Bài giảng Hóa học - Chương 8: Nhóm IA

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Nội dung Text: Bài giảng Hóa học - Chương 8: Nhóm IA

THE S-BLOCK ELEMENTS
Introduction • Modern chemical knowledge is based largely on principles that answer the “why” as well as the “howto.” • 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 METALS
Spodumene LiAl(SiO3)2
The Alkali Metals • Discoveries 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. –
Flame Colors
Properties and Trends in Group 1A • The 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 Lithium In 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
Diagonal Relationships The elements in each encircled pair have several similar properties.
Occurrence, Preparation, Use, & Reactions of the Alkali Metals • Sodium 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
Occurrence, Preparation, Use, & Reactions of the Alkali Metals • 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: Na2O2 + 2 KO2 + 2CO2 Na2CO3 + K 2CO3 + 2O2 Z Lithium is used in lightweight batteries of the type found in heart pacemakers, cellular telephones, digital cameras, and portable computers.
Group I Compounds • Halides – NaCl 50 million tons/year in U.S. – Preservative, used on roads, water softener regeneration, feedstock for other chemicals – KCl from natural brines. – Plant fertilizers, feedstock.
Important Compounds of Lithium, Sodium, and Potassium • Lithium 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) + H2O • NaCl 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,
Carbonates • Li2CO3 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
Production and Use Electrolysis: 2 NaCl(l) → 2 Na(l) + Cl2(g) Sodium as a reducing agent: KCl(l) + Na(l) → 2 NaCl(l) + K(g) TiCl4 + 4 Na → Ti + 4 NaCl
Preparation of Sodium Compounds from NaCl The methods of preparation suggested by this diagram are not necessarily the preferred industrial methods.