|Name, Symbol, Number||potassium, K, 19 |
|Series ||alkali metals|
|Group, Period, Block||1(IA), 4, s|
|Density, Hardness ||856 kg/m3, 0.4|
|Appearance ||silvery white|
|Atomic weight ||39.0983 amu|
|Atomic radius (calc.) ||220 (243) pm|
|Covalent radius ||196 pm|
|van der Waals radius ||275 pm|
|Electron configuration ||[Ar]4s1|
|e- 's per energy level||2, 8, 8, 1|
|Oxidation states (Oxide) ||1 (strong base)|
|Crystal structure ||cubic body centered|
|State of matter ||solid|
|Melting point ||336.53 K (146.08 °F)|
|Boiling point ||1032 K (1398 °F)|
|Molar volume ||45.94 ×10-6 m3/mol|
|Heat of vaporization ||79.87 kJ/mol|
|Heat of fusion ||2.334 kJ/mol|
|Vapor pressure ||1.06×10-4Pa at __ K|
|Speed of sound ||2000 m/s at 293.15 K|
|Electronegativity ||0.82 (Pauling scale) |
|Specific heat capacity ||757 J/(kg*K)|
|Electrical conductivity ||13.9 106/(m·ohm)|
|Thermal conductivity ||102.4 W/(m*K)|
|1st ionization potential ||418.8 kJ/mol|
|2nd ionization potential ||3052 kJ/mol|
|3rd ionization potential ||4420 kJ/mol|
|4th ionization potential ||5877 kJ/mol|
|5th ionization potential ||7975 kJ/mol|
|6th ionization potential ||9590 kJ/mol|
|7th ionization potential ||11343 kJ/mol|
|8th ionization potential ||14944 kJ/mol|
|9th ionization potential ||16963.7 kJ/mol|
|10th ionization potential ||48610 kJ/mol|
|Most stable isotopes|
|SI units & STP are used except where noted.
Potassium is a chemical element in the periodic table that has the symbol K (L. kalium) and atomic number 19. The name potassium comes from potash the source it was first isolated from. This is a soft, silvery-white metallic alkali metal that occurs naturally bound to other elements in seawater and many minerals. It oxidizes rapidly in air, is very reactive, especially in water, and resembles sodium chemically.
With a density less than that of water, potassium is the second lightest metal after lithium. It is a soft solid that can easily be cut with a knife and is silvery in color on fresh surfaces. It oxidizes in air rapidly and must be stored in mineral oil or kerosene for preservation.
Similar to other alkali metals, potassium reacts violently with water producing hydrogen. When in water, it may catch fire spontaneously. Its salts emit a violet color when exposed to a flame.
Many potassium salts are very important, and include, potassium; bromide, carbonate, chlorate, chloride, chromate , cyanide, dichromate, hydroxide, iodide, nitrate, sulfate.
Potassium was discovered in 1807 by Sir Humphry Davy, who derived it from caustic potash (KOH). This alkali metal was the first metal that was isolated by electrolysis.
This element makes up about 2.4% of the weight of the Earth's crust and is the seventh most abundant element in it. Due to its insolubility , it is very difficult to obtain potassium from its minerals.
However, other minerals, such as carnallite , langbeinite , polyhalite , and sylvite are found in ancient lake and sea beds. These minerals form extensive deposits in these environments, making extracting potassium and its salts more economical. The principle source of potassium, potash is mined in California, Germany, New Mexico, Utah, and in other places around the world. At 3000 ft below the surface of Saskatchewan are large deposits of potash which may become important sources of this element and its salts in the future.
The oceans are another source of potassium but the quantity present in a given volume of seawater is relatively low compared to sodium.
Potassium can be isolated through electrolysis of its hydroxide in a process that has changed little since Davy. Thermal methods also are employed in potassium production, using potassium chloride. Potassium is almost never found unbound in nature. However, in living organisms K+ ions are important in the physiology of excitable cells.
There are seventeen isotopes of potassium known to exist. The non-synthetic form of potassium are composed of three isotopes: K-39 (93.3%), K-40 (0.01%) and K-41 (6.7%). Naturally occurring K-40 decays to stable Ar-40 (11.2%) by electron capture and by positron emission, and decays to stable Ca-40 (88.8%) by negatron emission; K-40 has a half-life of 1.250 × 109 years.
The decay of K-40 to Ar-40 is commonly used as a method for dating rocks. The conventional K-Ar dating method depends on the assumption that the rocks contained no argon at the time of formation and that all the subsequent radiogenic argon (i.e., Ar-40) was quantitatively retained, i.e., closed system. Minerals are dated by measurement of the concentration of potassium, and the amount of radiogenic Ar-40 that has accumulated. The minerals that are best suited for dating include biotite, muscovite, and plutonic/high grade metamorphic hornblende, and volcanic feldspar; whole rock samples from volcanic flows and shallow instrusives can also be dated if they are unaltered.
Outside of dating, potassium isotopes have been used extensively as tracers in studies of weathering. They have also be used for nutrient cycling studies because potassium is a macro-nutrient required for life.
K-40 occurs in natural potassium (and thus in some commercial salt substitutes) in sufficient quantity that large bags of those substitutes can be used as a radioactive source for classroom demonstrations.
Solid potassium reacts violently with water. This metal should therefore be kept under a mineral oil such as kerosene and handled with care.
Potassium in Diet
Potassium is a nessesary mineral in daily nutrition; it assists in muscle contraction and in maintaining fluid and electrolyte balance in body cells. Potassium is also important in sending nerve impulses as well as releasing energy from protein, fat, and carbohydrates during metabolism. A shortage of potassium can cause a potentially fatal condition known as hypokalemia. Eating a variety of foods that contain potassium is the best way to get an adequate amount. Healthy individuals who eat a balanced diet rarely need supplements. Many fruits, vegetables, and meats contain potassium.