Chemical reactions of the elements

Reaction of caesium with air

Caesium (cesium in USA) is very soft and easily cut. The resulting surface is bright and shiny. However, this surface soon tarnishes because of reaction with oxygen and moisture from the air. If caesium is burned in air, the result is mainly formation of orange caesium superoxide, CsO2.

Cs(s) + O2(g) → CsO2(s)

Reaction of caesium with water

Caesium (cesium in USA) metal reacts rapidly with water to form a colourless solution of caesium hydroxide (CsOH) and hydrogen gas (H2). The resulting solution is basic because of the dissolved hydroxide. The reaction is very exothermic. The reaction is so fast that if the reaction is carried out in a glass vessel, the glass container will shatter. Although not known for certain, the reaction is probably slower than that of francium (immediately below caesium in the periodic table). The reaction is faster than that of rubidium (immediately above caesium in the periodic table).

2Cs(s) + 2H2O → 2CsOH(aq) + H2(g)

Reaction of caesium with the halogens

Caesium (cesium in USA) metal reacts vigorously with all the halogens to form caesium halides. So, it reacts with fluorine, F2, chlorine, Cl2, bromine, I2, and iodine, I2, to form respectively caesium(I) bromide, CsF, caesium(I) chloride, CsCl, caesium(I) bromide, CsBr, and caesium(I) iodide, CsI.

2Cs(s) + F2(g) → CsF(s)

2Cs(s) + Cl2(g) → CsCl(s)

2Cs(s) + Br2(g) → CsBr(s)

2Cs(s) + I2(g) → CsI(s)

Reaction of caesium with acids

Caesium (cesium in USA) metal dissolves readily in dilute sulphuric acid to form solutions containing the aquated Cs(I) ion together with hydrogen gas, H2.

2Cs(s) + H2SO4(aq) → 2Cs+(aq) + SO42-(aq) + H2(g)

Reaction of caesium with bases

Caesium (cesium in USA) metal reacts rapidly with water to form a colourless basic solution of caesium hydroxide (CsOH) and hydrogen gas (H2). The reaction continues even when the solution becomes basic. The resulting solution is basic because of the dissolved hydroxide. The reaction is very exothermic. The reaction is so fast that if the reaction is carried out in a glass vessel, the glass container will shatter. Although not known for certain, the reaction is probably slower than that of francium (immediately below caesium in the periodic table). The reaction is faster than that of rubidium (immediately above caesium in the periodic table). As thereaction continues, the concentration of base increases.

2Cs(s) + 2H2O → 2CsOH(aq) + H2(g)

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caesium atomic number