinum group elements were transiently placed between the highly electronegative halogens (Group VII) and the highly electropositive alkali metals (Group I). All transition elements are heavy metals and are also called transition metals. The ionization energy, atomic radius, and other properties of elements belonging to the same series (same period) change more slowly than those of typical elements, and their properties are similar to each other. This tendency is particularly pronounced with the inner transition elements, which makes them difficult to separate from one another. Many of these elements are important metallic materials, including iron, copper, nickel, chromium, titanium, molybdenum, and tungsten, and they exhibit a wide variety of physical properties when alloyed with one another. Compounds of transition elements have incomplete electron shells, so many of them are paramagnetic. They also tend to form complexes, and many of them are colored. Since the same transition element can take on various oxidation states, many of them are important as oxidizing and reducing agents (KMnO ₄ , K ₂ Cr ₂ O ₇ , FeSO ₄ , TiCl ₃ , etc.). Elements with high oxidation numbers are acidic, those with low oxidation numbers are basic, and those in intermediate oxidation states tend to be amphoteric.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

IUPACの定義によれば，不完全に満たされたd亜殻をもつ元素，またはそのようなd亜殻をもつ陽イオンを生じる元素．長周期表の3族から11族元素．厳密には21番元素のスカンジウムScから29番の銅Cu(第一遷移系列)，39番のイットリウムYから47番の銀Ag(第二遷移系列)，57番のランタンLa，72番のハフニウムHfから79番の金Au(第三遷移系列)，89番アクチニウムAc，103番のローレンシウムLrから111番のレントゲニウムRg(第四遷移系列)をいう．性質の類似から12族の亜鉛，カドミウム，水銀，(112番コペルニシウム)を加えることもある．f亜殻が不完全な57番ランタンLaから71番ルテチウムLu(ランタノイド)，および89番のアクチニウムAcから103番のローレンシウムLr(アクチノイド)を内部遷移元素(inner transition elements)という．IUPACの無機化合物命名法(1990年)はランタノイド，アクチノイドも遷移元素に含まれるとしている．遷移元素という名称の起こりは，D.I. Mendeleev(メンデレーエフ)が周期表によって元素を分類したとき，陰性の強いハロゲン(Ⅶ族)と陽性の強いアルカリ金属(Ⅰ族)との間に，鉄族および白金族元素が第Ⅷ族元素として過渡的に介在していたことにちなんでいる．遷移元素の単体はいずれも重金属で，遷移金属ともよばれる．同一系列(同一周期)に属する元素のイオン化エネルギー，原子半径などの変化は，典型元素に比べて緩やかで，互いの性質が似通っている．この傾向は内部遷移元素でいちじるしく，したがって相互分離が困難であった．鉄，銅をはじめ，ニッケル，クロム，チタン，モリブデン，タングステンなど金属材料として重要なものが多く，相互に合金をつくることによって多様な物性を発揮する．遷移元素の化合物は不完全な電子殻をもっているため，常磁性を示すものが多い．また，錯体を形成しやすく，有色のものが多い．遷移元素は同一元素が種々の酸化状態をとるため，酸化剤，還元剤として重要なものも少なくない(KMnO₄，K₂Cr₂O₇，FeSO₄，TiCl₃など)．また，酸化数の高いものは酸性，低いものは塩基性を示し，中間の酸化状態のものは両性を示す傾向がみられる．

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