Potassium

Potassium is a soft, silvery-white metal in group 1 of the periodic table. It is so soft it can be cut with a knife, and a freshly cut surface tarnishes within seconds in air. Like all alkali metals it has a single valence electron, which it loses eagerly to form the +1 ion — reacting violently with water and igniting in moist air, so samples are stored under oil.

Beyond the laboratory, potassium is essential to life. Human nerve impulses and muscle contractions depend on sodium-potassium pumps in cell membranes, and plants need large amounts of it for growth, which is why potassium compounds are a major fertilizer ingredient. Industrially it appears in soaps, glass, and heat-transfer alloys.

Key facts

Occurrence

Potassium never occurs free in nature because of its extreme reactivity. It ranks as the seventh most abundant element in Earth's crust, found in minerals such as sylvite (potassium chloride) and feldspar, and dissolved in seawater. Plants concentrate it from soil, which is why bananas and potatoes are known sources.

Applications

• Fertilizers supply potassium as a primary plant nutrient (potash)

• Soaps and detergents made with potassium hydroxide are softer than sodium-based ones

• Glass manufacturing uses potassium carbonate for specialty optical glass

• Potassium nitrate serves in curing salts and historical gunpowder

• Liquid sodium-potassium alloy transfers heat in nuclear reactors

Common compounds

• potassium chloride
• potassium nitrate
• potassium hydroxide
• potassium carbonate
• potassium permanganate
• potassium bromide

Data source: IUPAC standard atomic weights 2021

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