# General Chemistry/Chemistries of Various Elements/Group 2

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## Alkaline Earth Metals

Pure magnesium crystals

The alkaline earth metals are the elements in Group 2 (2A). They are beryllium, magnesium, calcium, strontium, barium, and radium. They are less reactive than alkali metals, but they form (except for beryllium) alkaline oxides and hydroxides.

Alkaline earth metals all have two valence electrons, and they easily oxidize to the +2 state. With increasing mass, these elements become softer, have lower melting and boiling points, and become more reactive. None appear uncombined in nature, and all are separated from their compounds with difficulty. Alkaline earth metals react with halogens and (except for beryllium) with water and oxygen. Magnesium, being less reactive, reacts only at higher temperatures than the other alkaline earth metals. Radium is radioactive, so its chemical properties are difficult to study.

The alkaline earth metals are chemically and physically similar to the alkali metals, but they are less reactive.

## Reactions

The alkaline earth metals undergo reactions similar to the alkali metals, but their +2 oxidation state causes their compounds to be different. The following reactions use magnesium as an example, but the other alkaline earth metals undergo the same reactions as well.

 ${\displaystyle 2{\hbox{Mg}}_{(s)}+{\hbox{O}}_{2(g)}\to 2{\hbox{MgO}}_{(s)}}$ Magnesium oxide forms slowly unless ignited. Powders or thin slices of magnesium can be ignited with a match, so magnesium is used in fire-starting devices. ${\displaystyle 3{\hbox{Mg}}_{(s)}+{\hbox{N}}_{2(g)}\to {\hbox{Mg}}_{3}{\hbox{N}}_{2(s)}}$ Magnesium burns readily in oxygen, and surprisingly nitrogen as well. Air is composed mostly of nitrogen, but most elements will not react with nitrogen because nitrogen is so stable. ${\displaystyle {\hbox{MgO}}_{(s)}+{\hbox{H}}_{2}{\hbox{O}}_{(l)}\to {\hbox{Mg}}({\hbox{OH}})_{2(aq)}}$ Magnesium oxide is a basic anhydride. Magnesium hydroxide is a strong base, although its solubility is too low for this property to be significant. ${\displaystyle {\hbox{Mg}}_{3}{\hbox{N}}_{2(s)}+6{\hbox{H}}_{2}{\hbox{O}}\to 3{\hbox{Mg}}({\hbox{OH}})+2{\hbox{NH}}_{3(g)}}$ Magnesium nitride will react with water or the moisture in air. This reaction is detected by the pungent smell of ammonia. ${\displaystyle {\hbox{Mg}}_{(s)}+2{\hbox{H}}_{2}{\hbox{O}}\to {\hbox{Mg}}({\hbox{OH}})_{2(aq)}+{\hbox{H}}_{2(g)}}$ Magnesium metal reacts with water to form a hydroxide, but only at high temperatures or in the presence of acid. Calcium, being more reactive, will react with water as long as its hot. The other elements will react in warm water. Notice the flammable hydrogen gas that is released. ${\displaystyle {\hbox{Mg}}_{(s)}+2{\hbox{HCl}}_{(aq)}\to {\hbox{MgCl}}_{2(aq)}+{\hbox{H}}_{2(g)}}$ Magnesium will react exothermically with acids to form an ionic salt and hydrogen gas.

Remember that all of the alkaline earth metals can undergo these reactions; magnesium was just an example. Beryllium, however, is much less reactive than the other metals, so it might not react.

## Uses

Beryllium is rare and its compounds are very toxic, which makes processing it something limited to specialists trained in dealing with it safely. It is the lightest element that is sturdy enough to be used for construction and it is used for windows of X-ray tubes. Its absorption of X-rays is very small, because it only has 4 electrons per atom.

Magnesium metal has some use in applications needing a soft, light metal. Magnesium metal can be used an easily-burned substance with a bright light in photographic flash bulbs. Magnesium hydroxide is commonly used as a strong but generally safe antacid. Magnesium sulfate is commonly known as Epsom salts.

Even more significantly, magnesium appears in a compound known as chlorophyll, the greenish pigment in plants and algae that allows plants to perform photosynthesis. It is essential to animal life.

Calcium has no use as a structural metal, but its compound calcium carbonate is a major building material as limestone. Calcium carbonate is essential to bones and to plant life. Calcium and heavier elements in this group react with warm water to form highly-alkaline hydroxides.

Strontium, much rarer than calcium, has few uses. Barium, also rarer, has few uses other than its sulfate, a coating used for lining the digestive organs for X-rays. Compounds of barium soluble in either water or acids (but not the sulfate) are highly toxic.