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Hydrogen fluoride is lighter than air and could theoretically be used as a lifting gas. However, it is extremely corrosive, highly toxic, expensive, is heavier than other lifting gases, and has a low boiling point of 19.5 °C. Its use would therefore be impractical.
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.
Because of its flammability, liquid hydrogen should be kept away from heat or flame unless ignition is intended. Unlike ambient-temperature gaseous hydrogen, which is lighter than air, hydrogen recently vaporized from liquid is so cold that it is heavier than air and can form flammable heavier-than-air air–hydrogen mixtures.
Since hydrogen is a lighter-than-air gas, it collects under roofs and overhangs (typically referred to as trapping sites), where it forms an explosion hazard. [14] Many individuals are familiar with protecting plants from heavier-than-air vapors, but are unfamiliar with "looking up", and is therefore of particular note. [33]
It is also called "hydrogen burning", which should not be confused with the chemical combustion of hydrogen in an oxidizing atmosphere. There are two predominant processes by which stellar hydrogen fusion occurs: proton–proton chain and the carbon–nitrogen–oxygen (CNO) cycle.
Heavier elements were mostly produced much later, in stellar nucleosynthesis. Hydrogen and helium are estimated to make up roughly 74% and 24% of all baryonic matter in the universe respectively. Despite comprising only a very small fraction of the universe, the remaining "heavy elements" can greatly influence astronomical phenomena.
The weight of a heavy water molecule, however, is not very different from that of a normal water molecule, because about 89% of the mass of the molecule comes from the single oxygen atom rather than the two hydrogen atoms. Heavy water is not radioactive. In its pure form, it has a density about 11% greater than water but is otherwise physically ...
Oxygen gas can also be produced through electrolysis of water into molecular oxygen and hydrogen. DC electricity must be used: if AC is used, the gases in each limb consist of hydrogen and oxygen in the explosive ratio 2:1. A similar method is the electrocatalytic O 2 evolution from oxides and oxoacids.