Alkali Metal

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alkali metal

[′al·kə‚lī ‚med·əl]
(chemistry)
Any of the elements of group I in the periodic table: lithium, sodium, potassium, rubidium, cesium, and francium.

Alkali Metal

 

any one of several chemical elements of the major subgroup of Group I of Mendeleev’s periodic system of the elements: lithium, sodium, potassium, rubidium, cesium, and francium. The subgroup’s name is derived from the hydroxides of the alkali metals, called caustic alkalies. The atoms of alkali metals have one s electron in their outer shell and, with the exception of lithium, two 5 electrons and six p electrons in the next to the last shell. The alkali metals always exhibit an oxidation number of +1 in their compounds. They are very reactive chemically. They are oxidized rapidly by atmospheric oxygen and react vigorously with water to form alkalies, MeOH (where Me is a metal). Their reactivity increases from lithium to francium. (See alsoLITHIUM; SODIUM; POTASSIUM; RUBIDIUM; CESIUM; and FRANCIUM.)

References in periodicals archive ?
For a testing time suitably long to approach equilibrium conditions, [C.sub.t] maybe taken equal to [C.sub.eq], the latter being the alkaline metal concentration at equilibrium in the leaching solution.
Assuming that equilibrium conditions are approached and there is no binding of alkaline metals by the solid phase of the cement paste, the following balance equation can be written, with reference to the alkaline metal under consideration:
The first member of this equation represents the amount of the alkaline metal (sodium or potassium) released or accumulated per unit weight of the cement paste and corresponds to [M.sub.r], as defined by (1).
The intercept of the straight line with the x-axis stands for [C.sup.0.sub.p], that is, the concentration of the alkaline metal in the pore solution of the cementitious matrix before the leaching test.
Therefore, the deviation from linearity can be considered as an index of metal binding by the cementitious matrix and, accordingly, the extent of such a deviation was used to calculate the amount of the alkaline metal, sodium or potassium, bound by long-term hydrated CEM IV/B (P) or CEM IV/B (V) pastes.
Group I contains alkaline metals having very strong chemical activity, but simultaneously the sub-Group "b" contains copper, silver and gold which have not these properties but possess excellent electric conductivity.
It is shown that method of electron beam evaporation in vacuum of stainless steel and salts of the alkaline metal halogenides with different melting temperatures (chloral sodium and chloral potassium) allows producing in joint deposition of their vapor flows porous condensates, temperature dependence of porosity of which is of nonmonotonous character with maximum in the area of 0.6 [T.sub.m] temperature with characteristic formation of elongated pores of open type.
Taking into account the results obtained, it was assumed that if to use as a porophore halogenides of alkaline metals with different values of the melting point, it will be possible to change temperature conditions, at which condensates with maximal porosity will be formed.

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