Potassium

Potassium is a chemical      Potassium - Calcium
element in the periodic
table that has the      Na
symbol K and atomic     K
number 19. This is a    RbÊÊ [Image:K-TableImage.png]
soft, silvery-white     Ê           Full table
metallic alkali metal   Ê

that occurs naturally                         General
bound to other elements
in seawater and many    Name, Symbol, Number       Potassium, K, 19
minerals. It oxidizes   Series                     Alkali metals
rapidly in air, is very Group, Period, Block       1(IA), 4 , s
reactive, especially in
water, and resembles    Density, Hardness          856 kg/m3, 0.4
sodium chemically.      Appearance                 silvery white
                                Atomic Properties
                        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

Notable Characteristics Oxidation states (Oxide)   1 (strong base)
Potassium is the second Crystal structure          cubic body centered
lightest and the most                   Physical Properties
reactive and most       State of matter            solid
electropositive of the
metals. This is a soft  Melting point              336.53 K (146.08 ¡F)
solid that easily is    Boiling point              1032 K (1398 ¡F)
cut with a knife and is
silvery in color on     Molar volume               45.94 ×10-3 m3/mol
fresh surfaces. It      Heat of vaporization       79.87 kJ/mol
oxidizes in air rapidly Heat of fusion             2.334 kJ/mol
and must be stored in
mineral oil for         Vapor pressure             1.06×10-4Pa at __ K
preservation.           Speed of sound             2000 m/s at 293.15 K
Similar to other alkali                    Miscellaneous
metals potassium        Electronegativity          0.82 (Pauling scale)
decomposes in water
with the release of     Specific heat capacity     757 J/(kg*K)
hydrogen. When in water Electrical conductivity    13.9 106/m ohm
it catches fire
spontaneously and its   Thermal conductivity       102.4 W/(m*K)
salts emit a violet     1st ionization potential   418.8 kJ/mol
color when exposed to a
flame.                  2nd ionization potential   3052 kJ/mol

                        3rd ionization potential   4420 kJ/mol
Applications
                        4th ionization potential   4420 kJ/mol

   * Potassium oxide,   5th ionization potential   7975 kJ/mol
     best known as
     potash, is         6th ionization potential   9590 kJ/mol
     primarily used in
     fertilizer.        7th ionization potential   11343 kJ/mol

   * Potassium chloride 8th ionization potential   14944 kJ/mol
     is used as a
     substitute for     9th ionization potential   16963.7 kJ/mol
     table salt and is
     also used to stop  10th ionization potential  48610 kJ/mol

     the heart in                       Most Stable Isotopes
     executions by
     lethal injection.   iso    NA     half-life       DM     DE MeV   DP
     It is also used in 39K  93.26%   K is stable with 20 neutrons
     fertilizer.
   * Potassium nitrate                                               40Ca
                        40K  0.012%   1.277 E9y    beta-     1.311
     is used in                                    epsilon   1.505   40Ar
     gunpowder.
   * Potassium          41K  6.73%    K is stable with 22 neutrons
     carbonate is used
     in glass               SI units & STP are used except where noted.
     manufacture
   * This element is an essential component needed in plant growth and is
     found in most soil types.
   * In animal cells potassium is vital to keeping cells alive (see Na-K
     pump)
   * NaK an alloy of sodium and potassium is used as a heat-transfer medium.

Many potassium salts are very important, and include, potassium; bromide,
carbonate, chlorate, chloride, chromate, cyanide, dichromate, hydroxide,
iodide, nitrate, sulfate.

History

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.

Occurrence

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 is never found unbound in nature and is produced through
electrolysis of its hydroxide in a process that has changed little since
Davy. Thermal methods also are employed in potassium production

Isotopes

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.

Precautions

Potassium reacts violently with water. This metal should therefore be kept
under a mineral oil such as kerosene for this reason.

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