Hydrogen (H)
Hydrogen (symbol H) is the chemical element with atomic number 1: a nonmetal, a gas at 0 °C, with an atomic mass of 1.008 u. Discovered in 1766 (Henry Cavendish).
Hydrogen is the simplest atom there is: one proton and one electron. Born a few minutes after the Big Bang, it still makes up roughly three quarters of the mass of ordinary matter in the Universe. Stars, the Sun included, shine by fusing hydrogen into helium. On Earth it is found mostly bound to oxygen in water, and industry now sees it as an energy carrier.
Key facts
- Atomic number
- 1
- Symbol
- H
- French name
- Hydrogène
- Atomic mass
- 1.008 u
- Molar mass
- 1.008 g/mol
- Family
- Nonmetals
- Position
- period 1, group 1, s-block
- State at 0 °C
- Gas
- Melting point
- -259.2 °C
- Boiling point
- -252.9 °C
- Density
- 0.00009 g/cm³
- Electronegativity (Pauling)
- 2.2
- First ionization energy
- 1,312 kJ/mol
- Atomic radius
- 25 pm
- Electron configuration
- 1s¹
- Abundance in Earth's crust
- 1,400 ppm (10th most abundant element)
- Indicative price
- 1 $/kg (order of magnitude)
- Radioactive
- no
- Discovery
- 1766, Henry Cavendish
Origin of the name
From the Greek hydro (water) and genes (forming): “water-former.”
What does hydrogen look like?
A colorless, odorless, tasteless gas, fourteen times lighter than air. Liquefied at −253 °C, it becomes a clear, extremely low-density liquid.
Where is hydrogen found?
About 74% of the mass of ordinary matter in the Universe and more than 90% of its atoms. On Earth it is almost entirely combined: in ocean water, hydrocarbons and living things. It accounts for about 10% of the human body's mass, but nearly 6 atoms out of 10.
Natural sources
- Water (H₂O)
- Natural gas (methane, CH₄)
- Oil and hydrocarbons
How is hydrogen produced?
About 95 million tonnes a year, more than 95% of it made from natural gas or coal (steam methane reforming), which emits a lot of CO₂. Electrolysis, which splits water using electricity, is still only a small fraction. Deposits of natural (“white”) hydrogen are being explored, notably in Lorraine, France.
Top producers
- China
- United States
- India
- Russia
What is hydrogen used for?
- Making ammonia for fertilizers (Haber-Bosch process).
- Oil refining (removing sulfur from fuels).
- Methanol production and hydrogenation of edible oils.
- Rocket fuel (liquid hydrogen).
- Fuel cells for vehicles and energy storage.
In everyday life
- The water you drink (2 hydrogen atoms per molecule)
- The fertilizers that grew the wheat in your bread
- Margarine (hydrogenated oils)
- Sunlight, produced by the Sun's fusion
Role in living things
Essential to all life: it is in water, sugars, fats, proteins and DNA. Hydrogen bonds hold the two strands of the DNA double helix together and give water its remarkable properties.
Hazards of hydrogen
Extremely flammable: mixed with air at anywhere from 4% to 75%, it can explode, with a flame that is almost invisible in daylight. It is not toxic, but in a confined space it can suffocate by displacing oxygen. It also embrittles some steels by seeping into the metal.
Cosmic origin
- Big Bang: Forged in the first three minutes of the Universe, 13.8 billion years ago.
History of hydrogen
Paracelsus and Robert Boyle had already noticed a flammable gas when dissolving metals in acids. In 1766, Henry Cavendish identified it as a distinct substance, which he called “inflammable air.” In 1783, Lavoisier showed that burning it produces water and named it hydrogen, “water-former.”
Did you know?
- Almost all the hydrogen in your body was formed in the Big Bang, about 13.8 billion years ago.
- Deep inside Jupiter, the pressure is so great that hydrogen turns into a conducting liquid metal, which drives the planet's giant magnetic field.
- The first crewed hydrogen balloon flight took place in Paris as early as 1783, with Jacques Charles aboard.
- The Sun turns about 600 million tonnes of hydrogen into helium every second.
Isotopes of hydrogen
Two stable isotopes: ordinary hydrogen, with no neutron at all, and deuterium, twice as heavy. Together with radioactive tritium, they are the only isotopes with names of their own.
- hydrogen-1: 99.989% of natural hydrogen, stable. Its nucleus, a lone proton, is what MRI scanners actually image.
- hydrogen-2: 0.012% of natural hydrogen, stable. Deuterium makes heavy water, the moderator in some nuclear reactors, and is a fusion fuel.
- hydrogen-3: radioactive, half-life 12.3 years. Tritium lights up watch dials and exit signs without batteries, and will fuel fusion reactors such as ITER.
Common compounds
Water (H₂O) · Glucose (C₆H₁₂O₆) · Table sugar (C₁₂H₂₂O₁₁) · Alcohol (C₂H₅OH) · Caffeine (C₈H₁₀N₄O₂) · Urea (CO(NH₂)₂) · Citric acid (C₆H₈O₇) · Vitamin C (C₆H₈O₆) · Aspirin (C₉H₈O₄) · Paracetamol (C₈H₉NO₂) · Chlorophyll a (C₅₅H₇₂MgN₄O₅) · Hydroxyapatite (Ca₅(PO₄)₃(OH)) · Baking soda (NaHCO₃) · Vinegar (CH₃COOH) · Ammonia (NH₃) · Caustic soda (NaOH) · Hydrogen peroxide (H₂O₂) · Gypsum (plaster) (CaSO₄·2H₂O) · Butane (C₄H₁₀) · Propane (C₃H₈) · Methane (CH₄) · Malachite (Cu₂CO₃(OH)₂) · Sulfuric acid (H₂SO₄) · Ammonium nitrate (NH₄NO₃)
Related elements
Same family (nonmetals): Carbon (C), Nitrogen (N), Oxygen (O), Phosphorus (P), Sulfur (S), Selenium (Se).
Same column (group 1): Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs), Francium (Fr).