Potassium
Potassium is a chemical element, in the periodic table that has the symbol K and atom number 19.
- Symbol: K
- Group: Alkali metal
- Crystal Structure: Cubicbody centered
- Atomic number: 19
- Atomic weight: 39.0983
- Shells: 2,8,8,1
- Filling orbital: 4s1
- Melting point: 63.65°C
- Boiling point: 774°C
- Electronegativity: 0.82
- Covalent radius: 2.03 Å
- Atomic radius: 2.77 Å
- Atomic volume: 45.46 cm3/mol
- First ionization potential: 4.341 V
- 2nd ionization potential: 31.625 V
- 3rd ionization potential: 45.72 V
- Oxidation states: 1
- Density at 293 K: 0.862 g/cm3
- Specific heat: 0.75 J/gK
- Heat of vaporization: 79.870 kJ/mol
- Heat of fusion: 2.334 kJ/mol
- Electrical conductivity: 0.139 106:/cm ohm
- Thermal conductivity: 1.024 W/cmK
Isotopes
Potassium has three naturally occurring isotopes: 39K (93.3%), 40K (0.01%) and 41K (6.7%). Naturally occurring 40K decays to stable 40Ar (11.2%) by electron capture and by positron emission, and decays to stable 40Ca (88.8%) by negatron emission; 40K has a half-life of 1.250 x 109 years. The decay of 40K to 40Ar 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., 40Ar) was quantitatively retained, i.e., closed system. Minerals are dated by measurement of the concentration of potassium, and the amount of radiogenic 40Ar 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.
External Link:
Los Alamos National Laboratory - Potassium
See: Periodic table