![]() The golden colour of caesium comes from the decreasing frequency of light required to excite electrons of the alkali metals as the group is descended. A few amalgams have been studied: CsHgĢ is black with a purple metallic lustre, while CsHg is golden-coloured, also with a metallic lustre. It mixes with all the other alkali metals (except lithium) the alloy with a molar distribution of 41% caesium, 47% potassium, and 12% sodium has the lowest melting point of any known metal alloy, at −78 ☌ (−108 ☏). It forms well-defined intermetallic compounds with antimony, gallium, indium, and thorium, which are photosensitive. At temperatures below 650 ☌ (1,202 ☏), it does not alloy with cobalt, iron, molybdenum, nickel, platinum, tantalum, or tungsten. Its compounds burn with a blue or violet colour.Ĭaesium crystals (golden) compared to rubidium crystals (silvery)Ĭaesium forms alloys with the other alkali metals, gold, and mercury ( amalgams). In addition, the metal has a rather low boiling point, 641 ☌ (1,186 ☏), the lowest of all metals other than mercury. Mercury is the only stable elemental metal with a known melting point lower than caesium. It has a melting point of 28.5 ☌ (83.3 ☏), making it one of the few elemental metals that are liquid near room temperature. When in the presence of mineral oil (where it is best kept during transport), it loses its metallic lustre and takes on a duller, grey appearance. It is a very ductile, pale metal, which darkens in the presence of trace amounts of oxygen. Of all elements that are solid at room temperature, caesium is the softest: it has a hardness of 0.2 Mohs. Nonradioactive caesium compounds are only mildly toxic, but the pure metal's tendency to react explosively with water means that caesium is considered a hazardous material, and the radioisotopes present a significant health and environmental hazard.Ĭharacteristics Physical properties High-purity caesium-133 stored in argon. The radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology. Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids, but it has a range of applications in the production of electricity, in electronics, and in chemistry. Since then, caesium has been widely used in highly accurate atomic clocks. In 1967, acting on Einstein's proof that the speed of light is the most-constant dimension in the universe, the International System of Units used two specific wave counts from an emission spectrum of caesium-133 to co-define the second and the metre. The first small-scale applications for caesium were as a " getter" in vacuum tubes and in photoelectric cells. The German chemist Robert Bunsen and physicist Gustav Kirchhoff discovered caesium in 1860 by the newly developed method of flame spectroscopy. It has the largest atomic radius of all elements whose radii have been measured or calculated, at about 260 picometers. Caesium-137, a fission product, is extracted from waste produced by nuclear reactors. It has only one stable isotope, caesium-133. It is the least electronegative element, with a value of 0.79 on the Pauling scale. It is pyrophoric and reacts with water even at −116 ☌ (−177 ☏). Caesium has physical and chemical properties similar to those of rubidium and potassium. It is a soft, silvery-golden alkali metal with a melting point of 28.5 ☌ (83.3 ☏), which makes it one of only five elemental metals that are liquid at or near room temperature. When carbon dioxide dissolves in water, it forms a solution, which turns blue litmus paper red, telling us that non-metal oxides are acidic.Caesium ( IUPAC spelling cesium in American English) is a chemical element with the symbol Cs and atomic number 55. When burnt in oxygen, the carbon in this charcoal reacts to form carbon dioxide. Some non-metals can also react with oxygen in an oxidation reaction. So this shows us that metal oxides are bases, when added to water. When we add water the magnesium oxide dissolves to form a solution that turns red litmus paper blue, telling us it is alkaline also called a base. When you burn magnesium in the air in the same way that the iron did, the magnesium reacts with oxygen to produce magnesium oxide. ![]() The iron oxide is no longer a pure metal, it is a dull, dark-coloured, metal compound. This is because when the iron is heated, oxidation takes place. When a sparkler has finished burning, you’ll notice that the iron pieces on the rod have changed colour. When you burn the iron it reacts with oxygen to make iron oxide, creating the sparks we see. The burning metals are reacting with oxygen in the air and producing metal oxides. The sparks in fireworks are made by burning different metals. When substances combine with oxygen the process is called oxidation and the compounds made are called oxides.
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