Section outline

  • Girl in a fur-lined coat holding a sparkler, surrounded by festive lights.

    Sparklers like the one this girl is holding make festive additions to many celebrations. You may use them yourself. But watch out if you do because their flames are really hot! The bright white flames are produced when magnesium burns. Magnesium is a light- metal that burns at a very high . Other uses of magnesium include flash photography, flares, and fireworks. Magnesium is a metal in group 2 of the periodic table , which you will read about in this concept.
    ::像这个女孩拿着的闪光灯一样的闪光灯, 给许多庆祝活动增添了节日活动, 你可以自己使用。 但请注意, 如果你这样做, 因为他们的火焰非常热! 镁燃烧时会产生明亮的白色火焰。 镁是一种光金属, 在非常高的温度下燃烧。 镁的其他用途包括闪光摄影、 照明弹和烟火。 镁是周期表第2组的金属, 你会从这个概念中读到。

    The Second Group
    ::第二集团

    Barium (Ba) is one of six in group 2 of the periodic table, which is shown in Figure . Elements in this group are called alkaline Earth metals . These are silver or gray in color. They are relatively soft and low in density, although not as soft and lightweight as alkali metals . 
    ::Bior(Ba)是周期表第2组中的6个之一,如图所示。这一组中的元素称为碱性地球金属,其颜色为银色或灰色,密度相对软,低,尽管不象碱性金属那么软和轻。

    Periodic table highlighting alkaline Earth metals, including Barium (Ba) and its group members.

    Reactivity of Alkaline Earth Metals
    ::Alkaline地球金属的反作用

    All alkaline Earth metals have similar properties because they all have two . They readily give up their two valence electrons to achieve a full outer , which is the most stable arrangement of electrons. As a result, they are very reactive, although not quite as reactive as the alkali metals in group 1. For example, alkaline Earth metals will react with cold water, but not explosively as alkali metals do. Because of their reactivity , alkaline Earth metals never exist as pure substances in nature. Instead, they are always found combined with other elements.
    ::所有碱性地球金属都具有相似的特性,因为它们都有两个。它们很容易放弃其两个价值电子,以达到一个完整的外部,这是最稳定的电子组合。因此,它们非常反应性,虽然没有第1组碱性金属那么被动,但与第1组碱性金属相比,碱性地球金属会与冷水发生反应,而不是与碱性金属发生爆炸性反应。由于其反应性作用,碱性地球金属在自然界中从未像纯物质那样存在,相反,它们总是与其他元素一起被发现。

    The reactivity of alkaline Earth metals increases from the top to the bottom of the group. That’s because the atoms get bigger from the top to the bottom, so the valence electrons are farther from the nucleus . When valence electrons are farther from the nucleus, they are attracted less strongly by the nucleus and more easily removed from the . This makes the atom more reactive.
    ::碱性地球金属的反作用从组的上到下增加。 这是因为原子从上到下变大,因此价值电子离核更远。 当值电子离核更远时,它们被核心吸引的力度较小,更容易从中移除。这使得原子更具反应性。

    Q: Alkali metals have just one valence . Why are alkaline Earth metals less reactive than alkali metals?
    ::问题:碱性金属只有一个价值。为什么碱性地球金属的活性比碱性金属少?

    A: It takes more to remove two valence electrons from an atom than one valence electron. This makes alkaline Earth metals with their two valence electrons less reactive than alkali metals with their one valence electron.
    ::A:从原子上除去两个值电子比一个值电子要花更多时间。这使得碱性地球金属用其两个值电子比碱性金属用其一个值电子少活性。

    Examples of Alkaline Earth Metals
    ::Alkaline地球金属实例

    For a better understanding of alkaline Earth metals, let’s take a closer look at two of them: calcium (Ca) and strontium (Sr). Calcium is a soft, gray, nontoxic alkaline Earth metal. Although pure calcium doesn’t exist in nature, calcium compounds are very common in Earth’s crust and in sea water. Calcium is also the most abundant metal in the human body, occurring as calcium compounds such as calcium phosphate and calcium carbonate. These calcium compounds are found in bones and make them hard and strong. The skeleton of the average adult contains about a kilogram of calcium. Because calcium—like barium—absorbs , bones show up white in images. Calcium is an important component of a healthy human diet. Good food sources of calcium are pictured in Figure .
    ::为了更好地了解碱性地球金属,让我们仔细看看其中两种金属:钙(Ca)和(Sr)。钙是一种软的、灰的、无毒性的碱性地球金属。虽然纯钙在自然中并不存在,但钙化合物在地球的地壳和海水中非常常见。钙也是人体中最丰富的金属,如磷酸钙和碳酸钙等钙化合物。这些钙化合物在骨头中找到,并且硬的和坚固的。普通成年人的骨骼中含有大约一公斤钙。因为钙(类似--)的骨骼在图像中显示出白色。钙是人体健康饮食的重要组成部分。在图中描绘出良好的钙食物来源。

    Various food sources rich in calcium, including milk, cheese, yogurt, and fruits.

    Q: What health problems might result from a diet low in calcium?
    ::问题:低钙饮食可能导致哪些健康问题?

    A: Children who don’t get enough calcium while their bones are forming may develop a deficiency disease called rickets, in which their bones are softer than normal and become bent and stunted. Adults who don’t get enough calcium may develop a condition called osteoporosis, in which the bones lose calcium and become weak and brittle. People with osteoporosis are at high risk of bone fractures.
    ::甲:在骨骼形成时得不到足够的钙的儿童可能会发展出一种叫做的缺血性疾病,在这种疾病中,他们的骨头比正常人柔软,弯曲和发育迟缓。 得不到足够的钙的成年人可能会发展出一种叫做骨质疏松症的症状,在这种疾病中,骨头会失去钙,变得虚弱和易碎。 骨质疏松症患者的骨折风险很大。

    Strontium is a silver-colored alkaline Earth metal that is even softer than calcium. Strontium compounds are quite common and have a variety of uses—from fireworks to cement to toothpaste. In fireworks, strontium compounds produce deep red explosions. In toothpaste, the strontium chloride reduces tooth sensitivity.
    ::是一种银色的碱性地球金属,甚至比钙软。 化合物非常常见,有多种用途——从烟花到水泥到牙膏,在烟花中,化合物产生深红色爆炸,在牙膏中,氯化物降低牙敏度。

    Summary
    ::摘要

    • Elements in group 2 of the periodic table are called alkaline Earth metals. They are silvery or gray in color. They are also relatively soft and low in density.
      ::周期表中第2组元素称为碱性地球金属,彩色为银色或灰色,密度也相对软和低。
    • Alkaline Earth metals are very reactive because they readily give up their two valence electrons to achieve a full outer energy level, which is the most stable arrangement of electrons. Reactivity increases from the top to the bottom of the group.
      ::碱性地球金属非常具有反应性,因为它们很容易放弃两种价值电子,以达到完全的外能水平,这是最稳定的电子组合。反应从组的上到下增加。
    • Examples of alkaline Earth metals include calcium, which is needed for strong bones, and strontium, which is used for making cement and other products.
      ::碱性地球金属的例子包括坚固骨头需要的钙和用于制造水泥和其他产品的。

    Review
    ::回顾

    1. What are alkaline Earth metals? What are their physical properties?
      ::什么是碱性地球金属?它们的物理特性是什么?
    2. Why are alkaline Earth metals very reactive?
      ::为什么碱性地球金属反应性很强?
    3. Compare and contrast the reactivity of beryllium (Be) and barium (Ba).
      ::比较和对比(Be)和(Ba)的回活动。

    Explore More
    ::探索更多

    O bserve how four different alkaline Earth metals react with water in the video below. Then, answer the questions that follow.
    ::观察以下视频中四种不同的碱性地球金属如何与水发生反应。 然后回答下面的问题。

     

     

     

    1. Observe the reactions in the video, and then rank the alkaline Earth metals from most to least reactive with water.
      ::观察视频中的反应,然后将碱性地球金属从大部分与水的反应从最低排到最低。
    2. What explains the differences in reactivity?
      ::反应的差别是什么?
    3. Predict the reactivity of beryllium with water. Where would it fit in your ranking?
      ::预测与水的回弹性。 它适合你的排名吗 ?
    4. What substances are produced in each reaction that you observed in the video?
      ::在视频中你观察到的 每种反应中 都产生了哪些物质?