<Tr> <Td_colspan="2"> <Ul> <Li> view </Li> <Li> talk </Li> <Li> </Li> </Ul> references in Wikidata </Td> </Tr> <Ul> <Li> view </Li> <Li> talk </Li> <Li> </Li> </Ul> <P> Potassium is a chemical element with symbol K (from Neo-Latin kalium) and atomic number 19 . It was first isolated from potash, the ashes of plants, from which its name derives . In the periodic table, potassium is one of the alkali metals . All of the alkali metals have a single valence electron in the outer electron shell, which is easily removed to create an ion with a positive charge--a cation, which combines with anions to form salts . Potassium in nature occurs only in ionic salts . Elemental potassium is a soft silvery - white alkali metal that oxidizes rapidly in air and reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction and burning with a lilac - colored flame . It is found dissolved in sea water (which is 0.04% potassium by weight), and is part of many minerals . </P> <P> Potassium is chemically very similar to sodium, the previous element in group 1 of the periodic table . They have a similar first ionization energy, which allows for each atom to give up its sole outer electron . That they are different elements that combine with the same anions to make similar salts was suspected in 1702, and was proven in 1807 using electrolysis . Naturally occurring potassium is composed of three isotopes, of which K is radioactive . Traces of K are found in all potassium, and it is the most common radioisotope in the human body . </P>

What group of the periodic table is potassium in