Electropositive elements attack

Bromine has a lower electron affinity and electrode potential than chlorine but is still a very reactive element. It combines violently with alkali metals and reacts spontaneously with phosphorus, arsenic and antimony. When heated it reacts with many other elements, including gold, but it does not attack platinum, and silver forms a protective film of silver bromide. Because of the strong oxidising properties, bromine, like fluorine and chlorine, tends to form compounds with the electropositive element in a high oxidation state. 

All the metals are very electropositive and attacked by water vapor with production of hydrogen. They are slowly oxidized in air and at higher temperatures in the form of small chips, they are pyrophoric. The oxides, nitrides, and halides are produced most easily by beating the metals in the appropriate elemental gas. The fluorides are among the most important solid actinide compounds since they are the starting material for the production of the metals. The volatile hexafluoride of uranium is used in isotopic ouichment (Ch. 2). The preparation and properties of U and Th is described in 5.4 — 5.5. Actinide chemistry is also discussed in 21.5 and 22.6. 

The organic derivatives of the most electropositive elements of Group II—Ca, Sr, Ba—have been little studied, and only a very limited amount of reliable information is available. Organic derivatives of calcium appear to resemble somewhat those of lithium, for example, in respect of attack on ethers and on olefins. 

The standard reduction potential for Be2+ is the least negative of the elements in the group and by the same token beryllium is the least electropositive and has the greatest tendency to form covalent bonds. The bulk metal is relatively inert at room temperature and is not attacked by air or water at high temperatures. Beryllium powder is somewhat more reactive. The metal is passivated by cold concentrated nitric acid but dissolves in both dilute acid and alkaline solutions with the evolution of dihydrogen. The metal reacts with halogens at 600°C to form the corresponding dihalides. 

Aqueous solutions of alkali hydroxides do not attack cadmium. Cadmium replaces elements that are less electropositive in the activity series from their salt solutions. The standard electrode potential ... 

One way to look at this process is to say that the elements H and Cl added to the 7t-bond, so it can be called an addition reaction. In reality, the alkene reacts as a Brpnsted-Lowry base with the strong acid to form the C-H bond and a carbocation intermediate. In a second chemical step, the chloride cormter-ion is a nucleophile that attacks the electropositive carbon of the carbocation to form a C-Cl bond. The conversion of cyclopentene to 2 and then to 3 constitutes the mechanism of this reaction, which is the step-by-step chemical sequence of reactions that transforms cyclopentene to chlorocyclopentene. The mechanism of this reaction, as described in Chapter 7 (Section 7.8), is a two-step process in which cyclopentene reacts with HCl to give carbocation 2, which reacts with chloride ion in a second chemical step to give 3. 

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