Potassium
Potassium is a soft, silvery alkali metal with atomic number 19. Its ions are essential to living cells, while the metal reacts vigorously with water.
Alkali metal: An element in Group 1 of the periodic table, characterized by one outer electron and high chemical reactivity. Potassium belongs to this group, whose shared electron structure explains its characteristic reactions.
Atomic number: The number of protons in an atom’s nucleus, which determines the identity of its element. Potassium’s 19 protons define it as element 19.
Potash: A general name for potassium-rich compounds used chiefly as fertilizers and in some industrial processes. Potash supplies potassium to crops in forms that are safer to handle than the metal.
Sodium: A soft, reactive alkali metal with atomic number 11, whose ions are abundant outside animal cells. Sodium and potassium have complementary concentration gradients across cell membranes.
Resting potential: The electrical voltage across a cell membrane when the cell is not producing an action potential. Potassium leakage across membranes helps establish the resting voltage of many cells.
Potassium ion: A potassium atom that has lost one electron, forming the positively charged ion K⁺. Most biological potassium occurs as K⁺ rather than as the reactive metal.
Electron shell: A group of atomic orbitals with similar energies that electrons occupy around an atomic nucleus. Potassium’s outermost electron shell helps account for its reactivity.
Potassium chloride: An ionic compound of potassium and chlorine, commonly used in fertilizers and as a salt substitute. It is a major source of potassium in agriculture and a dietary mineral supplement.
Rubidium: A soft, highly reactive alkali metal with atomic number 37, located below potassium in Group 1. As potassium’s heavier group neighbor, rubidium shares many chemical properties.
Action potential: A rapid, temporary change in a cell’s membrane voltage that propagates along excitable cells. Potassium movement helps repolarize membranes after an action potential.