| Symbol | H |
| Atomic number | 1 |
| Group | 1 (Alkali metal) |
| Period | 1 |
| Block | s |
| Classification | Nonmetal |
| Appearance | Colorless gas |
| Color | Colorless |
| Number of protons | 1 p+ |
| Number of neutrons | 0 n0 |
| Number of electrons | 1 e- |
| Phase at STP | Gas |
| Density | 0.08988 g/cm3 |
| Atomic weight | 1.0079 u |
| Melting point | 13.99 K -259.16 °C -434.488 °F |
| Boiling point | 20.271 K -252.879 °C -423.1822 °F |
| Heat of vaporization | 0.4581 kJ/mol |
| Electronegativity (Pauling Scale) | 2.2 |
| Electron affinity | 72.769 kJ/mol |
| Oxidation states | −1, +1 (an amphoteric oxide) |
| Ionization energies |
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| Discovery and first isolation | Henry Cavendish (1766) |
| Named by | Antoine Lavoisier (1783) |
Discovery of hydrogen In 1671, Robert Boyle discovered and described the reaction between iron filings and dilute acids, which results in the production of hydrogen gas. In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, by naming the gas from a metal-acid reaction "inflammable air". He speculated that "inflammable air" was in fact identical to the hypothetical substance called "phlogiston" and further finding in 1781 that the gas produces water when burned. He is usually given credit for the discovery of hydrogen as an element. In 1783, Antoine Lavoisier gave the element the name hydrogen (from the Greek ὑδρο- hydro meaning "water" and -γενής genes meaning "former") when he and Laplace reproduced Cavendish's finding that water is produced when hydrogen is burned. | |