Hydrogen
chemical element with symbol H and atomic number 1; lightest and most abundant substance in the universe / From Wikipedia, the free encyclopedia
Hydrogen is a chemical element at the start of the periodic table. It has the symbol H and atomic number 1. It also has a standard atomic weight of 1.008. This makes it the lightest element in the periodic table. In standard conditions, hydrogen is a diatomic gas with the formula H
2, or dihydrogen.[8] In this state, hydrogen is also called hydrogen gas or molecular hydrogen. Hydrogen has no color, smell, or taste.[9] Hydrogen is not toxic and is very combustible.[8]
Hydrogen is the most common chemical element in the universe. Hydrogen is almost 75% of all normal (baryonic) matter by mass.[10] Most stars are made of mostly hydrogen. Hydrogen stars are made of hydrogen in a plasma state. On Earth, hydrogen is seen in water and organic compounds. Hydrogen's most common isotope has one proton and no neutrons. This isotope also has one electron orbiting around it.
Hydrogen began to form a second after the Big Bang. These hydrogens did not have any neutrons or electrons. The first neutral hydrogen with an electron would not form until 380,000 years later during the recombination epoch, when the universe was cold enough for hydrogens to attract electrons.[11]
Hydrogen is usually nonmetallic and can form covalent bonds with most nonmetals. These covalent bonds can create molecules such as water and other organic substances. Hydrogen is the main part of acid–base reactions. These reactions exchange protons in soluble molecules. In ionic compounds, ions can either be anions or cations. Hydrogen anions are negatively charged and are called hydrides. Hydrogen cations are positively charged and are written as H+
. Cations are also called protons (symbol p), because they are only made of a proton and nothing else.
Hydrogen gas was first made artificially in the 1700s. Henry Cavendish identified hydrogen gas as a distinct substance between 1766 and 1781.
Most hydrogen production is from steam reforming natural gas. Hydrogen has many industrial uses. Hydrogen can be used to process fossil fuels, hydrocrack, and produce ammonia.