View source for Hydrogen

{{Element 
| name= Hydrogen
| caption=
| symbol=H
| class=Group 1
| amass=1.001
| anumber=1
| stableisotopes=
| unstableisotopes=
| meltingpoint=−259.16
| boilingpoint=−252.879
| density=0.08988
| hardness=
| abundance=0.0000005
| oxidation=-1, +1
| date=1766
| discname=[[Henry Cavendish]]
| origname=
| uses=
| obtained=
}}
'''Hydrogen''' is the most abundant of all the [[element]]s,<ref>Hydrogen makes up roughly 75% of the matter in the [[universe]].</ref> and has the [[chemical symbol]] H and an [[atomic number]] of 1. Despite this abundance, naturally occurring elemental hydrogen is extremely rare on [[Earth]].

==Chemical Properties==

At normal pressures hydrogen melts at 14.01 [[Kelvin]] (K) and boils at 20.28 K, essentially meaning that it only exists on Earth as a gas. The near-vacuum of interstellar space means that hydrogen is also a gas under these circumstances. Astronomers and chemists hypothesize that hydrogen exists as a plasma inside stars and possibly in a metallic form in the cores of gas giant [[planets]] such as [[Jupiter]]. The most common form of hydrogen is molecular hydrogen, consisting of two atoms bonded by a single covalent bond. The chemical symbol for molecular hydrogen is H<sub>2</sub>.

Due to having the lowest possible atomic number hydrogen is the lightest element. As a result of this it was used in many early airships and balloons, but due to the dangers involved with its flammability, it has been replaced by [[helium]] in these applications.

==Isotopes==
The most common form of hydrogen is protium, although this name is rarely used and it is generally known simply as hydrogen.  Protium [[atom]]s consist of a single [[proton]] orbited by a single [[electron]]. Two other hydrogen [[isotopes]] are known to exist: [[deuterium]], which has one neutron and an atomic weight of 2, and [[tritium]] with two neutrons and an atomic weight of 3. [[Tritium]] is [[radioactive]], with a [[half-life]] of 12.32 years. Naturally occurring tritium is extremely rare on Earth; it is manufactured in nuclear reactors and is therefore extremely expensive.  It has a number of valuable applications, such as light-emitting inserts for optical instruments and emergency equipment.

==Compounds==
Hydrogen can be found in the vast majority of [[organic]] compounds, as well as many [[inorganic]] compounds.<ref>For example, [[hydrocarbon]]s and metal hydrides, respectively</ref> It is an important component of [[water]] and most [[acid]]s because water has a chemical formula of H<sub>2</sub>O and acids donate hydrogen atoms when they react with water.<ref>https://www.britannica.com/science/acid</ref>

==Occurrence in Nature==

Hydrogen makes up 75% of all matter in the universe by mass. Well over 90% of all atoms in the universe are hydrogen. It is the main element found in [[stars]] and gas-giant (Jovian) planets. Huge clouds of molecular hydrogen are found in interstellar space; astronomers believe that these clouds are associated with star formation, with the hydrogen providing the raw material and fuel for stars to form. The timescale required for this to occur is estimated to be around 100,000 years for a star the size of the [[Sun]].  This means that, like other cosmic processes, some of which take millions or billions of years, the process of star formation cannot be observed directly. However, stars in various phases of the process are abundant, and the process is well established.  Young-Universe Creationists reject all of this.

==Fuel for vehicles==
Hydrogen is one of two fuels needed for [[fuel cell]]s (the other being oxygen), which have the potential to be a major form of alternative energy in the future. Fuel cells are very clean energy sources; their only by-products are [[water]] and heat. Since no [[pollutant]]s or [[greenhouse gas]]es are produced, the use of fuel cells could provide cleaner air in larger cities.{{fact}}

Unfortunately, hydrogen is not a viable fuel source at present. Today's average car, for example, would require an unfeasibly large fuel tank to carry enough hydrogen for practical purposes. Hydrogen is also extremely [[flammable]] and suitable safeguards are needed to reduce the chances of a fatal explosion in an accident.  There is also the issue of obtaining the pure hydrogen needed.  Hydrogen can be obtained from distilled water through electrolysis, but this requires the same amount of energy the Hydrogen's use in a fuel cell would yield.  Fuel cells would not solve the eventual energy crisis; it would simply move the problem to the power plants providing the energy to obtain the hydrogen through electrolysis.{{fact}}

If hydrogen could be used in cars, it would be important in establishing the [[hydrogen economy]].

As free hydrogen does not exist on Earth, hydrogen is not actually a source of energy but rather a carrier of it: its value as a fuel is that it provides a clean and efficient way to use energy produced by some other source. Due to the Second Law of thermodynamics the energy used to produce free hydrogen must be at least equal to the energy contained within it, meaning that at present it is not a viable fuel for most applications. Potential solutions include the use of bacteria that produce hydrogen through photosynthesis, which would effectively allow solar energy to be stored in hydrogen and used as fuel.<ref>http://www.making-hydrogen.com/hydrogen-from-bacteria.html</ref>

==Notes and references==
<references/>

{{Periodic table}}