# hydrogen

Pronunciation: say "HY-druh-juhn" /ˈhaɪdɹəd͡ʒən/

## Noun

1. The chemical element with atomic number 1 and symbol H, the lightest of all elements, with an atomic weight of 1.008.
   - Simple: The lightest of all chemical elements, written with the symbol H.
   - _Hydrogen sits at the top of the periodic table as element number one._
   - _Most of the visible matter in the universe is hydrogen._
2. The element in its molecular form (H₂), a flammable gas that has no color or smell at room temperature.
   - Simple: A colorless gas with no smell that catches fire very easily.
   - _Hydrogen ignites readily when mixed with air and exposed to a spark._
   - _Engineers store hydrogen under high pressure to fuel the cells._
3. A quantity or sample of the element or its molecular gas, as handled in practice.
   - Simple: A measured amount of the gas that can be used, stored, or tested.
   - _The technician drew off a small amount of hydrogen for analysis._
   - _Each cylinder holds enough hydrogen for a full week of testing._
4. A single atom of hydrogen, the lightest chemical element, made of one proton and one electron.
   - Simple: A single atom of the lightest element, with one proton and one electron.
   - _In methane, four hydrogen atoms bond to a single carbon atom._
   - _A single hydrogen loses its electron to become a bare proton._
5. A single molecule of the molecular species H₂, formed from two hydrogen atoms bonded together.
   - Simple: A single molecule of the gas, made of two atoms joined together.
   - _When light strikes it, each hydrogen can break apart into two reactive atoms._
   - _Two atoms share a bond to form a single hydrogen._
6. The isotope hydrogen-1 (protium), having one proton and no neutrons, as distinct from deuterium and tritium.
   - Simple: A form of the lightest element that has one proton and no neutrons.
   - _Most hydrogen on Earth is protium, with deuterium making up only a tiny fraction._
   - _Unlike deuterium, ordinary hydrogen carries no neutron in its nucleus._

## Origin

From French hydrogène, coined by Louis-Bernard Guyton de Morveau and Antoine Lavoisier, from Ancient Greek húdōr ("water") plus gennáō ("I bring forth"), corresponding to hydro- plus -gen.

Source: DictionaryAI, https://dictionaryai.com/define/hydrogen (written from Wiktionary data, CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/).