 Alkaline earth metals refer to the six elements belonging to the group IIA of the long form of the Modern Periodic Table, viz., Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra).  The name alkaline earth metals arose from the fact that the oxides of three metals of the group, viz. Ca, Sr and Ba, are alkaline in character and are found in nature as earths [lime (CaO), strontia (SrO) and baryta (BaO)].  Radium (Ra) has similar properties as other alkaline earth metals, but it is radioactive.

 The electronic structure of alkaline earth metals are given below: ElementAt. No. Complete Electronic ConfigurationValence-shell Electronic Configuration (ns 2 ) Be42, 2 or 1s 2 2s 2 2s 2 Mg122, 8, 2 or 1s 2 2s 2 2p 6 3s 2 3s 2 Ca202, 8, 8, 2 or 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 4s 2 Sr382, 8, 18, 8, 2 or 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 5s 2 5s 2 Ba562,8, 18, 18, 8, 2 or 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 2 5p 6 6s 2 6s 2 Ra882, 8, 18, 32, 18, 8, 2 or 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 6s 2 6p 6 7s 2 7s 2  These configurations show that the ultimate shell of these elements has two s-electrons (s 2 electrons) and the penultimate shell contains eight electrons (s 2 p 6 electrons).  When the two s-electrons are lost, alkaline earth metals are converted into M 2+ ions which have inert gas configuration.

1.Physical State: Alkaline earth metals have a grayish white luster when freshly cut and are malleable and ductile. 2.Density: These elements have higher density than those of the the alkali metals in the same period. Density decreases slightly up to Ca after which it increases. 3.Hardness: These elements are harder than alkali metals. 4.Melting & Boiling Points: Melting & boiling points of these elements are higher than those of alkali metals. But they do not show any regular trend. 5.Atomic Volume and Atomic & Ionic Radii: The atomic volumes and atomic & ionic radii of these elements are smaller than those of alkali metals in the same period. The values progressively increase in the same group from Be to Ra. 6.Colour of Ions: The ions of these elements have no unpaired electrons and consequently are colourless. 7.Ionization Energies: The ionization energies of these elements are quite low, but they are higher than those of alkali metals. The values progressively decreases when one proceeds down the group from Be to Ba. However, the value is slightly higher for Ra than that of Ba.

8.Electropositive Character: These elements show strong electropositve character which increases from Be to Ba. But their electropositivity is lower than the alkali metals. 9.Oxidation State: Alkaline earth metals show +2 oxidation state. 10.Hydration of Alkaline Earth Metals: The alkaline earth metal ions (M 2+ ) are strongly hydrated to form hydrated ions [M(H 2 O) x ] 2+. The hydration energies are higher than those of alkali metals. They decrease from Be 2+ to Ba 2+ with increase in ionic radii of M 2+ ions. 11.Flame Colouration: Except for Be & Mg, alkaline earth metals give characteristic colours to flame. Ca  Brick red; Sr  Crimson; Ba  Apple green; Ra  Red 12.Conductivity: Alkaline earth metals are good conductors of heat and electricity. 13.Reducing Properties: Alkaline earth metals are strong reducing agents. The oxidation potentials are lower than those of alkali metals. They increase on moving downward from Be to Ba. 14.Solubility of Salts: The salts of alkaline earth metals are less soluble than those of alkali metals.

1.Reaction with air (O 2 and N 2 ):  The alkaline earth metals react readily on heating with the oxygen (O 2 ) and the nitrogen (N 2 ) of the air to form oxides, MO and nitrides, M 3 N 2. 2M + O 2  2MO 3M + N 2  M 3 N 2  Be reacts less rapidly and requires high temperatures for the formation of BeO.  Ba forms peroxides, BaO 2, because of its greater activity. 2.Reaction with hydrogen (H 2 ):  Mg, Ca, Sr and Ba form hydrides when heated with hydrogen (H 2 ) : M + H 2  MH 2  These hydrides readily react with H 2 O to liberate H 2 : MH 2 + H 2 O  M(OH) 2 + H 2

3.Reaction with H 2 O:  Alkaline earth metals react readily with H 2 O to give hydroxide: M + 2H 2 O  M(OH) 2 + H 2  Be does not react with H 2 O even at elevated temperature. Mg reacts only with steam. 4.Reaction with acids: Alkaline earth metals react vigorously with acids to corresponding salts: M + 2HCl  MCl 2 + H 2 5.Reaction with halogens: Alkaline earth metals react with halogens (X 2 ) to form corresponding halides: M + X 2  MX 2

Beryllium Beryllium has never been used in medicine. It is now regarded as one of the most toxic element for common use. Magnesium  Magnesium is essential for life.  It acts as activator of many enzymes.  It is also important for neuromuscular functions. Official Magnesium Compounds: Magnesium Hydroxide NF [Mg(OH) 2 ]: Antacid, Laxative Magnesium Oxide USP (MgO) : Antacid, Laxative. A mixture of magnesium oxide, tannic acid and charcoal is well known as ‘universal antidote’. Magnesium Trisilicate USP [2MgO.3SiO 2.xH 2 O or (MgSiO 3 ) 2.SiO 2.xH 2 O): Antacid Talc USP (3MgO.4SiO 2.H 2 O): Lubricant, Filtering medium, Dusting powder

Calcium  Important for the function of nervous system.  Necessary for proper cardiac function.  Important factor in blood clotting.  Forms the structural basis of skeleton. Official Compounds Calcium Carbonate(CaCO 3 ): Externally as dentifrice; Internally as antacid; Source of calcium for calcium replacement therapy. Calcium Chloride USP (CaCl 2.2H 2 O): Source of calcium for calcium replacement therapy. Calcium Gluconate USP: Treatment of choice for hypocalcaemia and also in eczema Calcium Lactate NF: Calcium replacement therapy. Dibasic Calcium Phosphate NF: Source of calcium and phosphorus in pregnancy and in lactation and calcium deficiency states.

Strontium  Strontium itself has no medicinal value.  Strontium has been used as an adjuvant with calcium, in the form of strontium lactate, to promote remineralization of depleted skeleton.  No official compound is available currently. Barium  Barium is very toxic.  Barium ion produces local irritation.  Barium sulfate USP is used in X-ray diagnosis as a radioopaque medium in the alimentary tract. Radium  Radium is highly radioactive.  The radiation from radium can destroy living cells.  Radium salts are used to arrest and cure malignant growths.

Similarities: 1.Both the groups are s-block elements. 2.Both are electropositive. 3.Both have great chemical reactivity. 4.Both do not occur in the free state in nature. 5.Both are extracted by electrolytic method from their salts. 6.Both are silvery in untarnished conditions. 7.Both react with water to give metal hydroxides and H 2. 8.The hydroxides of both give strong bases with water.

Dissimilarities: 1.Alkaline earth metals are harder, heavier and have higher melting points than those of alkali metals. 2.Oxides and hydroxides of alkaline earth metals have more covalent character and are less basic compared to the alkali metals. 3.Ca, Sr and Ba react less vigorously with water than alkali metals. Be and Mg can survive in contact with water for a long time. 4.Carbonates and sulphates of alkaline earth metals are insoluble in water whereas those of alkali metals are soluble and undergo hydrolysis (except Li 2 CO 3 which is insoluble). 5.Phosphates of alkaline earth metals are insoluble in water whereas those of alkali metals are soluble (except Li 3 PO 4 which is insoluble).

 MADAN  HAIDER  ROGERS  BLOCK et. Al.