Samples Containing Lithium, Sodium, Potassium, Rubidium or Cesium

The Metals

The alkali metals, lithium (Li), sodium (Na), potassium (K), rubidium (Rb) and cesium (Cs), are all extremely light in weight, compressible, and relatively, very soft. Lithium is the hardest of the alkali metals with a hardness of 0.6 on Mohs' scale. Freshly cut surfaces of the alkali metals show a silvery white luster, which tarnishes quickly and becomes dull in air.

All of the alkali elements are univalent (+1), electropositive, and form strong bases. They react with and decompose water, the reaction increasing in vigor with atomic number. Potassium, rubidium and cesium ignite when placed on water. The resulting alkali hydroxides are very soluble in water and are essentially completely dissociated in aqueous solution. Typically, analysts prefer to introduce neutral or acidic solutions of these elements to avoid attack of the glass and quartz introduction components of their introduction systems. The use of nitric acid is most common in the neutralization of the hydroxides but HCl will work equally well. Other acids are less commonly used for matrix adjustment and perchloric acid is avoided due to the relative insolubility of its salts with K, Rb, and Cs.

The alkali group elements have a chemistry that is more similar than any other group in the Periodic Table. For this reason, the preparation chemistry will be presented as a group rather than for each individual element.

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