Hydrogen (H)

Hydrogen, denoted by the symbol “H” and having the atomic number 1, is the most elementary and widespread element in the cosmos. It accounts for about 75% of the elemental mass of the universe, playing a vital role not just in astronomical phenomena but also in a variety of scientific, industrial, and environmental applications on Earth. This article explores the characteristics, uses, and importance of hydrogen, illuminating its central role in numerous sectors.

Elemental Characteristics

  • Symbol: H
  • Atomic Number: 1
  • Atomic Weight: 1.008
  • Element Classification: Non-metal
  • Discovered By: Henry Cavendish
  • Discovery Date: 1766
  • Name Origin: From the Greek words “hydro” (water) and “genes” (creator)
  • Density: 0.08988 g/L at 0°C and 1 atm
  • Melting Point: -259.16°C (-434.49°F; 14.01 K)
  • Boiling Point: -252.879°C (-423.182°F; 20.271 K)
  • Appearance: Colorless gas
  • Atomic Radius: 53 pm
  • Atomic Volume: 14.1 cm³/mol
  • Covalent Radius: 31 pm
  • Ionic Radius: Not applicable for its most stable form
  • Specific Heat: 14.304 J/(g·K) at 25°C (gas)
  • Fusion Heat: 0.117 kJ/mol
  • Evaporation Heat: 0.904 kJ/mol
  • Thermal Conductivity: 0.1805 W/(m·K)
  • Debye Temperature: Not well defined for gases
  • Pauling Negativity Number: 2.20
  • First Ionizing Energy: 1312.0 kJ/mol
  • Oxidation States: -1, +1 (commonly +1)
  • Electronic Configuration: 1s¹
  • Lattice Structure: Hexagonal (when solidified under extreme conditions)
  • Lattice Constant: Not applicable in standard conditions
  • Lattice C/A Ratio: Not applicable in standard conditions

Hydrogen’s notable simplicity, consisting of only one proton and one electron, renders it the lightest element. At Earth’s surface conditions, hydrogen naturally occurs as a diatomic gas (H₂), meaning its molecules comprise two hydrogen atoms. This gas is colorless, odorless, tasteless, and highly flammable, and it is significantly less dense than air.

Cosmic Abundance

In the cosmic expanse, hydrogen predominantly exists in a plasma state, especially within stars like the Sun. The fusion of hydrogen atoms in the intense pressure and heat of stellar cores is the primary process that powers stars, fostering the creation of helium while releasing immense energy as light and heat.

Hydrogen on Earth

Free hydrogen gas is relatively scarce on Earth due to its lightweight nature, which enables it to escape the planet’s gravitational field with ease. The majority of Earth’s hydrogen is bound with other elements in compounds such as water (H₂O), hydrocarbons (the main constituents of fossil fuels), and organic compounds.

Industrial and Environmental Uses

Hydrogen’s industrial applications are diverse. It is essential for producing ammonia (NH₃) via the Haber process, a crucial component in fertilizers that sustain global agriculture. It’s also used in refining petroleum, creating methanol, and synthesizing hydrochloric acid, besides acting as a reducing agent in various metallurgical operations.

Recently, hydrogen has emerged as a focal point in renewable energy and sustainability discussions. It’s considered a promising clean fuel, especially when produced through water electrolysis powered by renewable energy sources. Hydrogen fuel cells, which transform hydrogen’s chemical energy into electricity, offer a potential eco-friendly alternative for powering vehicles, emitting only water vapor.

Challenges and Future Prospects

The broad adoption of hydrogen as a clean energy source is hampered by several challenges, including the efficient, cost-effective production, storage, and transport of hydrogen, along with the need for infrastructure to support hydrogen fuel cells.

Hydrogen’s elemental simplicity, ubiquity, and adaptability keep it at the forefront of scientific research and industrial application. Its cosmic role, earthly uses, and renewable energy potential underscore its significance across varied disciplines. As technological advancements continue and our comprehension of hydrogen expands, its capability to aid in achieving sustainable energy solutions becomes ever more promising, positioning it as a fundamental element in the pursuit of a cleaner, more sustainable future.


Helium (He)