[238] Rats can survive up to 50% substitution of potassium by rubidium. [232], Due to their similar atomic radii, rubidium and caesium in the body mimic potassium and are taken up similarly. This trend is shown in the figure below: The metals in this series are relatively light— lithium, sodium, and potassium are less dense than water (less than 1 g cm-3). Kauzlarich, Encyclopedia of Inorganic chemistry, 1994, John Wiley & Sons. [195], Lithium Li Atomic Number: 3 Atomic Weight: 6.941 Melting Point: 453.85 KBoiling Point: 1615 KSpecific mass: 0.534 g/cm3 Electronegativity: 0.98, Sodium Na Atomic Number: 11 Atomic Weight: 22.98976928 Melting Point: 371.15 K Boiling Point: 1156 KSpecific mass: 0.97 g/cm3 Electronegativity: 0.96, Potassium K Atomic Number: 19 Atomic Weight: 39.0983 Melting Point: 336.5 K Boiling Point: 1032 KSpecific mass: 0.86 g/cm3 Electronegativity: 0.82, Rubidium Rb Atomic Number: 37 Atomic Weight: 85.4678 Melting Point: 312.79 K Boiling Point: 961 KSpecific mass: 1.53 g/cm3 Electronegativity: 0.82, Caesium Cs Atomic Number: 55 Atomic Weight: 132.9054519 Melting Point: 301.7 K Boiling Point: 944 KSpecific mass: 1.93 g/cm3 Electronegativity: 0.79. Generally, we see that in alkali metals the rate of increase of mass is greater than rate of increase of volume, therefore the density increases down the group. [226] The Dietary Reference Intake for sodium is 1.5 grams per day,[227] but most people in the United States consume more than 2.3 grams per day,[228] the minimum amount that promotes hypertension;[229] this in turn causes 7.6 million premature deaths worldwide. [194] When the only natural isotope francium-223 is specifically required, it is produced as the alpha daughter of actinium-227, itself produced synthetically from the neutron irradiation of natural radium-226, one of the daughters of natural uranium-238. [57] For that reason, caesium atoms are used as the definition of the second. Adloff, Jean-Pierre; Kaufman, George B. Sample exam questions - groups in the periodic table - Edexcel, Home Economics: Food and Nutrition (CCEA). [190][191] The limited applications and the lack of a mineral rich in rubidium limit the production of rubidium compounds to 2 to 4 tonnes per year. [221][222], Sodium and potassium occur in all known biological systems, generally functioning as electrolytes inside and outside cells. They are low enough for the first three (lithium, sodium and potassium) to float on water. Group of highly-reactive chemical elements, Representative reactions of alkali metals, While hydrogen also has this electron configuration, it is not considered an alkali metal as it has very different behaviour owing to the lack of, In the 1869 version of Mendeleev's periodic table, copper and silver were placed in their own group, aligned with hydrogen and. Group II (alkaline earth) metals have a higher density because they have more protons and neutrons and they have smaller atomic radius. and Keiter, R.L. In any given period of the periodic table, the atomic radii of the alkali metals is the largest, and the atomic radius increases as one moves down the group. [236][239] Rubidium (and to a much lesser extent caesium) can function as temporary cures for hypokalemia; while rubidium can adequately physiologically substitute potassium in some systems, caesium is never able to do so. The alkali metals are a group of chemical elements from the s-block of the periodic table with similar properties: they appear silvery and can be cut with a plastic knife. Thus, the order of density is Li K Na Rb Cs Densities are Li - 0.53 g/cc Na - 0.97 g/cc K-0.86 g/cc Rb - 1.53 g/cc Cs - 1.90 g/cc [10]:71 Pure rubidium and caesium metals are produced by reducing their chlorides with calcium metal at 750 °C and low pressure. The group 1 elements are all soft, reactive metals with low melting points. The densities of alkali metals are much lower when compared to other metals. Sodium salts of fatty acids are used as soap. Lithium stearate is a thickener and can be used to make lubricating greases; it is produced from lithium hydroxide, which is also used to absorb carbon dioxide in space capsules and submarines. Potassium hydroxide is a very strong base, and is used to control the pH of various substances. p. 247. [240][241], Caesium compounds are rarely encountered by most people, but most caesium compounds are mildly toxic. [200][201] Being a strong reducing agent, it is often used to reduce many other metals, such as titanium and zirconium, from their chlorides. [10]:70 Lithium chloride is used as a brazing alloy for aluminium parts. For shortcuts to the pages of this section, see the alkali metals. The table shows the melting points of five alkali metals. [212] Some Class D dry powder extinguishers designed for metal fires are effective, depriving the fire of oxygen and cooling the alkali metal. 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