Group 2 Elements: The Alkaline Earth Metals | 第2族元素：碱土金属

📚 Group 2 Elements: The Alkaline Earth Metals | 第2族元素：碱土金属

The Group 2 elements are a family of metals found in the second column of the periodic table. They are called the alkaline earth metals because their oxides and hydroxides are alkaline and they are found in Earth’s crust. This article explains their structure, reactions, trends and important uses.

第2族元素是元素周期表第二列中的一族金属。它们被称为碱土金属，因为它们的氧化物和氢氧化物呈碱性，并且存在于地壳中。本文将解释它们的结构、反应、变化趋势和重要用途。

1. Meet the Group 2 Elements | 认识第2族元素

The Group 2 family includes beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). At KS3 level we usually focus on magnesium, calcium and sometimes barium, because beryllium is quite different and radium is radioactive.

第2族包括铍 (Be)、镁 (Mg)、钙 (Ca)、锶 (Sr)、钡 (Ba) 和镭 (Ra)。在 KS3 阶段，我们通常关注镁、钙，有时关注钡，因为铍的性质比较特殊，而镭具有放射性。

All Group 2 elements are shiny, silvery metals when freshly cut. They are harder than Group 1 metals and have higher melting points, but they are still less hard and lower melting than typical transition metals such as iron.

所有第2族元素在刚切开时都是有光泽的银白色金属。它们比第1族金属更硬、熔点更高，但仍不如铁等典型过渡金属坚硬，熔点也较低。

2. Where Are They in the Periodic Table? | 它们在周期表中的位置

Group 2 elements sit in the second column from the left, between Group 1 (the alkali metals) and the transition metals. They are in the s-block because their outer electrons occupy an s orbital.

第2族元素位于周期表左起第二列，介于第1族（碱金属）和过渡金属之间。它们属于 s 区，因为它们的最外层电子占据 s 轨道。

Moving down the group from beryllium to radium, the atoms gain extra electron shells. This makes the atoms larger and the outer electrons further from the nucleus.

从铍到镭，沿族向下，原子获得额外的电子层。这使得原子半径增大，最外层电子离原子核更远。

3. Physical Properties and Trends | 物理性质与变化趋势

The physical properties of Group 2 metals show some clear trends. Atomic radius and density increase down the group. Reactivity with water and acids also increases down the group because the outer electrons are easier to lose from larger atoms.

第2族金属的物理性质表现出一些明显的趋势。原子半径和密度沿族向下增大。与水和酸的反应活性也沿族向下增强，因为原子越大，越容易失去最外层电子。

The metals become softer as you go down the group, and they have higher melting points than Group 1 metals. However, melting points do not show a simple regular pattern because the packing of metal ions and the number of delocalised electrons both change.

沿族向下，金属变得更软，且熔点高于第1族金属。然而，熔点的变化没有简单的规律，因为金属离子的堆积方式和离域电子数都会发生变化。

Beryllium is an exception in several ways: it is very hard, has a high melting point, and its compounds often show covalent character rather than simple ionic behaviour.

铍在多个方面比较特殊：它非常坚硬，熔点很高，其化合物往往表现出共价性，而不是简单的离子行为。

4. Electronic Structure: Two Outer Electrons | 电子结构：两个最外层电子

Every Group 2 atom has two electrons in its outermost shell. For example, magnesium has the electronic structure 2,8,2. Calcium has the electronic structure 2,8,8,2. This gives them similar chemistry because they all lose the same number of outer electrons.

每个第2族原子的最外层都有两个电子。例如，镁的电子结构是 2,8,2；钙的电子结构是 2,8,8,2。这使得它们的化学性质相似，因为它们都会失去相同数目的最外层电子。

When a Group 2 metal reacts, each atom loses its two outer electrons to form a 2+ ion.

当第2族金属发生反应时，每个原子失去两个最外层电子，形成 2+ 离子。

Mg → Mg²⁺ + 2e⁻

Ca → Ca²⁺ + 2e⁻

This is different from Group 1 metals, which lose only one outer electron to form 1+ ions. The 2+ charge means Group 2 ions attract negative ions more strongly, which affects properties such as solubility and melting point.

这与第1族金属不同，第1族金属只失去一个最外层电子，形成 1+ 离子。2+ 电荷意味着第2族离子更强烈地吸引负离子，从而影响溶解度和熔点等性质。

5. Reaction with Water | 与水的反应

Group 2 metals react with water to form a metal hydroxide and hydrogen gas. The reaction becomes more vigorous as you go down the group: beryllium does not react with water, magnesium reacts very slowly with cold water but faster with steam, calcium reacts steadily, and barium reacts rapidly.

第2族金属与水反应生成金属氢氧化物和

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