Quick Facts
| Property | Value |
|---|---|
| Symbol | H |
| Atomic Number | 1 |
| Atomic Mass | 1.008 u |
| Category | Nonmetal |
| Period | 1 |
| Group | 1 |
| Block | s |
| Electron Configuration | 1s¹ |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Gas |
| Density | 0.00008988 g/cm³ |
| Melting Point | -259.16°C (14.01 K) |
| Boiling Point | -252.87°C (20.28 K) |
| Appearance | Colorless, odorless gas |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | 1s¹ |
| Electronegativity | 2.20 (Pauling scale) |
| First Ionization Energy | 1312.0 kJ/mol |
| Atomic Radius | 53 pm |
| Covalent Radius | 31 pm |
| Van der Waals Radius | 120 pm |
History and Discovery
Discovered by: Henry Cavendish Year of Discovery: 1766 Location: London, England
Etymology
The name "hydrogen" comes from the Greek words "hydro" (water) and "genes" (forming), meaning "water-former." Antoine Lavoisier named it in 1783 after observing that burning hydrogen produces water.
Discovery Story
Henry Cavendish first recognized hydrogen as a distinct substance in 1766, calling it "inflammable air." He discovered that it produced water when burned, a crucial observation. Earlier, Robert Boyle had produced hydrogen in 1671 by reacting iron filings with dilute acids, but did not recognize it as a unique element. Lavoisier later gave hydrogen its modern name and proved it was an element.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ¹H (Protium) | 99.98% | Stable | - |
| ²H (Deuterium) | 0.02% | Stable | - |
| ³H (Tritium) | Trace | 12.32 years | β⁻ |
Occurrence
Natural Abundance
Hydrogen is the most abundant element in the universe, comprising about 75% of all normal matter by mass. On Earth, it is the third most abundant element on the surface, primarily found in water (H₂O) and organic compounds. Free hydrogen gas is rare in Earth's atmosphere (less than 1 ppm) because it escapes into space.
Extraction and Production
- Steam Reforming: Most commercial hydrogen is produced by reacting natural gas with steam at high temperatures
- Electrolysis: Splitting water using electricity produces high-purity hydrogen
- Coal Gasification: Reacting coal with oxygen and steam
- Biological Production: Certain algae and bacteria can produce hydrogen
Applications and Uses
Industrial Applications
- Ammonia synthesis (Haber-Bosch process) for fertilizers
- Petroleum refining (hydrocracking and hydrodesulfurization)
- Methanol production
- Hydrogenation of fats and oils
Energy Applications
- Hydrogen fuel cells for vehicles and power generation
- Rocket propellant (liquid hydrogen with liquid oxygen)
- Energy storage medium for renewable energy
Technological Applications
- Semiconductor manufacturing
- Welding and cutting metals (hydrogen torch)
- Cooling agent for electrical generators
Other Uses
- Weather balloons
- Reducing agent in metallurgy
- Hydrogen peroxide production
Biological Role
Hydrogen is essential for life. It is a component of water and all organic molecules including carbohydrates, proteins, lipids, and nucleic acids.
In the Human Body
- Approximately 10% of human body mass is hydrogen
- Essential component of water (60-70% of body weight)
- Found in all organic molecules in the body
- Critical for pH balance and cellular functions
Dietary Sources
Hydrogen is obtained through water and all food sources, as it is present in virtually all organic compounds.
Safety and Hazards
Toxicity
Hydrogen gas is non-toxic but can act as a simple asphyxiant by displacing oxygen in enclosed spaces.
Handling Precautions
- Highly flammable gas - ignites easily in air (4-75% concentration range)
- Forms explosive mixtures with air and oxygen
- Store and handle away from heat, sparks, and open flames
- Use proper ventilation
- Invisible flame when burning
Environmental Impact
Hydrogen is environmentally benign. When burned, it produces only water vapor with no carbon emissions, making it an attractive clean energy carrier.
Interesting Facts
- Hydrogen is the lightest and simplest element, with just one proton and one electron
- The Sun converts about 600 million tons of hydrogen into helium every second through nuclear fusion
- Liquid hydrogen is used as rocket fuel because of its high energy-to-weight ratio
- Hydrogen was used in early airships (like the Hindenburg) before being replaced by helium due to flammability
- A cubic meter of water contains about 111 kg of hydrogen