water molecules

Hydrogen is a chemical element with the symbol H (for Latin hydrogenium “water maker”) and the atomic number 1. In the periodic table, the element hydrogen is in the 1st period and in the 1st IUPAC group. With a mass fraction of around 70%, hydrogen is the most common chemical element in the universe, but not on Earth, where its mass fraction of the earth's shell is only 0.87%. The majority of hydrogen on Earth is bound in water, the compound with oxygen, the mass of which consists of 11% hydrogen. Hydrogen is bound to other elements in all plants and living organisms and in addition, the element hydrogen is a component of almost all chemical substances with which organic hydrogen is the chemical element with the lowest atomic mass. Its most abundant isotope does not contain a neutron, but consists of just one proton and one electron. There are two other naturally occurring isotopes of hydrogen, of which the non-radioactive deuterium accounts for 0.0156% of natural hydrogen, while the radioactive tritium formed in the upper layers of the atmosphere only occurs in very small amounts. Under conditions that normally prevail on Earth (see standard conditions), the gaseous element hydrogen is not present as atomic hydrogen with the symbol H, but as molecular hydrogen with the symbol H2, as a colorless and odorless gas. For example, when new hydrogen is formed during redox reactions, the element temporarily occurs atomically as H and is referred to as nascent hydrogen. In this reactive form, hydrogen reacts particularly well with other compounds or elemental chemistry and biochemistry. (Source Wikipedia)