Congrats to tupelo916 for the FTF!
First: The junior high chemistry lesson:
Hydrogen (Latin: hydrogenium, from Greek: hydro: water, genes: forming) is a chemical element in the periodic table that has the symbol H and atomic number 1. At standard temperature and pressure it is a colorless, odorless, non-metallic, univalent, highly flammable diatomic gas. Hydrogen is the lightest and most abundant element in the universe. It is present in water and in all organic compounds and living organisms. Hydrogen is able to react chemically with most other elements. Stars in their main sequence are overwhelmingly composed of hydrogen in its plasma state. This element is used in ammonia production, as a lifting gas, as an alternative fuel, and more recently as a power source of fuel cells.
Hydrogen is the lightest chemical element with its most common isotope consisting of just a single proton and electron. At standard temperature and pressure conditions, hydrogen forms a diatomic gas, H2, with a boiling point of only 20.27 K and a melting point of 14.02 K. Under exceedingly high pressures, like those found at the center of gas giants, the molecules lose their identity and the hydrogen becomes a liquid metal (see metallic hydrogen). Under the exceedingly low pressure conditions found in space, hydrogen tends to exist as individual atoms, simply because there is no way for them to combine; clouds of H2 form and are associated with star formation.
This element plays a vital role in powering the Universe through the proton-proton reaction and carbon-nitrogen cycle. (These are nuclear fusion processes that release huge amounts of energy through combining hydrogen atoms into helium.)
Hydrogen (French for water-maker, from Greek hudôr, "water" and gennen, "generate") was first recognized as a distinct substance in 1766 by Henry Cavendish. Cavendish stumbled upon it when experimenting with acids and mercury. Although he wrongly assumed that hydrogen was a compound of mercury (and not of the acid), he was still able to describe many of hydrogen's properties quite accurately. Antoine Lavoisier gave the element its name and proved that water was made of hydrogen and oxygen. One of its first uses was for balloons. The hydrogen was obtained by mixing sulfuric acid and iron. Deuterium, an isotope of hydrogen, was discovered by Harold C. Urey by distilling a sample of water multiple times. Urey received a Nobel prize for his discovery in 1934. In the same year, the third isotope, tritium, was discovered.
Hydrogen is the most abundant element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms. This element is found in great abundance in stars and gas giant planets. It is very rare in the Earth's atmosphere (1 ppm by volume). The most common source for this element on Earth is water, which is composed two parts hydrogen to one part oxygen (H2O).
