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碱土金属 (n.)
碱土金属 (n.)
合金, 金, 金属, 金属元素, 金屬[Hyper.]
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Wikipedia
碱土金属指的是元素周期表上第 2 族(ⅡA族)的六个金属元素,包括鈹、鎂、鈣、鍶、鋇 和放射性元素鐳。
鹼土金屬都是銀白色的,比較軟的金屬,密度比較小。鹼土金屬在化合物中是以+2的氧化態存在。鹼土金屬原子失去電子變為陽離子時,最外層一般是8個電子,但铍離子最外層只有2個電子。
碱土金属都是活泼金属[1]。
目录 |
元素名称 |
主要化合价 |
硬度(金刚石=10) |
单质沸点(℃) |
焰色試驗結果 |
||||||
---|---|---|---|---|---|---|---|---|---|---|
铍 | Be | 0.105 | +2 | 固体 | 1.848 | 4 | 1278 | 2970 | 1.5 | 无焰色 |
镁 | Mg | 0.150 | +2 | 固体 | 1.738 | 2.0 | 650 | 1090 | 1.2 | 无焰色 |
鈣 | Ca | 0.180 | +2 | 固体 | 1.55 | 1.5 | 842 | 1484 | 1.0 | 磚紅色[1] |
鍶 | Sr | 0.200 | +2 | 固体 | 2.63 | 1.8 | 777 | 1382 | 1.0 | 紅色[1] |
鋇 | Ba | 0.215 | +2 | 固体 | 3.510 | 1.25 | 727 | 1870 | 0.9 | 蘋果綠[1] |
鐳 | Ra | 0.215 | +2 | 固体 | 5.000 | 1.03 | 700 | 1737 | 0.9 | 无资料 |
鹼土金屬和水的反應較碱金屬與水的反應要溫和,不像鹼金屬中的鈉和鉀在室溫中就會和水反應。而鎂和冷水反應缓慢,在热水或水蒸汽才较为剧烈,鈣常温下可以和冷水剧烈反应。
镁还能形成氮化物(氮化镁),钡和氧气加热下反应除了得到氧化钡,还能得到过氧化钡(过氧化钡可以吸氧、放氧,用来提取大气中的氧气[3])。
碱土金属的离子氢化物是强还原剂,其和水的反应方程式通式为:
除鎂和鍶外所有鹼土金屬都至少有一個放射性同位素,其中鈹-7、鈹-10和鈣-41是微量放射性同位素。鈣-48和鋇-130由於有很長的半衰期,因此它們都存在於大自然。
鈣和鎂都在地殼中常見,它們分別是現時地球蘊藏量第五多和第八多的元素。這兩個元素在地殼形成數種的礦物,如白雲石、石灰石和方解石等。其他非放射性元素在地球的蘊藏量較少,但也形成礦物,如綠柱石(鈹)、天青石(鍶)和重晶石(鋇)等。放射性元素鐳最長的半衰期只達1601年,因此它只是由其他較重的元素經放射性衰變所得,從而在大自然出現。
左方一族: | 碱土金属 第2族(ⅡA) |
右方一族: |
碱金属 | 3族元素 |
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