The chemical element hydrogen is classified as a non-metal, though it can become metallic under extremely high pressure. It was discovered in 1766 by Henry Cavendish.
Discovery of Hydrogen
A classic experiment in chemistry classes involves adding a metal, like magnesium, to an acid. The metal reacts, forming a salt and releasing hydrogen from the acid. This hydrogen gas bubbles up from the liquid, and students collect small amounts for further experiments, such as the “pop test.”
The first recorded instance of human-produced hydrogen dates back to the 16th century, in a process similar to those used in schools today. The Swiss physician Paracelsus dissolved iron in sulfuric acid and observed gas being released. He described the experiment as “the air arises and bursts forth like wind.” However, he didn’t identify the properties of hydrogen.
Later, in 1670, Robert Boyle, an English scientist, added iron to sulfuric acid and found that the resulting gas (hydrogen) only burned if there was air present, and a part of the air (now known as oxygen) was consumed during the combustion process.
In 1766, Henry Cavendish, an English scientist, officially recognized hydrogen as a distinct element by reacting hydrochloric acid with zinc. He called it “flammable air of metals” and noted it was the same gas, regardless of the metal or acid used. Cavendish also discovered that hydrogen produced water when burned.
The French chemist Antoine Lavoisier named the element hydrogen in 1783. The name comes from the Greek words ‘hydro,’ meaning water, and ‘genes,’ meaning creator, as hydrogen is one of the elements that make up water.
By 1806, the English chemist Humphry Davy ran a strong electrical current through purified water, discovering that it separated into hydrogen and oxygen, providing insight into the true nature of chemical bonds.
Appearance and Characteristics
- Harmful Effects: Hydrogen is highly flammable, and its flame is almost invisible, posing risks of accidental burns.
- Characteristics:
- Hydrogen is the simplest and lightest element.
- It is the most abundant in the universe, making up over 90% of all atoms.
- In its most common form, the hydrogen atom consists of one proton, one electron, and no neutrons. It is the only element that can exist without neutrons.
- Hydrogen exists as a colorless, odorless gas under standard conditions, forming diatomic molecules (H₂).
- It burns and forms explosive mixtures with air.
- On Earth, hydrogen is mainly found in water (H₂O), and very little free hydrogen exists in the atmosphere due to its lightness, allowing it to escape into space.
Uses of Hydrogen
- Large quantities of hydrogen are used in the Haber-Bosch process (for producing ammonia), hydrogenation of fats and oils, methanol production, hydrocracking, and hydrodesulfurization.
- Liquid hydrogen is used as rocket fuel, such as in the Space Shuttle.
- The heavier isotopes of hydrogen (deuterium and tritium) are used in nuclear fusion.
- The hydrogen economy has been proposed as a replacement for the current hydrocarbon economy (oil, gas, and coal). Energy is produced when hydrogen burns with oxygen, with the only byproduct being water.
Abundance and Isotopes of Hydrogen
- Crustal abundance: 1400 ppm by weight (0.14%), 2.9% by moles.
- Solar abundance: 75% by weight, 93% by moles.
- Production cost, pure: $12 per 100g.
- Bulk production cost: $1 per 100g.
Hydrogen is commercially produced by reacting superheated steam with methane or carbon. In laboratories, it can be produced by the action of acids on metals like zinc or magnesium, or through electrolysis of water.
Isotopes: Hydrogen has three isotopes, 1H (protium), 2H (deuterium), and 3H (tritium). Deuterium and tritium are used in nuclear fusion. Protium is the most abundant isotope, while tritium is unstable with a half-life of about 12 years and 4 months.
Chemical Properties
| Property | Value |
|---|---|
| Symbol | H |
| Atomic number | 1 |
| Valence | +1 |
| Atomic weight | 1.00797 |
| Boiling point (°C) | -252.7 |
| Melting point (°C) | -259.7 |
| Density (Kg/m³) | 0.0899 |
| Atomic structure | 1s¹ |
Related Biology Terms
- Evolution: The process of change in populations of organisms over time, adapting them to their environment.
- Inorganic: Molecules that contain little carbon and are not produced by living organisms.
- Organic: Molecules synthesized in living organisms that contain many carbon-carbon bonds.
- Ribosome: One of the earliest cellular machines, capable of producing proteins from RNA and amino acids.