Hydrogen notes

Hydrogen is a chemical element with atomic numer 1 and the symbol H

It is the lightest atom on the periodic table
It is a colorless gas at standart temperatures and pressures
It's melting point is −259.16 °C and it's boiling point is −252.879 °C
The ground state energy level of the electron in a hydrogen atom is −13.6 eV.
The most common isotope of hydrogen, termed protium
symbol 1H, has one proton and no neutrons.
And hydrogen has three naturally occurring isotopes, denoted 1
H, 2H and 3H

Hydrogen gas is a highly flammable gas
Hydrogen gas forms explosive mixtures with air in concentrations from 4 to 74 percent
And the explosive reactions may for example be triggered by a spark or heat.

Hydrogen is commonly used in power stations as a coolant in generators.
Because of its low density, low viscosity, and the highest specific heat and thermal conductivity of all gases.

And the Suns energy comes from nuclear fusion of hydrogen

Hydrogens phases
- Gaseous hydrogen
   At standard temperatures and pressures
- Liquid hydrogen
   Hydrogen was liquefied for the first time by using regenerative cooling
- Slush hydrogen
   Slush hydrogen is a combination of liquid hydrogen and
   solid hydrogen at the triple point with a lower temperature
   and a higher density than liquid hydrogen
- Solid hydrogen 
   Solid is achieved by decreasing the temperature below hydrogens
   melting point of −259.14 °C
- Metallic hydrogen
   At high pressure and temperatures, metallic hydrogen might exist in a liquid form rather than a solid form