铈（Ce），化学元素，稀土金属中含量最高。
测验
元素周期表测验
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商业级铈的颜色是铁灰色，纯净时呈银色，并且和锡一样柔软和易延展。它在室温下在空气中氧化形成CeO 2。金属与水缓慢反应，迅速溶于稀酸中，但氢氟酸（HF）会导致形成保护性氟化物（CeF 3）层在金属表面上。铈车削（从锉削，磨削或加工金属时开始）在空气中容易自燃，炽热燃烧。它的自燃性是轻火石中重要的冶金应用之一。金属应在真空或惰性气氛中存储。该金属在室温下和室温以上均为中等强度的顺磁体，在13 K（-260°C或-436°F）以下变为反铁磁性。在超过20 kbar的压力下，它在Millikelvin范围内变得超导。
铈作为氧化物（氧化铈）由瑞典化学家JönsJacob Berzelius和Wilhelm Hisinger于1803年共同发现，并由德国化学家Martin Klaproth独立发现。它以小行星谷神星（Ceres）的名字命名，该谷神星于1801年发现。铈存在于菱镁石，独居石和许多其他矿物中。在铀，p和th的裂变产物中也发现了它。地壳火成岩中的铈含量约为铜的含量，约为铅的三倍。
Four isotopes occur in nature: stable cerium-140 (88.48 percent) and radioactive cerium-142 (11.08 percent), cerium-138 (0.25 percent), and cerium-136 (0.19 percent). Excluding nuclear isomers, a total of 38 radioactive isotopes of cerium have been characterized. They range in mass from 119 to 157 with half-lives as short as 1.02 seconds for cerium-151 and as long as 5 × 1016 years for cerium-142.
The metal is prepared by electrolysis of the anhydrous fused halides or by metallothermic reduction of the halides with alkali or alkaline-earth metals. It exists in four allotropic (structural) forms. The α-phase is face-centred cubic with a = 4.85 Å at 77 K (−196 °C, or −321 °F). The β-phase forms just below room-temperature and is double close-packed hexagonal with a = 3.6810 Å and c = 11.857 Å. The γ-phase is the room temperature form and is face-centred cubic with a = 5.1610 Å at 24 °C (75 °F). The δ-phase is body-centred cubic with a = 4.12 Å at 757 °C (1,395 °F).
Cerium compounds have a number of practical applications. The dioxide is employed in the optics industry for fine polishing of glass, as a decolourizer in glass manufacturing, in petroleum cracking catalysts, and as a three-way automotive emission catalyst that makes use of its dual valence (3+/4+) characteristics. Together with the other rare-earth metals, cerium is a constituent of numerous ferrous alloys to scavenge sulfur and oxygen and to nodulize cast iron. It is also used in nonferrous alloys, most commonly to improve high-temperature oxidation resistance of superalloys. Misch metal (typically 50 percent cerium, 25 percent lanthanum, 18 percent neodymium, 5 percent praseodymium, and 2 percent other rare earths) is primarily used for lighter flints and alloying additions.
铈与和ter不同，它与其他稀土元素的不同之处在于它会形成氧化态为+4的化合物。它是唯一在溶液中表现出+4氧化态的稀土。Ce 4+离子的盐（铈盐）是有力但稳定的氧化剂，用于分析化学中以确定可氧化的物质，例如亚铁（铁处于+2氧化态）。处于+3氧化态的铈表现为典型的稀土元素。
元素属性
| 原子数 | 58 |
|---|---|
| 原子重量 | 140.115 |
| 熔点 | 798°C（1,468°F） |
| 沸点 | 3,443°C（6,229°F） |
| 比重 | 6.7704（24°C或75°F） |
| 氧化态 | + 3，+ 4 |
| 电子配置 | [Xe] 4f 2 6s 2 |
