|Name, Symbol, Number||Potassium, K, 19|
|Group, Period, Block||1(IA), 4 , s|
|Density, Hardness||856 kg/m3, 0.4|
|Atomic weight||39.0983 amu|
|Atomic radius (calc.)||220 (243) pm|
|Covalent radius||196 pm|
|van der Waals radius||275 pm|
|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 ×1010-3 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||4420 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.|
|Table of contents|
7 External Links
Potassium is the second lightest and the most reactive and most electropositive of the metals. This is a soft solid that easily is cut with a knife and is silvery in color on fresh surfaces. It oxidizes in air rapidly and must be stored in mineral oil for preservation.
Similar to other alkali metals potassium decomposes in water with the release of hydrogen. When in water it catches fire spontaneously and 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 (English, potash L. kalium) was discovered in 1807 by Sir Humphry Davy who derived it from caustic potash (KOH. This alkali metal and 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 envrionments making extracting potassium and its salts more economical. The principle source of pottassium, potash is mined in California, Germany, New Mexico, Utah, and in other places around the world. At 3000 ft below the surface of Saskatchewan lies 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 quantify 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. 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, K isotopes have been used extensively in studies of weathering; K isotopes have also be used for nutrient cycling studies because K is a macro-nutrient required for life.
Potassium reacts violently with water. This metal should therefore be kept under a mineral oil such as kerosene for this reason.