- Potassium (K) is a soft, silvery-white alkali metal with atomic number 19, positioned in Group 1 of the periodic table.
- It has one valence electron in its outermost shell, making it highly reactive and eager to lose that electron to form K⁺ cations. Its atomic structure consists of nineteen protons, typically twenty neutrons, and nineteen electrons arranged in four shells (two in the first shell, eight in the second, eight in the third, and one in the fourth).
- Potassium has three naturally occurring isotopes: potassium-39 (³⁹K), the most abundant at about 93.2581%; potassium-41 (⁴¹K), about 6.7302%; and potassium-40 (⁴⁰K), about 0.0117%, which is radioactive with a half-life of about 1.25 billion years and decays into either calcium-40 or argon-40.
- Potassium is the seventh most abundant element in Earth’s crust and occurs naturally only in ionic compounds due to its high reactivity. It is widely distributed in minerals such as sylvite (KCl), carnallite (KMgCl₃·6H₂O), and orthoclase feldspar (KAlSi₃O₈). Large deposits of potassium salts are found in evaporite formations, where ancient seas have dried up. Industrial extraction of potassium compounds often involves mining potash ores, which are processed to yield potassium chloride, potassium sulfate, and other salts.
- The element was first isolated in 1807 by Sir Humphry Davy, who obtained it through the electrolysis of molten potassium hydroxide (KOH). Potassium was the first metal to be isolated by electrolysis, and its name derives from the English word “potash” (pot ashes), as potassium compounds were historically obtained from wood ash. Its symbol “K” comes from the Latin kalium, which itself traces back to the Arabic al-qalyah meaning “alkali.”
- Potassium is essential for all known life forms. In biology, potassium ions play a critical role in maintaining osmotic balance, nerve impulse transmission, and muscle contraction. The sodium–potassium pump, an active transport mechanism in cell membranes, maintains the concentration gradients of sodium and potassium, vital for cellular function. Plants require potassium for enzyme activation, photosynthesis, and water regulation, making potassium fertilizers a key component in agriculture.
- Industrially, potassium compounds have diverse applications. Potassium hydroxide is used in soap making, batteries, and chemical synthesis. Potassium nitrate (KNO₃) is a major component of fertilizers, explosives, and fireworks. Potassium carbonate is used in glass production and as a buffering agent. Metallic potassium itself is used in some specialized chemical processes, though its high reactivity requires handling under inert atmospheres like argon or mineral oil.
- Chemically, potassium is one of the most reactive metals, reacting vigorously with water to produce potassium hydroxide and hydrogen gas, often igniting the hydrogen. It also reacts with oxygen to form potassium oxides and with halogens to produce potassium halides. Potassium’s reactivity increases as one moves down Group 1, and it is more reactive than sodium but less so than rubidium or cesium.
- Biologically and environmentally, potassium is generally non-toxic in normal dietary amounts and is vital to health. However, excessive potassium in the blood (hyperkalemia) can disrupt heart rhythms and be life-threatening. Industrially, potassium compounds are generally safe when handled correctly, though metallic potassium poses fire and explosion hazards.
