Alkali Earth Metal

The alkaline earth metals are the following chemical elements beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). All of these elements have very similar properties: they are shiny, silvery-white and reactive metals. They are highly metallic and good conductors of heat and electricity, having a grey-white luster when freshly cut but tarnish readily in air because of oxidation.  

Because of their reactivity none of the alkaline earth metals are found in their elemental states. Beryllium occurs in the Earth's crust in law concentration of 2.8mg/kg. The number of stable isotope is 1.  The most common magnesium minerals found in the nature are carnallite (KCl x MgCl2 x 6H2O), magnesite (MgCO3) and dolomite (CaCO3 x MgCO3). Common calcium containing minerals are limestone (CaCO3) and gypsum (CaSO4x2H2O). Magnesium is the seventh most abundant element in the Earth's crust and the estimated abundance is 2.33x104mg/kg. Magnesium estimated abundance in the ocean is 1.29x103mg/lit. Calcium is the fifth most abundant element in the Earth's crust and the estimated abundance is 4.15x104mg/kg. Calcium estimated abundance in the ocean is 4.12x102mg/lit. Both magnesium and calcium have 3 stable isotopes each. Strontium is the fifteenth most abundant element in the Earth's crust and the estimated abundance is 3.7x102mg/kg. Strontium estimated abundance in the ocean is very low 7.9 mg/lit. The principal strontium containing minerals are celectite (SrSO4) and strontianite (SrCO3). The number of stable isotopes is 4. Barium is slightly less common in nature than strontium, mostly in the mineral barite (BaSO4) and witherite Ba(CO3). Barium has 6 stable isotopes. Radium is very unstable and radioactive substance with no stable isotopes. The estimated abundance in the Earth's crust is just 9x10-7mg/kg. Due to its relatively short half-life, radium from the Earth's early history has decayed and present day samples have all come from the much slower decay of uranium.

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Chemical properties of alkaline earth metals are defined by their electronic configuration. Each of these metal atoms has two electrons in its outermost shell and these valence electrons are much more weakly bound than the electrons in inner shells. That is why they readily lose their outermost electrons (ns2) to form cation with +2 charge. This way, they get the electronic configuration of a noble gas which is a preceding element in the periodic table. The oxidation number of each alkali metal is always +2. Chemically, the alkaline-earth metals are all strong reducing agents. The s electrons are relatively easily ionized (removed from the atom) and this ionization is characteristic feature of alkaline-earth chemistry. The ionization energy (the energy required to strip an electron from the atom) falls continuously in series from beryllium to radium. But the value of the ionization energy of alkaline-earth metals is higher than the ionization energy of alkali metals. Generally, the ionization energy increases in periodic table toward the right and decreases downward.

The alkaline-earth metals easily form ionic bond with non-metal elements from group 16 and 17 very easily. They have very similar chemical properties due to the fact that their electron configuration is ns2 in their outermost energetic shell. All of the alkaline-earth metals react with halogens and form halides, the ionic compounds, such as calcium chloride (CaCl2) or   magnesium bromide (MgBr2). When react with oxygen they form oxides such as magnesium oxide (MgO), calcium oxide (CaO) or strontium oxide (SrO). Magnesium, calcium, strontium and barium react with water and release hydrogen gas and thereby form strong caustic solution. Magnesium hydroxide and calcium hydroxide are known as very strong bases. The oxides of alkaline-earth metals are basic which means that react with water and form hydroxides. With carbon, the alkaline-earth metals form carbides, with sulfur form sulfides, with hydrogen form hydrides and with nitrogen form nitrides. In reaction with acids they release hydrogen gas and form salts. The most important alkaline-earth metals salts are: halides, sulfates, nitrates, nitrites and carbonates.    

With the exception of radium, all the metals and their compounds find commercial application to some degree. Magnesium is used for production of alloys with aluminium and zinc. It has important role in iron, steel and titanium production, as well. Calcium, as a reducing agent, is used in the separation of other metals from ore. It is also used in the production of aluminium and copper alloys. Calcium (as calcium carbonate) also has a role in production of mortars and cement. Strontium (as strontium carbonate) is used in the manufacturing of fireworks and pure strontium is used in the medical studies. Barium sulfate has many uses in petroleum industry.

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