Hydrogen Hydrogen Hydrogen is a chemical element with symbol H and atomic number 1. With a standard atomic weight of , hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass. Non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed "protium" (name rarely used, symbol H), has one proton and no neutrons. The universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless,
The Periodic Table (short story collection) The Periodic Table (short story collection) The Periodic Table () is a collection of short stories by Primo Levi, published in 1975, named after the periodic table in chemistry. In 2006, the Royal Institution of Great Britain named it the best science book ever. The stories are autobiographical episodes of the author's experiences as a Jewish-Italian doctoral-level chemist under the Fascist regime and afterwards. They include various themes that follow a chronological sequence: his ancestry, his study of chemistry and practising the profession in wartime Italy, a pair of imaginative tales he wrote at that time, and his subsequent experiences