Transcript Rubidium
Symbol: Rb Atomic number: 37 Atomic mass: 85.4678 Group: Alkali Metal Rubidium is a chemical element in the periodic table that has the symbol Rb and atomic number 37. Rb is a soft, silverywhite metallic element of the alkali metal group Electronic data Thermal data Steric Data Shells: 2,8,18,8,1 Orbitals: [Kr] 5s1 Electronegativity: 0.9, 0.8 1. Ionization potential: 4.1771 eV 2. Ionization potential: 27.28 eV 3. Ionization potential: 40.0 eV Oxidation states: 1 Electrical conductivity: 0.0779 10^6 Melting point: 38.89 °C Boiling point: 686 °C Specific heat: 0.363 J/gK Heat of fusion: 2.192 kJ/mol Heat of vaporization: 72.216 kJ/mol Thermal conductivity: 0.582 W/cmK Atomic radius: 2.98 Å Ionic radius: 1.61 Å () Covalent radius: 2.16 Å Atomic volume: 55.9 cm³/mol Density (293 K): 1.53 g/cm³ Crystal structure: Cubic: Body centered History Rubidium was discovered by the German chemists Robert Bunsen and Gustav Kirchoff in 1861 while analyzing samples of the mineral lepidolite (KLi2Al(Al, Si)3O10(F, OH)2) with a device called a spectroscope. The sample produced a set of deep red spectral lines they had never seen before Bunsen The name rubidium (from the Latin "rubidus" - dark red) was coined for its bright red spectroscopic lines. Kirchoff Occurrence This element is considered to be the 16th most abundant element in the earth's crust. It occurs naturally in the minerals leucite, pollucite, and zinnwaldite, which contains traces of up to 1% of its oxide. Lepidolite contains 1.5% rubidium and this is the commercial source of the element. Some potassium minerals and potassium chlorides also contain the element in commercially significant amounts. One notable source is also in the extensive deposits of pollucite at Bernic Lake, Manitoba. Rubidium metal can be produced by reducing rubidium chloride with calcium among other methods. Isolation Rubidium would not normally be made in the laboratory as it is available commercially. All syntheses require an electrolytic step as it is so difficult to add an electron to the poorly electronegative rubidium ion Rb+. Rubidium is not made by the same method as sodium as might have been expected. This is because the rubidium metal, once formed by electrolysis of liquid rubidium chloride (RbCl), is too soluble in the molten salt. cathode: Rb+(l) + e- Rb (l) anode: Cl-(l) 1/2Cl2 (g) + e- Instead, it is made by the reaction of metallic sodium with hot molten rubidium chloride. Na + RbCl Rb + NaCl This is an equilibrium reaction and under these conditions the rubidium is highly volatile and removed from the system in a form relatively free from sodium impurities, allowing the reaction to proceed. Chemical reactions of the elements Reaction of rubidium with air If rubidium is burned in air, the result is mainly formation of dark brown rubidium superoxide, RbO2. Rb(s) + O2(g) RbO2(s) Reaction of rubidium with water Rubidium metal reacts very rapidly with water to form a colourless solution of rubidium hydroxide (RbOH) and hydrogen gas (H2). The reaction is very exothermic. 2 Rb(s) + 2H2O 2RbOH(aq) + H2(g) Chemical reactions of the elements Reaction of rubidium with the halogens Rubidium metal reacts vigorously with all the halogens to form rubidium halides. 2Rb(s) + F2(g) RbF(s) 2Rb(s) + Cl2(g) RbCl(s) 2Rb(s) + Br2(g) RbBr(s) 2Rb(s) + I2(g) RbI(s) Reaction of rubidium with acids Rubidium metal dissolves readily in dilute sulphuric acid to form solutions containing the aquated Rb(I) ion together with hydrogen gas, H2. 2Rb(s) + H2SO4(aq) 2Rb+(aq) + SO42-(aq) + H2(g) Binary Compounds Hydrides HRb: rubidium (I) hydride Fluorides RbF: rubidium (I) fluoride Chlorides RbCl: rubidium (I) chloride Bromides RbBr: rubidium (I) bromide Iodides RbI: rubidium (I) iodide Sulfides Rb2S: rubidium (I) sulphide Selenides Rb2Se: rubidium (I) selenide Tellurides Rb2Te: rubidium (I) telluride Oxides Rb2O: rubidium (I) oxide RbO2: rubidium (I) superoxide Rb2O2: rubidium (I) peroxide Applications Rubidium is easily ionized, and so has possible use in "ion engines" for space vehicles As a getter in vacuum tubes. As a photocell component. In the making of special glasses. Rubidium compounds are sometimes used in fireworks to give them a purple color.