What is Hydrogen?
Diagram of a hydrogen atom
June 2016 - Hydrogen is the simplest kind of
atom, and in the very earliest days after the
Big Bang hydrogen was the only kind of atom in the new Universe. A hydrogen atom, like other atoms, has a
nucleus. The nucleus of a hydrogen atom is made of just one
proton. Around the nucleus, there is just one
electron, which goes around and around the nucleus.
Eagle Nebula
The first hydrogen atoms in
space gradually grouped together into clumps called
nebulae. When a nebula got dense enough, it formed a
star. Inside these stars, there was a lot of heat and
gravity. The strong
gravity pressed the hydrogen atoms together, and four hydrogen atoms squashed together to form a new atom, with two
protons, two
neutrons, and two
electrons. This is a
helium atom.
The neutrons had just a little less energy than the protons, and the extra energy shot off into space and became
heat and
light for us. Inside most of the
stars
in the Universe, billions of hydrogen atoms are changing into helium
atoms every day. When a star runs out of hydrogen, it becomes a
supergiant or a
red giant star.
The first men riding in a hydrogen balloon
(in
France, 1783 AD)
Not all the hydrogen stayed inside stars, though. Some of it began
spinning around the outside of the star, orbiting the new star. This
hydrogen mixed with other kinds of atoms, and gradually gravity pulled
them together into
planets. There are many hydrogen atoms on Earth (though most of them are combined with other atoms to make
molecules).
Because hydrogen atoms are so simple, they are very
light. They are lighter than
air, so if you fill a balloon with hydrogen, it will float up to the sky (like a
helium
balloon that you can get at the store). But the most important things
about hydrogen for us are that two hydrogen atoms combine with one
oxygen atom to make a
molecule of
water, and that hydrogen atoms combine with
carbon atoms to make
hydrocarbons, which all living things are made of.
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