Potassium is a bright silver element that is a very light metal, with only lithium being lighter, and is the seventh most abundant element in the earth's crust. It is strongly ionic, has 24 known isotopes, and combines rapidly with oxygen when exposed to the air. Pure potassium also has a exothermic reaction on contact with water, separating out hydrogen gas and igniting it due to the heat generated in the process. The element potassium has violent reactions with several compounds as does its close relative sodium. When it comes into contact with halogens, bromine, and sulfuric acid, it can explode, so it must be handled with extreme care.
One of the important chemical properties of potassium is that it acts as an electrolyte in the human body to conduct electricity. This makes it important in such biological functions as heart and muscle contractions. In fact, potassium chloride is used to stop the heart during heart surgery. In high quantities, it has also been used since 1982 as a form of lethal injection for prisoners condemned to death in the United States, with China following the practice in 1997, and other nations later on.
The right amount of potassium in the body is affected by levels of sodium and magnesium, and, if these levels are higher, more potassium is sometimes necessary to balance them. Since potassium concentration can be very important, medical conditions defining low levels, called hypokalemia, and high levels, called hyperkalemia, have been established in medicine. Most people get enough potassium for health in their diets, as it is found in all red meat and a wide variety of fruits and vegetables.
As of 2006, over 95% of the potassium produced worldwide was used as agricultural fertilizer, and the bulk of this was in the form of potassium chloride. Properties of potassium make it an important nutrient in plants in other ionized forms as well, such as potassium sulfate and potassium nitrate. Potassium nitrate is also used as a key ingredient in gunpowder and to strengthen glass. Together, Canada and Russia produce about half the world's potassium supply each year, and Canada is estimated to have 59.8% of world reserves of the metal, with Russia having 13.6%.
One of the unique physical properties of potassium is its ability to act as a super oxide. KO2 has been used on Russian Vostok, Soyuz, and other spacecraft as an oxygen-generating compound because of this. The properties of potassium hydroxide make it a strong base material used in many laboratory experiments to neutralize various acids. The diverse properties of potassium in combination with other elements make it a versatile chemical for everything from the manufacturing of inks to gold mining and the baking of bread.