Monatomics, Monoatomics

The relative density of potassium vapour at 1040° (H unity) is between 40 and 45 very nearly corresponding with monoatomic molecules.59 The vapour densities of the alkali metals are somewhat inaccurate because they attack the containing vessels. The value for sodium, between 15 1 and 25 8, also agrees with a monatomic mol. W. Ramsay s experiments on the effect of potassium on the f.p. of mercury show that the alkali metals are possibly univalent in mercurial soln. C. T. Heycock obtained similar results from the effects of lithium, and potassium on the f.p. of sodium and of sodium on the f.p. of cadmium, tin, lead, and bismuth. 

The only chemically stable ion of rabidium is Rb. The most stable monoatomic ion of bromine is Br . Krypton (Kr) is among the least reactive of all elements. Compare the electron configurations of Rb, Br , and Kr. Then predict the most stable monatomic ions of strontium (Sr) and selenium (Se). 

Another problem that is frequently encountered is to know what the appropriate charge can be on the ions under consideration. For monoatomic cations and anions, the common charges are called oxidation numbers, and they can often be identified on a periodic table (see Chapter 4). Polyatomic ions are more challenging and often must be derived from the oxidation numbers of the underlying monatomic components. Knowing some rules to determine the oxidation numbers of elements will allow you to calculate the charge for polyatomic ions. 

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