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 their oxides, the alkaline earths. Early scientists called these compounds “earths” because they remain solid in a fire and are insoluble in water.
Natural Occurrence and Uses of Alkaline Earth Metals
Beryllium is a very light metal found in the minerals beryl and emerald. Fighter jet planes, internal guidance systems, and some race cars use beryllium or its alloys for their low density.
Magnesium metal is in sparklers, and is marketed in different forms as Epsom salt (magnesium sulfate) and milk of magnesia (magnesium hydroxide). It also plays an essential role in many biological processes including photosynthesis (as a component of chlorophyll) and enzymatic reactions in the human body (as a cofactor).
Calcium is essential for strong bones in the body and is found in calcite and aragonite, important minerals involved in earth’s carbon cycle.
Strontium gives fireworks their red color. The ratio of its different isotopes in teeth can tell archeologists about the diet of ancient humans.
Oil well drilling fluid includes barium sulfate, and geochemists can use barium chloride to determine the concentration of sulfate ions in water samples.
Discovery of Alkaline Earth Metals
An English chemist named Sir Humphry Davy isolated magnesium, calcium, barium, and strontium in 1808. He formed amalgams of the metals with mercury using electrolysis, then distilled off most of the mercury.
French scientist Nicolas-Louis Vauquelin discovered Beryllium in its oxide form in 1798. His fellow Frenchman Antoine Bussy and German chemist Friedrich Wöhler isolated the metallic form independently of one another in 1828.
Marie Curie and her husband Pierre made the discovery of radium much later in 1898. Their investigation of the radioactivity of radium as well as the post-transition metal polonium, earned the Curies a share in the 1903 Nobel Prize in Physics.
Properties of 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 2s orbital electrons that it loses are further away from the nucleus, and therefore more easily removed.
List of all Alkaline Earth Metals
Beryllium, magnesium, calcium, strontium, barium and radium.
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, meaning that it can act as either an acid or a base. 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 with addition of excess sodium sulfate, whereas magnesium sulfate is highly water-soluble.
Alkaline earth metal salts are generally colorless or white, but barium manganate, barium permanganate, barium dichromate, and barium chromate are strongly colored.
Fun facts about the Alkaline Earth Elements
- Beryllium is highly toxic, both in elemental form as dust and also in its compounds. It is 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 looking directly at it can be harmful.
- Magnesium plays a role in over 300 different enzyme reactions in the human body.
- Toothpastes designed for people with sensitive teeth often contain strontium chloride.
- 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 will be part of this group if scientists succeed in synthesizing it.
- 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.
Further Reading
The Halogen Elements
Learning Periodic Trends
The Periodic Table – how to read it
Periodic Table with Names