Hydrogen Facts 1

Hydrogen Facts - Element
Hydrogen is the first element on the periodic table, with atomic number 1 and element symbol H.

Hydrogen (H) is the first element of the periodic table and the most abundant element in the universe. Here is a collection of hydrogen facts, including its properties, uses, and sources.

Glowing Hydrogen Gas
Vial of ionized hydrogen gas. Hydrogen glows violet when ionized. Creative Commons License

Basic Hydrogen Facts

Name: Hydrogen

Atomic Number: 1

Element Symbol: H

Group: 1

Period: 1

Block: s

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.

Common Isotopes:

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 is 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.

Hydrogen Atom
Electron configuration of a hydrogen atom.

Physical Data

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 Data

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

Fun Hydrogen Facts

Here are some interesting and fun facts about hydrogen:

Nursery of New Stars
Hubble Space Telescope composite image of NGC 604 nebula. This “nursery of new stars” is a vast region of ionized hydrogen gas forming new stars. Credit: NASA
  • Hydrogen is the lightest of the elements.
  • Hydrogen is the most abundant of the elements. It accounts for approximately 75% of the element mass of the universe.
  • Hydrogen is a colorless and odorless gas at room temperature and pressure.
  • Hydrogen gas at room temperature and pressure is 14 times lighter than air. It is so light, it easily escapes Earth’s gravity and enters space.
  • Hydrogen gas is extremely flammable when mixed with oxygen. Burning hydrogen gas caused the famous Hindenburg airship disaster.
  • Burning hydrogen gas in air produces water.
  • One method of preparing hydrogen gas is 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.


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  • Scerri, Eric (2007). The Periodic System, Its Story and Its Significance. New York: Oxford University Press. ISBN 978-0-19-530573-9.
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