Hydrogen is a chemical element. Its atomic number is 1, which makes it the simplest, known element in the entire universe. Hydrogen is the true primordial substance, the first atom produced after the big bang. All chemical elements were formed from hydrogen by the processes of nuclear fusion.
Hydrogen glows purple when it is in the plasma state.
In its pure form on Earth, hydrogen is usually a gas. Hydrogen is also one of the parts that make up a water molecule. Hydrogen is important because it is the fuel that powers the Sun and other stars. Hydrogen makes up about 75% of the entire universe. Hydrogen's symbol on the Periodic Table of Elements is H.
Pure hydrogen is normally made of two hydrogen atoms connected together. Scientists call these diatomic molecules. Hydrogen will have a chemical reaction when mixed with most other elements. It has no color or smell.

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