Quick Facts
| Property | Value |
|---|---|
| Symbol | Na |
| Atomic Number | 11 |
| Atomic Mass | 22.990 u |
| Category | Alkali Metal |
| Period | 3 |
| Group | 1 |
| Block | s |
| Electron Configuration | [Ne] 3s¹ |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Solid |
| Density | 0.968 g/cm³ |
| Melting Point | 97.79°C (370.94 K) |
| Boiling Point | 882.94°C (1156.09 K) |
| Appearance | Soft, silvery-white metal |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Ne] 3s¹ |
| Electronegativity | 0.93 (Pauling scale) |
| First Ionization Energy | 495.8 kJ/mol |
| Atomic Radius | 186 pm |
| Covalent Radius | 166 pm |
| Van der Waals Radius | 227 pm |
History and Discovery
Discovered by: Humphry Davy Year of Discovery: 1807 Location: London, England
Etymology
The symbol "Na" comes from the Latin "natrium," derived from the Greek "nitron" (sodium carbonate). The English name "sodium" comes from the Medieval Latin "sodanum," a headache remedy containing sodium.
Discovery Story
Humphry Davy isolated sodium in 1807 by electrolysis of molten sodium hydroxide (caustic soda) using his newly invented voltaic pile. This was just days after he had isolated potassium using the same method. Sodium compounds, especially salt (NaCl), had been known and used since ancient times.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ²³Na | 100% | Stable | - |
| ²²Na | Synthetic | 2.6 years | β⁺ |
| ²⁴Na | Synthetic | 15 hours | β⁻ |
Occurrence
Natural Abundance
Sodium is the sixth most abundant element in Earth's crust (about 2.3%). It is never found free in nature due to its reactivity. Major sources include halite (rock salt, NaCl), trona, and various sodium-containing minerals. Seawater contains about 1.1% sodium chloride.
Extraction and Production
- Downs Process: Electrolysis of molten sodium chloride
- Castner Process: Historical method using sodium hydroxide
- Sources: Primarily rock salt and seawater
- Global production of metallic sodium: about 100,000 tons annually
Applications and Uses
Industrial Applications
- Sodium vapor lamps (street lighting)
- Heat transfer medium in nuclear reactors
- Descaling metals
- Production of other chemicals
Chemical Applications
- Reducing agent in metallurgy (titanium production)
- Synthesis of organic compounds
- Production of sodium peroxide
- Pharmaceutical manufacturing
Sodium Compounds
- Sodium chloride (table salt, food preservation)
- Sodium hydroxide (caustic soda, soaps, paper)
- Sodium carbonate (glass, detergents)
- Sodium bicarbonate (baking soda)
Other Uses
- Automotive airbags (sodium azide)
- Antifreeze mixtures
- Street lighting
Biological Role
Sodium is essential for life. It is a major electrolyte that helps regulate fluid balance, nerve transmission, and muscle function.
In the Human Body
- About 0.14% of body mass
- Main extracellular cation
- Essential for nerve impulse transmission
- Regulates blood pressure and fluid balance
- Daily requirement: about 500 mg (often exceeded)
Dietary Sources
Table salt, processed foods, bread, cheese, and cured meats are major sodium sources. Most people consume far more than the recommended 2,300 mg/day.
Safety and Hazards
Toxicity
Elemental sodium is corrosive and dangerous. Excess dietary sodium is linked to hypertension and cardiovascular disease.
Handling Precautions
- Reacts violently with water (producing hydrogen and heat)
- Can spontaneously ignite in air when finely divided
- Store under mineral oil or inert atmosphere
- Causes severe burns on contact with skin
- Use class D fire extinguisher for sodium fires
Environmental Impact
Sodium compounds are generally benign. However, road salt runoff can affect freshwater ecosystems and contaminate groundwater.
Interesting Facts
- Sodium is so soft it can be cut with a knife
- It floats on water while reacting violently with it
- Sodium-potassium pumps in cell membranes consume about 20-25% of the body's resting energy
- Sodium vapor lamps produce the characteristic yellow-orange glow of street lights
- The human body contains about 100 grams of sodium