金属

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金属(metal)

具有高电导率、高热导率以及可塑性、延展性和高反光性的物质，在溶解时可以形成正离子和氢氧化物，其氧化物在遇水时并不产生酸。地球上有四分之三的元素属於金属，通常质地很硬，呈结晶状（参阅crystal）固体，能产生多种化学反应，并能同别的金属一起被制成合金。在元素周期表中，每一个垂直以及从右至左的表格中的金属元素的价由低向高呈上升趋势。最常见的金属有铝、铁、钙、钠、钾和镁，绝大多数都存在於矿石中，而不是游离状态。结晶状的黏着金属归结於金属的黏着性。其原子紧密结合，其周边活动的电子遍布在结构中。金属常被分为如下几类（但没有严格的区别，有可能出现重复的情况，定义不十分明确）：硷金属、硷土金属、过渡元素、贵重金属（稀有金属）、铂金、稀土金属、锕系金属、轻金属和重金属。许多金属元素在营养或其他生物化学中扮演重要的作用，通常以微量元素形式存在，在作为元素和化合物时，多数有毒（参阅mercury poisoning和lead poisoning）。

English version：

metal

Any of a class of substances with, to some degree, the following properties: good heat and electricity conduction, malleability, ductility, high light reflectivity, and capacity to form positive ions in solution and hydroxides rather than acids when their oxides meet water. About three-quarters of the elements are metals; these are usually fairly hard and strong crystalline (see crystal) solids with high chemical reactivity that readily form alloys with each other. Metallic properties increase from lighter to heavier elements in each vertical group of the periodic table and from right to left in each row. The most abundant metals are aluminum, iron, calcium, sodium, potassium, and magnesium. The vast majority are found as ores rather than free. The cohesiveness of metals in a crystalline structure is attributed to metallic bonding: The atoms are packed close together, with their very mobile outermost electrons all shared throughout the structure. Metals fall into the following classifications (not mutually exclusive and most not rigidly defined): alkali metals, alkaline earth metals, transition elements, noble (precious) metals, platinum metals, lanthanide (rare earth) metals, actinide metals, light metals, and heavy metals. Many have essential roles in nutrition or other biochemical functions, often in trace amounts, and many are toxic as both elements and compounds (see mercury poisoning, lead poisoning).

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