Chapter 10: Hydrogen

Hydrogen exists in three naturally occurring isotopes—protium, deuterium, and tritium—with distinct nuclear properties that have profound implications for nuclear magnetic resonance spectroscopy, kinetic isotope effects, and nuclear fusion reactions. The fundamental duality of hydrogen is emphasized: functioning as a proton, it represents the ultimate Lewis acid capable of accepting electron density, while as a hydride ion, it serves as a powerful Lewis base and electron donor. Dihydrogen gas holds significance both as a potentially transformative clean fuel for future energy systems and as an indispensable industrial chemical used in ammonia synthesis through the Haber process, catalytic hydrogenation reactions, and methanol production. The chapter provides comprehensive coverage of hydrogen production methods, ranging from simple laboratory preparations involving acids and alkalis to large-scale industrial processes including steam reforming of natural gas, coal gasification, water electrolysis, and emerging renewable technologies such as biohydrogen generation and photoelectrochemical water splitting. The reactivity of dihydrogen encompasses radical chain mechanisms with oxygen and halogens, catalytic activation at metal surfaces, and coordination to transition metals as η²-ligands in organometallic chemistry. Hydrogen compounds are systematically organized into three categories: molecular hydrides, further subdivided into electron-precise, electron-rich, and electron-deficient species with diborane exemplifying complex three-center bonding; saline hydrides such as lithium hydride and calcium hydride that function as ionic compounds and hydride transfer reagents; and metallic hydrides of transition and lanthanide elements exhibiting variable stoichiometry and hydrogen mobility relevant to energy storage applications. The chapter emphasizes hydrogen bonding as a critical intermolecular force stabilizing water, biological macromolecules, and crystalline hydrate structures. Advanced topics include nickel-metal hydride battery technology, reversible hydrogen storage in lightweight compounds, and catalytic activation mechanisms involving oxidative addition and metal-hydride clusters. Synthetic strategies for preparing hydrogen compounds include direct combination reactions, protonation pathways, and metathesis reactions with strong hydride donors such as lithium aluminum hydride and sodium borohydride.