Hydrogen Facts - H or Atomic Number 1

Quick Facts about the Element Hydrogen

Over 75% of the matter in the universe is hydrogen. Helium accounts for most of the other quarter, with the other elements accounting for less than one percent.
Over 75% of the matter in the universe is hydrogen. Helium accounts for most of the other quarter, with the other elements accounting for less than one percent. Reinhold Wittich/Stocktrek Images, Getty Images

Hydrogen is the chemical element with the element symbol H and atomic number 1. It's essential for all life and abundant in the universe, so it's one element you should get to know better. Here are basic facts about the first element in the periodic table, hydrogen.

Fast Facts: Hydrogen

  • Element Name: Hydrogen
  • Element Symbol: H
  • Atomic Number: 1
  • Group: Group 1
  • Classification: Nonmetal
  • Block: s-block
  • Electron Configuration: 1s1
  • Phase at STP: Gas
  • Melting Point: 13.99 K ​(−259.16 °C, ​−434.49 °F)
  • Boiling Point: 20.271 K ​(−252.879 °C, ​−423.182 °F)
  • Density at STP: 0.08988 g/L
  • Oxidation States: -1, +1
  • Electronegativity (Pauling Scale): 2.20
  • Crystal Structure: Hexagonal
  • Magnetic Ordering: Diamagnetic
  • Discovery: Henry Cavendish (1766)
  • Named By: Antoine Lavoisier (1783)

Atomic Number: 1

Hydrogen is the first element in the periodic table, meaning it has an atomic number of 1 or 1 proton in each hydrogen atom. The name of the element comes from the Greek words hydro for "water" and genes for "forming," since hydrogen bonds with oxygen to form water (H2O). Robert Boyle produced hydrogen gas in 1671 during an experiment with iron and acid, but hydrogen wasn't recognized as an element until 1766 by Henry Cavendish.

Atomic Weight: 1.00794

This makes hydrogen the lightest element. It is so light, the pure element isn't bound by Earth's gravity. So, there is very little hydrogen gas left in the atmosphere. Massive planets, such as Jupiter, consist mainly of hydrogen, much like the Sun and stars. Even though hydrogen, as a pure element, bonds to itself to form H2, it's still lighter than a single atom of helium because most hydrogen atoms don't have any neutrons. In fact, two hydrogen atoms (1.008 atomic mass units per atom) are less than half the mass of one helium atom (atomic mass 4.003).

Hydrogen Facts

  • Hydrogen is the most abundant element. About 90% of the atoms and 75% of the element mass of the universe is hydrogen, usually in the atomic state or as plasma. Although hydrogen is the most abundant element in the human body in terms of numbers of atoms of the element, it's only 3rd in abundance by mass, after oxygen and carbon, because hydrogen is so light. Hydrogen exists as a pure element on Earth as a diatomic gas, H2, but it's rare in Earth's atmosphere because it is light enough to escape gravity and bleed into space. The element remains common at the Earth's surface, where it is bound into water and hydrocarbons to be the third most abundant element.
  • There are three natural isotopes of hydrogen: protium, deuterium, and tritium. The most common isotope of hydrogen is protium, which has 1 proton, 0 neutrons, and 1 electron. This makes hydrogen the only element that can have atoms without any neutrons! Deuterium has 1 proton, 1 neutron, and 1 electron. Although this isotope is heavier than protium, deuterium is not radioactive. However, tritium does emit radiation. Tritium is the isotope with 1 proton, 2 neutrons, and 1 electron.
  • Hydrogen gas is extremely flammable. It is used as a fuel by the space shuttle main engine and was associated with the famous explosion of the Hindenburg airship. While many people consider oxygen to be flammable, it actually doesn't burn. However, it's an oxidizer, which is why hydrogen is so explosive in air or with oxygen.
  • Hydrogen compounds commonly are called hydrides.
  • Hydrogen may be produced by reacting metals with acids (e.g., zinc with hydrochloric acid).
  • The physical form of hydrogen at room temperature and pressure is a colorless and odorless gas. The gas and liquid are nonmetals, but when hydrogen is compressed into a solid, the element is an alkali metal. Solid crystalline metallic hydrogen has the lowest density of any crystalline solid.
  • Hydrogen has many uses, though most hydrogen is used for processing fossil fuels and in the production of ammonia. It is gaining importance as an alternate fuel that produces energy by combustion, similar to what happens in fossil fuel engines. Hydrogen is also used in fuel cells that react hydrogen and oxygen to produce water and electricity.
  • In compounds, hydrogen can take a negative charge (H-) or a positive charge (H+).
  • Hydrogen is the only atom for which the Schrödinger equation has an exact solution.


  • Emsley, John (2001). Nature's Building Blocks. Oxford: Oxford University Press. pp. 183–191. ISBN 978-0-19-850341-5.
  • "Hydrogen". Van Nostrand's Encyclopedia of Chemistry. Wylie-Interscience. 2005. pp. 797–799. ISBN 978-0-471-61525-5.
  • Stwertka, Albert (1996). A Guide to the Elements. Oxford University Press. pp. 16–21. ISBN 978-0-19-508083-4.
  • Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. ISBN 978-0-8493-0464-4.
  • Wiberg, Egon; Wiberg, Nils; Holleman, Arnold Frederick (2001). Inorganic chemistry. Academic Press. p. 240. ISBN 978-0123526519.
mla apa chicago
Your Citation
Helmenstine, Anne Marie, Ph.D. "Hydrogen Facts - H or Atomic Number 1." ThoughtCo, Apr. 5, 2023, thoughtco.com/hydrogen-element-facts-606474. Helmenstine, Anne Marie, Ph.D. (2023, April 5). Hydrogen Facts - H or Atomic Number 1. Retrieved from https://www.thoughtco.com/hydrogen-element-facts-606474 Helmenstine, Anne Marie, Ph.D. "Hydrogen Facts - H or Atomic Number 1." ThoughtCo. https://www.thoughtco.com/hydrogen-element-facts-606474 (accessed May 29, 2023).