Potassium was first found in the ashes of burned plants. It was discovered by Sir Humphry Davy when he experimented with potash (a mixture of plant ashes with water). The name potassium comes from potash, but the chemical symbol, K, is taken from kalium (Latin for "ash"). This element is never found pure in nature, but is present in minerals such as aphthalite and sylvite. It is vital to the human body, as it helps muscles and nerves function properly.
To this end, the diet should be composed of foods rich in potassium, such as bananas, tubers and avocados, which contain potassium chloride.
In small amounts, this element can enhance flavors such as carbonated water. It is also a healthy alternative to sodium chloride, or common salt, and an important ingredient in saline drops to rehydrate critically ill patients. Potassium nitrate, KNO3, is used in gunpowder and in hardened glass screens for cell phones.
Summary of properties (K)
| Atomic weight | 39.0983(1) |
| Discoverer (year) | Davy, Humphry (1807) |
| Natural form | metallic solid (body centered cubic) |
| Electron configuration | [Ar] 4s1 |
| Melting point (ºC) | 64 |
| Boiling point (ºC) | 774 |
| Abundance in earth's crust (ppm) | 20900 |
| Isotope (abundance) | 39K (93.2581), 40K (0.0117), 41K (6.7302) |
| Density g/cm3 | 1.78 |
| Van der Waals radius (pm) | 275 |
| Covalent radius (pm) | 200 |
| Electronegativity (Pauling) | 0.82 |
| Vaporization enthalpy (kJ/mol) | 77.50 |
| Enthalpy of fusion (kJ/mol) | 2.33 |
| Specific heat capacity (J/g·K) at 25ºC and 1 atm | 0.76 |
| Thermal conductivity (W/cm·K) at 25ºC and 1 atm | 1.030 |
| Oxidation state | +1 |
| Electron affinity (eV) | 0.50 |
| 1st Ionization potential (eV) | 4.3407 |
