What are the Alkaline Earth Metals
The alkaline earth metals are the elements in the second group of the periodic table, starting with beryllium and ending with radium. They are all silvery-white, shiny metals that are fairly reactive, although not as reactive as the alkali metals. Most are commonly found in nature, but not in their elemental form. The name “alkaline earth” comes from the fact that they remain solid in a fire.
Beryllium is a very light metal, used in fighter jet planes and internal guidance systems. Magnesium metal is in sparklers, and magnesium sulfate is Epsom salts. It plays an essential biological role in our body. Calcium is essential for strong bones in the body, strontium gives fireworks their red color, and barium sulfate is used in oil well drilling fluid.
Sir Humphry Davy was an English chemist who isolated magnesium, calcium, barium, and strontium in 1808. He formed amalgams of the metals with mercury, and then distilled off most of the mercury. His method, was the electrolysis of a combination of the alkaline earth oxide with mercuric oxide, covered in a thin later of naphtha.
Properties of the Alkaline Earth Metals
Being in the second group, all of the alkaline earth elements have 2 electrons in their outer electron shell, in the s orbital. They all have significantly higher melting points than the alkali metals. They are generally softer and less dense than transition metals. Calcium is the lightest, and radium is the densest.
Magnesium and calcium are quite abundant in both the earth’s crust and in sea water. Beryllium is significantly rarer in the crust than the other 4 non-radioactive metals.
The reactivity of the alkaline earth metal increases as you move down the column. Beryllium does not react with water, magnesium reacts with steam, calcium reacts slowly with cold water, and strontium and barium more quickly. Barium is more reactive than the other metals, because the 2 s orbital electrons that it loses are further away from the nucleus, and therefore more easily removed.
List of all Alkaline Earth Metals
Alkaline Earth Chemistry
These elements have fairly similar chemistries. They exist almost exclusively in the +2 oxidation state. When they react with water, they form the hydroxide and hydrogen gas. Reaction with nitric acid or hydrochloric acid is quite vigorous, and concentrated nitric acid can release toxic nitrogen dioxide. However, these metals often do not react with sulfuric acid to a significant degree.
Beryllium chemistry is different than the other alkaline earth metals. Beryllium chloride, BeCl2 has covalent properties, and beryllium hydroxide, Be(OH)2 is amphoteric. It forms complexes more easily than the other metals. You can read more about the interesting chemistry of beryllium here.
It can be very difficult to separate magnesium from calcium in solution. However, calcium sulfate has very low solubility in water, especially when excess sodium sulfate is added, whereas magnesium sulfate is highly soluble.
Alkaline earth metal salts generally are colorless or white, although barium manganate, barium permanganate, barium dichromate, and barium chromate are examples of strongly colored salts.
Fun facts about the Alkaline Earth Elements
- Beryllium is highly toxic, both in elemental form as dust and also in its compounds. It is labeled a class 1 carcinogen.
- Soluble barium compounds are also quite toxic, although not as much as beryllium compounds.
- Magnesium metal is often sold as ribbon. This ribbon burns so brightly when ignited, that it should not be looked at directly.
- Magnesium plays a role in over 300 different enzyme reactions in the human body.
- Strontium chloride is added to toothpastes that are designed for people with sensitive teeth.
- Barium salts are often used to make pure acids by fixing them with sulfuric acid. The barium sulfate precipitates out, leaving only the conjugate acid of the barium salt.
- All isotopes of radium are radioactive, and many are luminescent.
- Element 120 is theoretically part of this group, but it has not been synthesized yet.
- The melting points and densities of the alkaline earth elements are difficult to predict based on their position.
- Marie Curie and her husband spent hundreds of hours refining tons of pitchblende in order to isolate 0.1 grams of radium chloride in 1902. Eight years later, she isolated elemental radium.