Quick Facts
| Property | Value |
|---|---|
| Symbol | K |
| Atomic Number | 19 |
| Atomic Mass | 39.098 u |
| Category | Alkali Metal |
| Period | 4 |
| Group | 1 |
| Block | s |
| Electron Configuration | [Ar] 4s¹ |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Solid |
| Density | 0.862 g/cm³ |
| Melting Point | 63.5°C (336.7 K) |
| Boiling Point | 759°C (1032 K) |
| Appearance | Soft, silvery-white metal |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Ar] 4s¹ |
| Electronegativity | 0.82 (Pauling scale) |
| First Ionization Energy | 418.8 kJ/mol |
| Atomic Radius | 227 pm |
| Covalent Radius | 203 pm |
| Van der Waals Radius | 275 pm |
History and Discovery
Discovered by: Humphry Davy Year of Discovery: 1807 Location: London, England
Etymology
The English name "potassium" comes from "potash" (pot ash), the residue left in pots after burning wood. The symbol "K" comes from the Latin "kalium," derived from Arabic "al-qali" meaning "calcined ashes."
Discovery Story
Humphry Davy isolated potassium in 1807 by electrolyzing molten potassium hydroxide (caustic potash). It was the first metal isolated by electrolysis. Davy initially called it "potassium" but some scientists preferred "kalium" from Latin, which is why we use the symbol K.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ³⁹K | 93.26% | Stable | - |
| ⁴⁰K | 0.012% | 1.25 billion years | β⁻, β⁺, EC |
| ⁴¹K | 6.73% | Stable | - |
Occurrence
Natural Abundance
Potassium is the seventh most abundant element in Earth's crust (about 2.1%). It is never found free due to its high reactivity. Major sources include sylvite (KCl), carnallite, and potash deposits. Significant deposits exist in Canada, Russia, Belarus, and Germany.
Extraction and Production
- Electrolysis: Of molten potassium chloride (modern method)
- Chemical Reduction: Historically using sodium reduction
- Sources: Potash mining, brine extraction
- Global potash production: about 70 million tons annually
Applications and Uses
Agricultural Applications
- Potash fertilizers (essential plant nutrient)
- Potassium chloride (KCl) - most common fertilizer form
- Potassium sulfate for chloride-sensitive crops
Industrial Applications
- Glass manufacturing
- Soap and detergent production
- Potassium hydroxide (caustic potash)
- Heat transfer (liquid metal in some nuclear reactors)
Chemical Applications
- Potassium carbonate (potash)
- Potassium permanganate (oxidizer, water treatment)
- Potassium nitrate (fertilizer, gunpowder)
Other Uses
- Photography (potassium bromide)
- Food processing (potassium sorbate preservative)
- Specialty alloys
Biological Role
Potassium is essential for life. It is the main intracellular cation and is critical for nerve transmission, muscle contraction, and cellular function.
In the Human Body
- About 0.2% of body mass (140 g in adult)
- Main intracellular cation
- Essential for nerve impulse transmission
- Regulates heartbeat and muscle contraction
- Daily requirement: 2,600-3,400 mg
Dietary Sources
Bananas, potatoes, spinach, beans, tomatoes, and dairy products are rich in potassium.
Safety and Hazards
Toxicity
Potassium ion is essential but excess (hyperkalemia) can cause cardiac arrhythmias. Potassium metal and its compounds can be hazardous.
Handling Precautions
- Reacts violently with water (more so than sodium)
- Can ignite spontaneously in moist air
- Store under mineral oil or inert gas
- Produces hydrogen when reacting with water (fire/explosion risk)
- Causes severe burns
Environmental Impact
Potassium is naturally abundant and essential for ecosystems. Fertilizer runoff can contribute to eutrophication.
Interesting Facts
- Potassium is the second least dense metal after lithium
- Potassium-40 is naturally radioactive and contributes to background radiation in the body
- The sodium-potassium pump in cells uses about 20-25% of the body's resting energy
- Potassium compounds produce a violet flame color
- Bananas are slightly radioactive due to their potassium-40 content