Potassium is the 19th element of the periodic table. You’ll find this element in bananas, some types of soap, and fertilizer. These potassium facts contain chemical and physical data along with general information and history.
Basic Potassium Facts
Atomic Number: 19
Element Symbol: K
Element Family: Alkali Metal
Atomic Mass: 39.0983(1)
Electron Configuration: [Ar]4s1
Full: 1s22s22p63s23p64s1 (full)
Discovery: Sir Humphry Davy in 1807
Davy is well known for his electrolysis experiments. He would place his instrument in samples of various common chemicals and observe what collects at the electrodes. He isolated pure potassium metal from potash (potassium hydroxide).
Name Origin: Potassium was named from its source: potash. Potash was formed from wood ashes soaked in water.
Element Symbol Origin: The K symbol for potassium comes from the Latin name for potash, kalium. German and Scandinavian chemists used the name kalium for potassium in their texts and journals.
Natural potassium is comprised of three isotopes: 39K, 40K and 41K.
Two stable and twenty two radioactive isotopes exist ranging from 32K to 56K.
Potassium-39 is a stable isotope containing 20 neutrons. 93.2581% of natural potassium is potassium-39.
Potassium-40 is a radioactive isotope containing 21 neutrons. Most of the time, potassium-40 decays by β- decay into 40Ca, but it can also decay β+ decay or electron capture into 40Ar with a half-life of 1.2 billion years. Potassium-40 accounts for 0.117% of natural potassium.
Potassium-41 is a stable isotope containing 22 neutrons. 6.7302% of natural potassium is potassium-39.
Density: 0.89 g/cm3
Melting Point: 336.7 K (63.5 °C, 146.3 °F)
Boiling Point: 1032 K (759 °C, 1398 °F)
Critical Point: 2223 K at 16 MPa
State at 20ºC: Solid
Heat of Fusion: 2.33 kJ/mol
Heat of Vaporization: 76.9 kJ/mol
Molar Heat Capacity: 29.6 J/mol·K
Atomic Radius: 2.27 Å (empirical)
Covalent Radius: 2.03 Å
Van der Waals Radius: 2.75 Å
Electron Affinity: 48.385 kJ/mol
1st Ionization Energy: 418.81 kJ/mol
2nd Ionization Energy: 3051.83 kJ/mol
3rd Ionization Energy: 4419.607 kJ/mol
4th Ionization Energy: 5876.92 kJ/mol
5th Ionization Energy: 7975.48 kJ/mol
6th Ionization Energy: 9590.6 kJ/mol
7th Ionization Energy: 11995.347 kJ/mol
8th Ionization Energy: 13841.79 kJ/mol
Oxidation States: +1 (common), -2 (uncommon)
Fun Potassium Facts
- Potassium is a shiny, lustrous metal at room temperature. When exposed to air, an oxidizing layer forms quickly, turning its appearance to a dull gray.
- Potassium vigorously reacts with water to form hydrogen gas. This gas can ignite from the energy released from the reaction, giving the impression the potassium burns in water.
- Potassium was the first metal to be discovered by electrolysis.
- Potassium has a low density for a metal. Pure potassium metal will float on water.
- Potassium burns with a bright red in a flame test. When in water, the flame takes on a lilac colored hue.
- Potassium is the seventh most abundant element in the human body.
- Potassium is the seventh most abundant element in the Earth’s crust, accounting for 4.2% by mass.
- The largest industrial use of potassium is for fertilizer.
- Potassium is used in soaps, gunpowder, bleaching agents and glass making.
- Potassium-40 is used much like carbon-14 as a radioactive dating marker. K-40 is used to determine the age of rock formations.
Learn more about elements on the periodic table.