hydrogen
What Is Hydrogen?
Hydrogen is the simplest chemical element and the first element on the periodic table. A hydrogen atom contains one proton and one electron, and hydrogen is the most abundant element in the universe.
The Simplest Atom
The most common isotope of hydrogen, called protium, has a nucleus containing one proton and no neutron, with one electron surrounding the nucleus.
Hydrogen is the lightest chemical element. Its simple atomic structure and ability to form bonds with many other elements make it fundamental to chemistry, water, organic compounds, stars, fuels, and living matter.
Under ordinary conditions, elemental hydrogen commonly exists as molecular hydrogen (H2)—two hydrogen atoms bonded together. H2HUBB covers molecular hydrogen separately in the next H2 Basics lesson.
Hydrogen Is Everywhere—But Not Always in the Same Form
Hydrogen is widespread throughout the universe and in everyday matter. The form and chemical bonding of hydrogen determine whether it is atomic hydrogen, molecular hydrogen, or part of another compound.
Stars & the Universe
Hydrogen is the most abundant element in the universe and a major component of stars and interstellar matter.
Water
Every water molecule contains two hydrogen atoms chemically bonded to one oxygen atom, producing H2O.
Organic Compounds
Hydrogen is present throughout organic chemistry and living systems as part of molecules containing carbon and other elements.
Watch: What Is Hydrogen?
Prefer a visual explanation? This H2Minutes episode introduces hydrogen and the foundational chemistry covered on this page.