Atomic Number: 1
Atomic Weight: 1.00794
Melting Point: 13.81 K (-259.34°C or -434.81°F)
Boiling Point: 20.28 K (-252.87°C or -423.17°F)
Density: 0.0899 grams per liter at 273 K and 1atm
Phase at Room Temperature: Gas
Element Classification: Non-metal
Period Number: 1
Group Number: 1
Group Name: none

A single hydrogen atom is composed of one negatively-charged electron in association with a positively-charged proton; there are no neutrons in the nucleus of the atom. Hydrogen is found in diatomic form – meaning two “atoms” combine to form a single molecule.

Hydrogen is a colorless, odorless, tasteless, and nontoxic gas at atmospheric temperatures and pressures. A stable molecule because of its high bond strength, hydrogen becomes reactive at elevated temperatures or with the aid of catalysts. When cooled to its boiling point of -423°F (-253°C), hydrogen becomes a liquid that is approximately 93% lighter than water. All other gases - except helium - become solids at this temperature.

Hydrogen is flammable and burns in air at concentrations as low as 4% with a pale blue, almost invisible flame. In its gaseous form, hydrogen dissipates quickly making it difficult for hydrogen to reach concentrations necessary for combustion.

Hydrogen is the only element that has different names for its isotopes. There are only three naturally occurring isotopes of hydrogen:

• Protium, ¹H, is the most common isotope which has a nucleus consisting of single proton.
• Deuterium, ²H or D, an isotope of hydrogen, is used in nuclear fission applications as a moderator to slow down neutrons, and is also used in nuclear fusion reactions. Deuterium compounds have applications in chemistry and biology in studies of reaction isotope effects.
• Tritium, ³H or T, produced in nuclear reactors, is used to construct hydrogen bombs. It is also used as an isotopic label in the biosciences as a tracer and as a radiation source in luminous paints.