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Group 1: Alkali metals Reaction of sodium (Na) and water Reaction of potassium (K) in water. The alkali metals (Li, Na, K, Rb, Cs, and Fr) are the most reactive metals in the periodic table - they all react vigorously or even explosively with cold water, resulting in the displacement of hydrogen.
The order of reactivity, as shown by the vigour of the reaction with water or the speed at which the metal surface tarnishes in air, appears to be Cs > K > Na > Li > alkaline earth metals, i.e., alkali metals > alkaline earth metals, the same as the reverse order of the (gas-phase) ionization energies.
Metal aqua ions are often involved in the formation of complexes. The reaction may be written as pM x+ (aq) + qL y− → [M p L q] (px-qy)+ In reality this is a substitution reaction in which one or more water molecules from the first hydration shell of the metal ion are replaced by ligands, L. The complex is described as an inner-sphere complex.
In fact, the rate of reaction of alkali metals (as evidenced by their reaction with water for example) is a function not only of position within the group but also of particle size. Hydrogen does not react with oxygen—even though the equilibrium constant is very large—unless a flame initiates the radical reaction, which leads to an explosion.
Solvated electrons are involved in the reaction of alkali metals with water, even though the solvated electron has only a fleeting existence. [10] Below pH = 9.6 the hydrated electron reacts with the hydronium ion giving atomic hydrogen, which in turn can react with the hydrated electron giving hydroxide ion and usual molecular hydrogen H 2. [11]
This secondary hydrogen gas explosion produces the visible flame above the bowl of water, lake or other body of water, not the initial reaction of the metal with water (which tends to happen mostly under water). [74] The alkali metal hydroxides are the most basic known hydroxides. [10]: 87 Recent research has suggested that the explosive ...
This reaction occurs quantitatively with salts of the alkali-metals at low to moderate concentrations. [citation needed] With salts of divalent metal ions, the aqua-ion will be subject to a dissociation reaction, known as hydrolysis, a name derived from Greek words for water splitting. The first step in this process can be written as [citation ...
Rubidium, being denser than potassium, sinks in water, reacting violently; caesium explodes on contact with water. [18] However, the reaction rates of all alkali metals depend upon surface area of metal in contact with water, with small metal droplets giving explosive rates. [19] Rubidium has also been reported to ignite spontaneously in air. [11]