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==Chemical Properties==
==Chemical Properties==
At normal pressures hydrogen melts at 14.01[[Kelvin]] (K) and boils at 20.28K, 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 hypothesise 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>.
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 hypothesise 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 As a result of this it was used in many early airships and balloons, but due to the dangers involved it has been replaced by [[helium]] in these applications.
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 As a result of this it was used in many early airships and balloons, but due to the dangers involved it has been replaced by [[helium]] in these applications.