Sodium
Atomic Data
| Atomic Number | 11 |
| Symbol | Na |
| Atomic Weight | 22.99 u |
| Density (STP) | 0.971 g/cm³ |
| Melting Point | 97.72 °C (370.87 K) |
| Boiling Point | 882.85 °C (1156 K) |
| Electronegativity | 0.93 (Pauling) |
| Electron Config. | 1s² 2s² 2p&sup6; 3s¹ |
| Oxidation States | +1 |
| Phase at STP | Solid |
| Category | Alkali metal |
| Period / Group | 3 / 1 |
| CAS Number | 7440-23-5 |
Electron Configuration
1s2 2s2 2p6 3s1
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| 2p | 6 | 10 | ||
| M | 3 | 3s | 1 | 11 |
| Total | 11 | 11 | ||
Isotopes of Sodium
Sodium is a monoisotopic element with only one naturally occurring stable isotope, 23Na, which accounts for 100% of all natural sodium. All other sodium isotopes are artificially produced and radioactive, with half-lives ranging from milliseconds to about 2.6 years for 22Na.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Sodium-23 | ²³Na | 11 | 12 | 100% | Stable |
Abundance & Occurrence
Sodium is the sixth most abundant element in Earth's crust at approximately 23,600 parts per million by mass, found chiefly in silicate minerals such as albite (NaAlSi₃O₈), halite (NaCl), and soda ash (Na₂CO₃) deposits. Metallic sodium never occurs free in nature due to its extreme reactivity with moisture and air. Seawater is the world's most accessible sodium reservoir, with a mean sodium concentration of about 10,800 ppm, making sodium by far the dominant dissolved metal in the ocean.
EARTH'S CRUST COMPOSITION (BY MASS)
SEAWATER DISSOLVED IONS (BY MASS %)
Discovery & History
Safety & Handling
- Violent water reactivity: Metallic sodium reacts aggressively with water and moisture, releasing flammable hydrogen gas and highly caustic sodium hydroxide. Even small pieces can ignite; larger quantities explode on water contact. Never allow metallic sodium near water sources.
- Skin and eye burns: Direct skin contact with sodium metal or its hydroxide solution causes severe alkali burns. Always use neoprene or heavy-duty rubber gloves, a face shield, and a lab coat when handling metallic sodium.
- Fire hazard: Sodium burns with a persistent yellow-orange flame. Class D extinguishers (dry sand or sodium chloride powder) must be used exclusively — never water, CO₂, or foam, which react with sodium and worsen the fire.
- Storage requirements: Store sodium metal under inert mineral oil or in sealed containers filled with dry inert gas (argon or nitrogen). Keep away from halogenated solvents, which can react explosively with sodium.
- Sodium compound hazards: Sodium hydroxide (lye) is severely corrosive; sodium hypochlorite (bleach) releases toxic chlorine gas when acidified; sodium cyanide is acutely lethal. Handle all concentrated sodium compounds with appropriate personal protective equipment and in a ventilated fume hood.
- Dietary considerations: While sodium is essential for human health, excessive intake is linked to hypertension and cardiovascular disease. The WHO recommends less than 2 g of sodium (equivalent to 5 g of table salt) per day for adults.
Sodium in the Real World
Real-World Uses
- Table salt production — Sodium chloride (NaCl) is produced in vast quantities for food seasoning, food preservation, water softening, and de-icing roads. It is the primary commercial form of sodium and one of the most widely used chemicals globally, with world production exceeding 300 million tonnes per year.
- Sodium-vapor street lamps — Low-pressure sodium lamps produce the distinctive yellow-orange glow common in street lighting, emitting nearly monochromatic light at 589 nm for high energy efficiency and excellent visibility in fog and rain.
- Coolant in fast nuclear reactors — Liquid metallic sodium serves as a primary coolant in sodium-cooled fast reactors (SFRs) because of its excellent thermal conductivity, low neutron moderation, and high boiling point of 883°C at atmospheric pressure.
- Soap manufacturing — Sodium hydroxide (NaOH, caustic soda) reacts with fats and oils through saponification to produce solid bar soaps. Most commercial bar soaps are sodium salts of fatty acids derived from this process.
- Paper and pulp processing — The kraft (sulfate) pulping process uses sodium hydroxide and sodium sulfide to dissolve lignin in wood chips, producing the majority of the world's paper pulp and kraft paper products.
- Chemical synthesis — Metallic sodium is used as a powerful reducing agent in the synthesis of pharmaceuticals, dyes, and organic compounds. It is also used in the production of titanium metal and tetraethyllead (historically).
- Baking and food processing — Sodium bicarbonate (baking soda, NaHCO₃) is a leavening agent essential to baking. Sodium glutamate (MSG) enhances savoury flavour, and sodium nitrite is used as a preservative and colour fixative in cured meats.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
Why does sodium react so violently with water?
Sodium reacts vigorously with water because it has a single loosely held valence electron that it readily donates to water molecules, producing sodium hydroxide and hydrogen gas. The reaction is highly exothermic — the heat generated can ignite the hydrogen gas, causing the characteristic flame and popping. Larger pieces of sodium can explode on contact with water.
What are the most common sodium compounds?
The most common sodium compounds are sodium chloride (NaCl, table salt), sodium hydroxide (NaOH, caustic soda), sodium bicarbonate (NaHCO₃, baking soda), sodium carbonate (Na₂CO₃, washing soda), and sodium hypochlorite (NaOCl, bleach). Sodium chloride is by far the most widely encountered, present in seawater and essential to the human diet.
Who discovered sodium and when?
Sodium was first isolated as a pure element by Humphry Davy in 1807 using electrolysis of molten sodium hydroxide at the Royal Institution in London. Davy performed this experiment just days after isolating potassium by the same method. The element had been known in compound form since antiquity through common salt.
What role does sodium play in the human body?
Sodium is an essential electrolyte that regulates fluid balance, blood pressure, and nerve signal transmission in the human body. It works alongside potassium to maintain the electrochemical gradient across cell membranes via the sodium-potassium pump (Na⁺/K⁺-ATPase). The average adult body contains about 100 g of sodium, mostly in blood plasma and extracellular fluids.
What is the difference between sodium and salt?
Sodium (Na) is a pure chemical element — a soft, reactive metal. Salt (sodium chloride, NaCl) is a compound made of sodium and chlorine ions in a 1:1 ratio. Table salt is roughly 39% sodium by mass, so 1 gram of salt contains about 390 mg of sodium. While elemental sodium is dangerous, the sodium in salt is safely ionised and essential for human health in moderate amounts.