The S-Block elements

THE S-BLOCK ELEMENTSIntroductionModern chemical knowledge is based largely on principles that answer the “why” as well as the “how-to.”In the remaining chapters, we will emphasize facts and applications, but we will refer to underlying principles repeatedly.Four of the 14 elements that comprise the s-block elements are somewhat unusual cases, although not all for the same reason.Hydrogen is the simplest element, with one proton and one electron, and its behavior is rather special.Helium lies in the s-block but its electron configuration fits with the noble gases, and it will be considered in the next chapter.Francium and radium are highly radioactive and we will not consider them further.GROUP IA: THE ALKALI METALSSpodumene LiAl(SiO3)2The Alkali MetalsDiscoveries are recent. Sodium and potassium (1807) by electrolysis.Cesium (1860) and rubidium (1861) from emission spectra.Francium (1939) from actinium radioactive decay.Most salts are water soluble.Natural brines are good sources.Natural deposits allow mining of solids.Flame ColorsProperties and Trends in Group 1AThe Group 1A metals exhibit regular trends for a number of properties.Irregular trends suggest that factors are working against each other in determining a property (such as the density “discrepancy” between sodium and potassium).The alkali metals have two notable physical properties: they are all soft and have low melting points.When freshly cut, the alkali metals are bright and shiny—typical metallic properties. The metals quickly tarnish, however, as they react with oxygen in the air.Diagonal Relationships:The Special Case of LithiumIn some of its properties, lithium and its compounds resemble magnesium and its compounds.Lithium carbonate, fluoride, hydroxide, and phosphate are much less water soluble than those of other alkali metals.Lithium is the only alkali metal that forms a nitride (Li3N).When it burns in air, lithium forms a normal oxide (Li2O) rather than a peroxide or a superoxide.Lithium carbonate and lithium hydroxide decompose to form the oxide on heating, while the carbonates and hydroxides of other Group 1A metals are thermally stable.Diagonal RelationshipsThe elements in each encircled pair haveseveral similar properties.Occurrence, Preparation, Use, & Reactions of the Alkali MetalsSodium and potassium are isolated primarily from brines (solutions of NaCl and KCl).Lithium is obtained mostly from the mineral spodumene, LiAl(SiO3)2.To convert an alkali metal ion into an alkali metal atom, the ion must take on an electron—a process of reduction.This is not easy with the alkali metals; they are excellent reducing agents.Potassium was the first alkali metal to be prepared by electrolysis.Liquid sodium is used as a heat transfer medium in some types of nuclear reactors and in automobile engine valves, and its vapor is used in lamps for outdoor lighting.Potassium is used in making KO2, used as an oxygen source for miner’s “self-rescuers” and similar devices:Lithium is used in lightweight batteries of the type found in heart pacemakers, cellular telephones, digital cameras, and portable computers.Occurrence, Preparation, Use, & Reactions of the Alkali MetalsGroup I CompoundsHalidesNaCl 50 milliontons/year in U.S.Preservative, usedon roads, water softener regeneration,feedstock for other chemicalsKCl from natural brines. Plant fertilizers, feedstock.Important Compounds of Lithium, Sodium, and PotassiumLithium carbonate is the usual starting material for making other lithium compounds:Li2CO3(aq) + Ca(OH)2(aq)  CaCO3(s) + 2 LiOH(aq)One use of LiOH is to remove CO2 from expired air in submarines and space vehicles:2 LiOH(s) + CO2(g)  Li2CO3(aq) + H2ONaCl is the most important industrial sodium compound (50 million tons/yr).It is used to prepare a number of other chemicals and consumer products, including plastics, paper, bleach, soap, and laundry detergent.CarbonatesLi2CO3 is unstable relative to the oxide.Used to treat manic depression (1-2 g/day). Na2CO3 primarily used to manufacture glass.Currently mined from rich U.S. resources but can be manufactured by the Solvay process (E. Solvay, Belgium, 1838-1922).Production and Use2 NaCl(l) → 2 Na(l) + Cl2(g)Electrolysis:KCl(l) + Na(l) → 2 NaCl(l) + K(g)Sodium as a reducing agent: TiCl4 + 4 Na → Ti + 4 NaClPreparation of Sodium Compounds from NaClThe methods of preparation suggested by this diagram are not necessarily the preferred industrial methods.The Solvay Process—One Way to Diagram an Industrial ProcessThe Alkali Metals and Living MatterHydrogen, oxygen, carbon, and nitrogen are the most abundant elements in the human body, in the order listed.Sodium and potassium ions are in a second tier of seven elements that account for about 0.9% of the atoms. Sodium ions are found primarily in fluids outside cells and potassium ions are abundant in fluids within cells.Because most alkali metal compounds are water soluble, many drugs that are weak acids are administered in the form of their sodium or potassium salts.Lithium carbonate is used in medicine to level out the dangerous manic “highs” that occur in manic-depressive psychoses.Sodium SulfateH2SO4(conc. aq) + NaCl(s) → NaHSO4(s) + HCl(g)NaHSO4(s) + NaCl(s) → Na2SO4(s) + HCl(g)In the Kraft Process for making paper:Na2SO4(s) + 4 C(s) → Na2S(s) + 4 CO(g)45 kg/ton paperOxides and HydroxidesReaction with oxygen produces several ionic oxides. In limited oxygen supplies:M2O (small amounts of Li2O2 from Li).In excess oxygen:Li and Na form the peroxide, M2O2.K, Rb and Cs form the superoxide MO2.Soaps and DetergentsA soap acts by dispersing grease and oil films into microscopic droplets.The droplets detach themselves from the surfaces being cleaned, become suspended in water, and are removed by rinsing.The alkali metal soaps are water soluble; the alkaline earth metal soaps are not.A soap can function well in hard water only after a part of it is used up to precipitate all the alkaline earth metal ions present; in other words, the soap softens the water first.Detergents and SoapsCleaning Action of a SoapA soap has a hydrocarbon “tail” and an ionic “head”An oil droplet is attracted to the hydrocarbon tails, and the ionic ends permit the droplet to be solubilized in water.