<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 40 K is radioactive . Traces of 40 K are found in all potassium, and it is the most common radioisotope in the human body . </P> <P> Potassium ions are necessary for the function of all living cells . The transfer of potassium ions through nerve cell membranes is necessary for normal nerve transmission; potassium deficiency and excess can each result in numerous abnormalities, including an abnormal heart rhythm and various electrocardiographic (ECG) abnormalities . Fresh fruits and vegetables are good dietary sources of potassium . The body responds to the influx of dietary potassium, which raises serum potassium levels, with a shift of potassium from outside to inside cells and an increase in potassium excretion by the kidneys . </P> <P> Most industrial applications of potassium exploit the high solubility in water of potassium compounds, such as potassium soaps . Heavy crop production rapidly depletes the soil of potassium, and this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production . </P>

Where is potassium located in the human body