Basic Hydrogen Facts
Atomic Number: 1
Element Symbol: H
Element Family: Nonmetal
Atomic Mass: [1.00784; 1.00811] IUPAC guidelines
1.008 is commonly used for a single value
Electron Configuration: 1s1
Discovery: Henry Cavendish in 1766.
Cavendish was the first to recognize hydrogen as an element. Others had prepared samples of hydrogen gas without identifying it as an element. Cavendish called his discovery ‘inflammable air’. Antoine Lavoisier suggested the name ‘hydrogene’ in 1783 and hydrogen was adopted soon after.
Name Origin: Hydro (Greek for “water”) Gene (Greek for “forming”). Lavoisier showed if you combusted hydrogen with oxygen, water was formed.
Protium is the most common isotope. It has 1 proton and 1 electron. 99.98% of all naturally occurring hydrogen is protium.
Deuterium is 1 proton, 1 neutron and 1 electron. This isotope is commonly denoted by the letter D. The name comes from the Greek word “deuteros” meaning “second”. Approximately 0.02% of naturally occurring hydrogen is deuterium.
Tritium contains 1 proton, 2 neutrons and 1 electron. This isotope si commonly denoted by the letter T. The name comes from the Greek word “tritos” meaning “third”. Trition is radioactive and decays by β decay into He-3 with a half-life of 12.32 ± 0.02 years. 10-18% of naturally occurring hydrogen is tritium.
Density: 0.000082 g/cm3
Melting Point: 13.99 K (-259.16 ºC or -434.182 ºF)
Boiling Point: 20.271 K (-252.879 ºC or -423.182 ºF)
Triple Point: 13.8033 K at 7.041 kPa
Critical Point: 32.938 K at 1.2858 MPa
State at 20ºC: Gas
Heat of Fusion: 0.117 kJ/mol for H2.
Heat of Vaporization: 0.904 kJ/mol for H2.
Molar Heat Capacity: 28.836 J/mol·K for H2.
Atomic Radius: 1.10 Å
Covalent Radius: 0.32 Å
Van der Waals Radius: 1.2 Å
Electron Affinity: 72.769 kJ/mol
Electronegativity: (Pauling scale): 2.20
1st Ionization Energy: 1312.05 kJ/mol
Common Oxidation States: 1, -1
- Hydrogen is the lightest of the elements.
- Hydrogen is the most abundant of the elements accounting for approximately 75% of the element mass of the universe.
- Hydrogen gas at room temperature and pressure is colorless and odorless.
- Hydrogen gas at room temperature and pressure is 14 times lighter than air. It is so light, it can escape Earth’s gravity and enter space.
- Hydrogen gas is extremely flammable when mixed with oxygen. Burning hydrogen gas was responsible for the famous Hindenburg airship disaster.
- Burning hydrogen gas produces water.
- Hydrogen gas can be produced by reacting metal with acid.
- Positive ions of hydrogen are called hydrons. Negative hydrogen ions are hydrides.
- Hydrogen is largely used in industry to produce ammonia and process fossil fuels.
- Hydrogen is often prepared by electrolysis of water. It is also prepared by running steam across heated carbon or the reaction of acids on metals.
Learn more about elements on the periodic table.