Hydrogen - Hydrogen Is Everywhere, The Element, Discovery And Preparation, Uses Of Hydrogen, Hydrogen Disasters

Hydrogen is the chemical element of atomic number 1. Its symbol is H, it has an atomic weight of 1.008, its specific gravity at 32°F (0°C) is 0.0000899, and it melts at -434.7°F (-259.3°C). The boiling point of hydrogen is -423.2°F (-252.9°C), just above absolute zero. Boiling liquid hydrogen is the coldest substance known, with the exception of liquid helium. At room temperature, hydrogen is a colorless, odorless, tasteless gas. It consists of two stable isotopes of mass numbers 1 and 2.

Hydrogen is "number one" among the chemical elements. That is, it is the element whose atomic number is one. Its atoms are the simplest and lightest of all. A hydrogen atom contains only one electron, and it has a nucleus that consists of nothing but a proton. (A small percentage of hydrogen nuclei also contain one or two neutrons; see below.) In the periodic table, it is in a class by itself; there are no other members of its exclusive "group." It is usually placed at the top, all by itself.

Hydrogen's name is a clue to its most important position among the world's elements. It comes from the Greek hydro, meaning water, and genes, meaning born or formed. Hydrogen is a substance that gives birth to water (with a little help from oxygen). The name was coined in 1783 by the French chemist Antoine Lavoisier (1743-1794) in honor of the fact that when hydrogen burns in air it reacts with oxygen to form water, H₂O.