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Oxidation & Electrons | Appearance & Characteristics Reactions | Compounds | Radius | Conductivity Abundance & Isotopes 
Nasa image of salt deposits, including potash at Great Salt Lake, Utah |
General:
| Name: Potassium | Symbol: K |
| Type: Alkali Metal | Atomic weight: 39.0983 |
| Density @ 293 K: 0.862 g/cm3 | Atomic volume: 45.46 cm3/mol |
| Discovered: Sir Humphry Davy discovered potassium in 1807 by the electrolysis of potassium hydroxide (potash). The metal collected at the cathode. This was the first metal isolated by electrolysis. The name potassium is from the English word 'potash', originally meaning an alkali extracted with water in a pot of ash of burnt wood or tree leaves. | |
States
| State (s, l, g): solid | |
| Melting point: 336.5 K (63.4 oC) | Boiling point: 1038.7 K (765.6 oC) |
Energies
| Specific heat capacity: 0.75 J g-1 K-1 | Heat of atomization: 89 kJ mol-1 |
| Heat of fusion: 2.334 kJ mol-1 | Heat of vaporization (sublimation): 79.870 kJ mol-1 |
| 1st ionization energy: 418.8 kJ mol-1 | 2nd ionization energy: 3051.3 kJ mol-1 |
| 3rd ionization energy: 4411.3 kJ mol-1 | Electron affinity: 48.385 kJ mol-1 |
Oxidation & Electrons
| Shells: 2,8,8,1 | Electron configuration: [Ar] 4s1 |
| Minimum oxidation number: 0 | Maximum oxidation number: 1 |
| Min. common oxidation no.: 0 | Max. common oxidation no.: 1 |
| Electronegativity (Pauling Scale): 0.82 | Polarizability volume: 43.4 Å3 |
Appearance & Characteristics
| Structure: bcc: body-centered cubic | Color: silvery-white |
| Harmful Effects: Potassium is considered to be non-toxic. Due to its highly reactive nature, elemental potassium must be handled with extreme care. | Hardness: 0.4 mohs |
| Characteristics: Potassium is a soft, silvery-white, low melting metal that can easily be cut with a knife. It rapidly tarnishes in air forming a dull oxide coating. Potassium is one of the most reactive and electropositive of all metals. It reacts violently with water producing hydrogen gas and potassium hydroxide. Potassium burns with a lilac colored flame. | |
| Uses: Potassium is an essential constituent for plant growth and the greatest demand for potassium compounds is for fertilizers. Potassium chloride is used as a healthier alternative for table salt. Potassium hydroxide is a strong alkali and an important industrial chemical. Glass treated with liquid potassium is much stronger than standard glass. Potassium nitrate is used in gunpowder. | |
Reactions
| Reaction with air: vigorous, ⇒ KO2 | Reaction with 6 M HCl: vigorous, ⇒ H2, KCl |
| Reaction with 3 M HNO3: vigorous, ⇒ H2, NOx, KNO3 | Reaction with 6 M NaOH: vigorous, ⇒ H2, KOH |
Compounds
| Oxide(s): K2O | Chloride(s): KCl |
| Hydride(s): KH |
Radius
| Atomic radius: 220 pm | Ionic radius (1+ ion): 152 pm |
| Ionic radius (2+ ion): pm | Ionic radius (3+ ion): pm |
| Ionic radius (2- ion): pm | Ionic radius (1- ion): pm |
Conductivity
| Thermal conductivity: 102.5 W m-1 K-1 | Electrical conductivity: 0.164 x 106 S cm-1 |
Abundance & Isotopes
| Abundance earth's crust: 1.5 % by weight, 0.8 % by moles | |
| Abundance solar system: 4 ppm by weight, 100 parts per billion by moles | |
| Cost, pure: 100 $/100g | |
| Cost, bulk: 65 $/100g | |
| Source:Potassium is never found free in nature; it is too reactive. It in fact forms compounds from which it is difficult to separate. Potassium is obtained commercially by electrolysis of the hydroxide, much in the same manner as prepared by Sir Humphry Davy's first process. Thermal methods are also used to obtain potassium from potassium chloride. | |
| Isotopes: Potassium has 20 isotopes whose half-lives are known, with mass numbers 35 to 54. Of these, two are stable, 39K, and 41K. Over 93.2% of of naturally occurring potassium is in the form of 39K. | |
