什麼是過渡元素及其化合物

價電子處在兩個殼層而不是一個殼層裡的任何化學元素。這種結構使它們具有與眾不同的能力，能夠組成包含多於一個原子的離子（複雜離子，或稱配位化合物），有一箇中心原子或離子（往往是過渡金屬離子），周圍是規則排列的配合基。這些離子的鍵合理論尚在完善中。週期表中從鈧到銅（原子序數21～29）、從釔到銀（39～47）以及從鑭到金（57～79，包括鑭系）是經常指的三組主要過渡系列。（錒系及以上原子序數89～111的元素也符合過渡元素的條件。）它們全都是金屬，許多具有重要的經濟或工業價值（例如鐵、金、鎳、鈦）。大部分密度較高、質地堅硬、脆性、導熱和導電性好、熔點高、彼此間以及與其他金屬能生成合金。它們的電子結構使它們在化合物中有多種價鍵。其中許多是有色金屬和順磁體（參閱paramagnetism），往往可用作催化劑。

transition element

Any chemical element with valence electrons in two shells instead of only one. This structure gives them their outstanding ability to form ions containing more than one atom (complex ions, or coordination compounds), with a central atom or ion (often a transition metal ion) surrounded by ligands in a regular arrangement. Theories on the bonding in these ions are still being refined. The elements in the periodic table from scandium to copper (atomic numbers 21-29), yttrium to silver (39-47), and lanthanum to gold (57-79, including the lanthanide series) are frequently designated the three main transition series. (Those in the actinide series and beyond, 89-111, also qualify.) All are metals, many of major economic or industrial importance (e.g., iron, gold, nickel, titanium). Most are dense, hard, and brittle, conduct heat and electricity well, have high melting points, and form alloys with each other and other metals. Their electronic structure lets them form compounds at various valences. Many of these are colored and paramagnetic (see paramagnetism) and often act as catalysts.