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Hydrogen is a chemical element; it has symbol H and atomic number 1. It is the lightest element and, at standard conditions, is a gas of diatomic molecules with the formula H 2, sometimes called dihydrogen, [11] hydrogen gas, molecular hydrogen, or simply hydrogen. It is colorless, odorless, [12] non-toxic, and highly combustible.
Depiction of a hydrogen atom showing the diameter as about twice the Bohr model radius. (Image not to scale) A hydrogen atom is an atom of the chemical element hydrogen.The electrically neutral hydrogen atom contains a single positively charged proton in the nucleus, and a single negatively charged electron bound to the nucleus by the Coulomb force.
H 2, the chemical formula for hydrogen gas (dihydrogen) Deuterium (Hydrogen-2, H-2, 2 H), the isotope of hydrogen with one proton, one neutron, and one electron Other uses in science and mathematics
Liquid hydrogen (H 2 (l)) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H 2 form. [4] To exist as a liquid, H 2 must be cooled below its critical point of 33 K. However, for it to be in a fully liquid state at atmospheric pressure, H 2 needs to be cooled to 20.28 K (−252.87 °C; −423.17 °F). [5]
Hydrogen (1 H) has three naturally occurring isotopes: 1 H, 2 H, and 3 H. 1 H and 2 H are stable, while 3 H has a half-life of 12.32(2) years. [3] [nb 1] Heavier isotopes also exist; all are synthetic and have a half-life of less than 1 zeptosecond (10 −21 s). [4] [5] Of these, 5 H is the least stable, while 7 H is the most.
Emissions from burning hydrogen can be negligible but emissions from producing hydrogen are currently higher than direct combustion of the source. [37] Hydrogen has a wide flammability range (3–70% H 2 in air) in comparison with other fuels. [35] As a result, it can be combusted in an internal combustion engine over a wide range of fuel-air ...
Water molecules have two hydrogen atoms and one oxygen atom. While H 2 is not very reactive under standard conditions, it does form compounds with most elements. Hydrogen can form compounds with elements that are more electronegative, such as halogens (F, Cl, Br, I), or oxygen; in these compounds hydrogen takes on a partial positive charge. [1]
The four visible hydrogen emission spectrum lines in the Balmer series. H-alpha is the red line at the right. The Balmer series includes the lines due to transitions from an outer orbit n > 2 to the orbit n' = 2. Named after Johann Balmer, who discovered the Balmer formula, an empirical equation to predict