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Beryllium is the single exception to both rules, due to its low atomic number. [89] All of the alkali metals except lithium and caesium have at least one naturally occurring radioisotope: sodium-22 and sodium-24 are trace radioisotopes produced cosmogenically, [90] potassium-40 and rubidium-87 have very long half-lives and thus occur naturally ...
Potassium is the eighth or ninth most common element by mass (0.2%) in the human body, so that a 60 kg adult contains a total of about 120 g of potassium. [84] The body has about as much potassium as sulfur and chlorine, and only calcium and phosphorus are more abundant (with the exception of the ubiquitous CHON elements). [ 85 ]
Bulk sodium is usually stored in oil or an inert gas. Sodium metal can be easily cut with a knife. It is a good conductor of electricity and heat. Due to having low atomic mass and large atomic radius, sodium is third-least dense of all elemental metals and is one of only three metals that can float on water, the other two being lithium and ...
Rubidium is also used as an ingredient in special types of glass, in the production of superoxide by burning in oxygen, in the study of potassium ion channels in biology, and as the vapor in atomic magnetometers. [59] In particular, 87 Rb is used with other alkali metals in the development of spin-exchange relaxation-free (SERF) magnetometers. [59]
Lithium metal is soft enough to be cut with a knife. It is silvery-white. In air it oxidizes to lithium oxide. [10] Its melting point of 180.50 °C (453.65 K; 356.90 °F) [13] and its boiling point of 1,342 °C (1,615 K; 2,448 °F) [13] are each the highest of all the alkali metals while its density of 0.534 g/cm 3 is the lowest.
All but the noble gas argon are essential to basic geology and biology. Sodium (Na) is an alkali metal. It is present in Earth's oceans in large quantities in the form of sodium chloride (table salt). Magnesium (Mg) is an alkaline earth metal. Magnesium ions are found in chlorophyll. Aluminium (Al) is a post-transition metal.
[4] [12] Its density of 1.526 g/cm 3 (at 20 °C) [4] is the lowest in its group. [10] Calcium is harder than lead but can be cut with a knife with effort. While calcium is a poorer conductor of electricity than copper or aluminium by volume, it is a better conductor by mass than both due to its very low density. [13]
A chemical element, often simply called an element, is a type of atom which has a specific number of protons in its atomic nucleus (i.e., a specific atomic number, or Z). [ 1 ] The definitive visualisation of all 118 elements is the periodic table of the elements , whose history along the principles of the periodic law was one of the founding ...