hydrogen

/ˈhaɪdrədʒən/

/ˈhaɪdrədʒɪn/

Other forms: hydrogens

Hydrogen is the very lightest chemical element, and the first one listed on the periodic table. Some scientists believe that hydrogen will one day be used as fuel in cars and trucks.

Hydrogen's atomic number is one, because it has a single proton in its nucleus. It's a light, flammable gas that's the most common element in the universe. Humans use hydrogen in many ways, including to make ammonia, fertilizers, and petroleum products. It's also used in rocket fuel, and some see its potential as a clean alternative to oil and gas. Hydrogen's Greek roots mean "water-producing," from the fact that when it's exposed to oxygen, hydrogen produces water.

Definitions of hydrogen

1. noun

   a nonmetallic univalent element that is normally a colorless and odorless highly flammable diatomic gas; the simplest and lightest and most abundant element in the universe
   synonyms: H, atomic number 1

   types:

   tritium

   a radioactive isotope of hydrogen; atoms of tritium have three times the mass of ordinary hydrogen atoms

   type of:

   chemical element, element

   any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter

   gas

   a fluid in the gaseous state having neither independent shape nor volume and being able to expand indefinitely