What Is Hydrogen?
Hydrogen is the simplest element. Each atom of hydrogen has only one
proton. It is also the most plentiful gas in the universe. Stars like
the sun are made primarily of hydrogen.
The sun is basically a giant ball of hydrogen and helium gases. In
the sun's core, hydrogen atoms combine to form helium atoms. This
process — called fusion — gives off radiant energy.
This radiant energy sustains life on Earth. It
gives us light and makes plants grow. It makes the wind blow and rain
fall. It is stored as chemical energy in fossil fuels. Most of the
energy we use today originally came from the sun's radiant energy.
Hydrogen gas is so much lighter than air that it rises fast and is
quickly ejected from the atmosphere. This is why hydrogen as a gas (H2) is not found by itself on Earth. It is found only in compound form with other elements. Hydrogen combined with oxygen, is water (H2O). Hydrogen combined with carbon forms different compounds, including methane (CH4),
coal, and petroleum. Hydrogen is also found in all growing things — for
example, biomass. It is also an abundant element in the Earth's crust.
Hydrogen has the highest energy content of any common fuel by weight
(about three times more than gasoline), but the lowest energy content
by volume (about four times less than gasoline).