Alkaline earth metals, which are under Group 2 (the second column) of the periodic table, are highly reactive metals, though they’re not as reactive as the alkali metals. Their high reactivity is the main reason they aren’t found in a pure or elemental form in nature. Structurally speaking, these metals have two valence electrons in their outermost energy level.
Many of the compounds formed by the alkaline earth metals are essential to life, and have historically been used for diagnostic and therapeutic purposes. Others have industrial and commercial applications. This group even has a radioactive element made famous by the discovery and scientific investigations of Marie and Pierre Curie in the late 1800s.
What Are the Characteristics of Group 2?
Elements that belong to the same group have similar chemical and physical properties. Group 2 elements are all metals that are good conductors of heat and electricity in pure form. However, the descriptive name ‘alkaline earth’ has pre-periodic table origins.
Before the systematisation of the periodic table of elements by Dmitri Mendeleev in 1869, some compounds were mistaken as elements. For instance, non-metallic substances that cannot be dissolved in water or changed by fire were classified as earth elements. Oxides of Group 2 elements, such as calcium oxide, were thus classified as alkaline earths because they form caustic or corrosive products when they react with water. Calcium oxide, for example, doesn’t simply dissolve in water, but reacts with water to form calcium hydroxide.
Alkaline earth metals lose electrons easily, becoming positive ions or cations. Therefore, the compounds they form are ionic compounds, or salts. The metal ion is positively charged and represented by M2+, with the M standing for any metal element of Group 2.
Almost all the elements of Group 2 and their compounds have significant commercial applications, especially magnesium, which is used in combination with other metals to form useful alloys. A wide variety of calcium compounds, such as the oxides, also have commercial and industrial applications. In fact, magnesium and calcium are amongst the six most abundant elements on earth, and are intrinsic to many geological and biological processes.
Radium is the heaviest of all the alkaline earth metals. It’s the only element in the group whose isotopes, all 25 of them, are radioactive. Radium has no significant commercial use because of its rarity. Although once used for treating cancer, it has been replaced by less expensive radioactive elements.
What Are the Elements Included in Group 2?
Group 2 has six elements with similar chemical and physical properties. For instance, all the elements under this group are soft silver metals in pure form, and are all relatively less metallic compared to the elements of Group 1. They’re also highly reactive and unstable in that they don’t occur in element form in nature, but rather in combination with other elements, such as oxygen.
In terms of chemical reactions, the Group 2 metals also have similar reactions with other elements. The following are some of the main reactions:
- They all react with hydrogen to form hydrides
- They all react with oxygen to form oxides
- They can only react with nitrogen at extremely high temperatures
- They readily react with halogens (Group 17), forming metal halides
- Except for beryllium, all other alkaline earth metals react with water to form hydroxides and release hydrogen
Here are some of the chemical and physical properties of the individual elements of Group 2:
- Beryllium (Be): A very rare element not only on earth, but also in the entire known universe, beryllium was identified in 1798 by Louis-Nicolas Vauquelin. It naturally occurs in compounds as constituents of minerals. It can resist a wide range of temperatures and it’s a relatively light metal, making it suitable for many mechanical applications. For example, it’s used in the production of aircrafts in nozzles of liquid-fueled spacecrafts. It’s also used as mirrors in weather satellites. The optics of the Spitzer Space Telescope, for instance, are made from beryllium.
- Magnesium (Mg): Sir Humphry Davy discovered this element in 1808. It’s the eighth most common element in our planet’s crust. In pure form, it’s highly combustible, making it an ideal ingredient for fireworks. It’s used in car engines as part of alloys, and in many electronic devices. It also has a vital role in biological life as an ion and plays a part in the process of photosynthesis.
- Calcium (Ca): In the same year that Sir Humphry Davy discovered magnesium, he also isolated calcium through electrolysis of lime and mercuric acid. This element is essential in biological life as ions in electrolytes, carrying nerve signals. It’s also a very important component of bones, and is a mineral component of cement and mortar.
- Strontium (Sr): Adair Crawford discovered this element in 1790. It was named after Strontian, a village where it was discovered. In fireworks, it produces scarlet colours, and it’s also used in alloys.
- Barium (Ba): In the early 1600s, Vincenzo Casciarolo discovered some interesting pebbles that would shine at night when heated during day time. These pebbles were a mineral of barium known as barium sulphate, which has the chemical formula BaSO4. In 1808, Sir Humprey Davy extracted the metal through the electrolysis of barium hydroxide.
- Radium (Ra): As we mentioned earlier, this is the only element in Group 2 whose isotopes are all radioactive. It’s not considered a primordial element. It only occurs as a transition element derived from the radioactive decay chain of uranium and thorium. In the early 20th century, it was used in radiologic therapy for cancer, but was later replaced by more affordable alternatives.
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Original post: A Level Chemistry Revision: Inorganic Chemistry – Group 2, The Alkaline Earth Metals. No Republication or Redistribution allowed without written consent. Contact ReAgent Chemicals for more information.
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