PeriodicElementTable.com
19K39.0983
Alkali metal

Potassium

Potassium is a soft, silvery alkali metal so reactive that it has to be stored away from air and water to keep it from corroding or igniting. Far from being just a laboratory curiosity, its ions are essential to life, driving the electrical signals that let nerves fire and muscles contract.

Group · Period
1 · 4
At room temp
solid
Melts at
336.53 K
Density
0.89 g/cm³
Discovered
1807

Uses

Most potassium mined and processed worldwide ends up in fertilizer, usually as potassium chloride or potassium sulfate, because plants need a steady supply of potassium ions to grow and are quickly depleted from farmed soil. Beyond agriculture, potassium compounds are used in soap and glassmaking, and potassium hydroxide is an ingredient in some alkaline batteries and industrial cleaning products.

In the body, potassium is just as essential as it is on the farm: it’s the main positive ion inside cells, and the balance between potassium and sodium across cell membranes is what allows nerve impulses to travel and heart and skeletal muscles to contract properly.

History

Humphry Davy first isolated metallic potassium in 1807 by passing an electric current through molten potassium hydroxide, watching small globules of the new metal form and immediately catch fire on contact with air. It was the first metal ever obtained by electrolysis, a method Davy went on to use for isolating several other reactive elements. He named it potassium after potash, the traditional source of potassium compounds long used by soap makers and glassmakers, even though the pure metal itself had never been seen before his experiment.

Fun facts

  • Dropped into water, potassium reacts violently enough to ignite the hydrogen gas it releases, burning with a distinctive lilac flame.
  • Potassium was the first metal ever isolated by electrolysis, a technique Humphry Davy pioneered specifically to obtain it.
  • Potassium ions are essential electrolytes in the human body, and a healthy diet needs a steady supply from foods like bananas, potatoes, and leafy greens.

Frequently asked questions

Why does potassium react so violently with water?

Like other alkali metals, potassium has a single loosely held outer electron that it gives up easily, and it does so almost instantly when it touches water. The reaction generates hydrogen gas and enough heat to ignite that hydrogen on the spot, which is why potassium is stored under oil, away from any moisture.

Is the potassium in bananas the same as the metal that explodes in water?

Chemically they're the same element, but the form matters enormously. Bananas contain potassium as dissolved ions bound up in salts and other compounds, which are stable and safe to eat. Pure metallic potassium, with its single free outer electron ready to react, is a completely different, highly reactive state of the same element.

Why does potassium's symbol, K, not match its name?

The symbol comes from "kalium," the Latin name derived from an Arabic word for the ashes of certain plants, which were historically used as a source of potassium compounds. English speakers settled on "potassium" — from "potash," the pot-leached ashes it was traditionally extracted from — while the symbol kept its older Latin root.

Compounds

7 notable compounds containing K

  • KBrsalt

    Potassium bromide

    A colorless crystalline salt transparent to infrared light, which makes it a standard window and pellet material for infrared spectroscopy.

    Used for: Sample windows/pellets in IR spectroscopy; historically an anticonvulsant

  • KClsalt

    Potassium chloride

    An ionic salt closely related to table salt, forming colorless cubic crystals that dissolve readily in water. It occurs naturally as the mineral sylvite.

    Used for: Potassium fertilizer, salt substitute, and IV saline solutions

  • K2Cr2O7salt

    Potassium dichromate

    A bright orange crystalline salt and one of the most recognizable chromium(VI) compounds, prized in classical chemistry for its strong, reliable oxidizing power in acidic solution.

    Used for: Oxidizing agent in redox titrations and historically in leather tanning

  • KOHbase

    Potassium hydroxide

    A strong, highly caustic alkali that dissolves readily in water and absorbs moisture from air. It's the potassium counterpart to sodium hydroxide (lye).

    Used for: Manufacturing liquid soaps, batteries, and biodiesel

  • KIsalt

    Potassium iodide

    A simple ionic salt that supplies iodide ions, commonly added to table salt to prevent iodine deficiency. It also protects the thyroid gland by saturating it with stable iodine.

    Used for: Iodized table salt and thyroid-blocking tablets after radiation exposure

  • KNO3mineral

    Potassium nitrate

    Also known as saltpeter, this ionic salt forms colorless crystals and acts as a strong oxidizer when heated. It occurs naturally as efflorescent deposits in soil and caves.

    Used for: Traditional ingredient in gunpowder and a common fertilizer

  • KMnO4industrial

    Potassium permanganate

    A deep purple crystalline salt that acts as a strong oxidizing agent, staining almost anything it touches. Its color comes from manganese sitting in its +7 oxidation state.

    Used for: Water treatment, wound disinfection, and wilderness fire-starting

Isotopes

25 known isotopes

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IsotopeNatural abundanceHalf-lifeDecay modeMass excessBinding energy / nucleonDecay width
K-39 stable 93.2581% Stable — -33,807.2 keV 8,557.03 keV —
K-40 0.0117% 1.248E+9 Y Beta-minus decay (89.28%), Electron capture / beta-plus decay (10.72%) -33,535.5 keV 8,538.09 keV 1.16 × 10-32 eV
K-41 stable 6.7302% Stable — -35,559.55 keV 8,576.07 keV —
Show all 25 isotopes
K-31 — 10 ps Proton emission (100%) 34,260 keV 6,487 keV 4.56 × 10-5 eV
K-33 — 25 ns Proton emission 7,540 keV 7,392 keV 1.82 × 10-8 eV
K-34 — 25 ns Proton emission -1,220 keV 7,670 keV 1.82 × 10-8 eV
K-35 — 178 ms Electron capture / beta-plus decay (100%), ECP (0.37%) -11,172.89 keV 7,965.84 keV 2.56 × 10-15 eV
K-36 — 341 ms Electron capture / beta-plus decay (100%), ECP (0.048%), ECA (0.0034%) -17,417.18 keV 8,142.22 keV 1.34 × 10-15 eV
K-37 — 1.225 s Electron capture / beta-plus decay (100%) -24,800.2 keV 8,339.85 keV 3.72 × 10-16 eV
K-38 — 7.651 m Electron capture / beta-plus decay (100%) -28,800.76 keV 8,438.06 keV 9.94 × 10-19 eV
K-42 — 12.355 h Beta-minus decay (100%) -35,022.03 keV 8,551.26 keV 1.03 × 10-20 eV
K-43 — 22.3 h Beta-minus decay (100%) -36,575.39 keV 8,576.22 keV 5.68 × 10-21 eV
K-44 — 22.13 m Beta-minus decay (100%) -35,781.5 keV 8,546.7 keV 3.44 × 10-19 eV
K-45 — 17.81 m Beta-minus decay (100%) -36,615.64 keV 8,554.67 keV 4.27 × 10-19 eV
K-46 — 105 s Beta-minus decay (100%) -35,413.93 keV 8,518.04 keV 4.35 × 10-18 eV
K-47 — 17.50 s Beta-minus decay (100%) -35,711.98 keV 8,514.88 keV 2.61 × 10-17 eV
K-48 — 6.8 s Beta-minus decay (100%), Beta-minus, neutron emission (1.14%) -32,284.48 keV 8,434.23 keV 6.71 × 10-17 eV
K-49 — 1.26 s Beta-minus decay (100%), Beta-minus, neutron emission (86%) -29,611.5 keV 8,372.28 keV 3.62 × 10-16 eV
K-50 — 472 ms Beta-minus decay (100%), Beta-minus, neutron emission (29%), B-2N -25,727.85 keV 8,288.58 keV 9.67 × 10-16 eV
K-51 — 365 ms Beta-minus decay (100%), Beta-minus, neutron emission (65%) -22,515.46 keV 8,221.34 keV 1.25 × 10-15 eV
K-52 — 110 ms Beta-minus decay (100%), Beta-minus, neutron emission (74%), B-2N (2.3%) -17,137.63 keV 8,115.03 keV 4.15 × 10-15 eV
K-53 — 30 ms Beta-minus decay (100%), Beta-minus, neutron emission (67%), B-2N (17%) -12,295.72 keV 8,022.85 keV 1.52 × 10-14 eV
K-54 — 10 ms Beta-minus decay (100%), B-2N, Beta-minus, neutron emission -5,150 keV 7,891 keV 4.56 × 10-14 eV
K-55 — — Beta-minus decay (100%), Beta-minus, neutron emission, B-4N 470 keV 7,792 keV —
K-56 — — Beta-minus decay (100%), Beta-minus, neutron emission, B-2N 7,980 keV 7,663 keV —