Salts of Main Group Metals

Group IA Group IIA
Group IIIA Group IVA

With the exception of aluminum, tin, and lead, the average citizen never comes in contact with the main group metals. The salts of these elements, however, have seemingly endless uses in our daily lives.


The "lithium" used to treat manic-depressive patients is not lithium metal but a lithium salt, such as lithium carbonate (Li2CO3). Sodium bicarbonate (NaHCO3) is sold as baking soda for use in cooking and as bicarbonate of soda for use as an antacid. It is even mixed with kitty litter, in which it serves as a deodorizer. Ordinary table salt (NaCl) is so important that it has entered our language in the form of cliches such as "salt of the earth," and "not worth his salt," and it is the source of the word "salary," which comes from the Latin salarium --money given to Roman soldiers to buy salt. The only potassium salt commonly used in cooking is cream of tartar, or potassium hydrogen tartrate (KHC4H4O6), which is used to transform baking soda into baking powder. Potassium salts are essential to plant nutrition, however, and potassium chloride (KCl), potassium nitrate (KNO3), and potassium sulfate (K2SO4) are used extensively in agriculture.

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Beryllium was once known as glucinium because so many of its compounds taste sweet.

Exposure to even small quantities of beryllium salts can be fatal, however, so beryllium plays no significant role in our daily lives. The best known magnesium salts are magnesium hydroxide, Mg(OH)2, and magnesium sulfate, MgSO4· 7 H2O. Mg(OH)2 is used in "milk of magnesia" to treat acid indigestion, and MgSO4 · 7 H2O can be found in "Epsom salts."

There are a number of important calcium salts. Calcium carbonate (CaCO3) is found in chalk, coral, egg shells, limestone, marble, pearl, and clam shells. CaCO3 decomposes on heating to form calcium oxide, or lime (CaO).

CaCO3(s) ----> CaO(s) + CO2(g)

Lime is used to neutralize soil that is too acidic, and it is the principal ingredient of cement.

Calcium sulfate occurs naturally as gypsum, CaSO4· 2 H2O. When heated, gypsum loses water to form plaster of Paris.

2 [CaSO4· 2 H2O(s)] ----> [(CaSO4)2 · H2O(s)] + 3 H2O(l)
gypsum plaster of Paris

When plaster of Paris is mixed with water, the reaction is reversed. This makes plaster of Paris useful for everything from plastering the interior of buildings to making casts to support broken bones.

The principal component of both bone and tooth enamel is a mineral known as hydroxyapatite, Ca5(PO4)3OH. The idea behind fluoridating water or adding fluorides to toothpaste is to convert a portion of the hydroxyapatite in tooth enamel into fluoro-apatite, Ca5(PO4)3F, which is a harder mineral and therefore more resistant to decay.

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Aluminum oxide (Al2O3) is found in nature as corundum, one of the hardest known minerals. Rubies are crystals of corundum that contain small quantities of chromium impurities and sapphires are crystals of corundum with trace quantities of iron or titanium. An aluminum salt with which many people have daily contact is "aluminum chlorhydrate," or more accurately, aluminum hydroxychloride, Al2(OH)5Cl · 2 H2O. This compound is an astringent, which contracts body tissues. When applied to underarms, its tendency to contract the pores of the skin makes it an antiperspirant.

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Tin(II) fluoride (SnF2), or stannous fluoride, was the first source of the fluoride ion used in toothpastes. Tin(IV) oxide, SnO2, is mixed with a variety of transition-metal oxides, such as V2O5 and Cr2O3, to form glazes of different colors for use with ceramics. Trialkyltin compounds such as (C4H9)3SnOH are important biocides used to control fungi, bacteria, insects, and weeds. These compounds have also been used to inhibit the formation of barnacles on ships' hulls.

Lead(II) oxide (PbO), or litharge, is often added to glass to increase its density, brilliance, and strength. PbO is also an important component of the lead storage batteries used in cars and trucks. At one time, lead chromate (PbCrO4) and lead dichromate (PbCr2O7) were important yellow and orange pigments for use in paint. As our awareness of the toxicity of lead compounds has increased, these pigments have gradually been replaced by others. Until recently, tetraethyl lead, Pb(C2H5)4, was routinely added to gasoline to increase its octane number. Concern over high levels of lead emissions from automobile exhaust has resulted in a switch to "unleaded" gasolines.

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