Hydrogen is the lightest element in the periodic table with the symbol H and atomic weight 1. Its standard atomic weight is 1.008. In-universe, it is the most abundant element. Its electronic configuration is 1s1. It has three isotopes. The most common isotope is protium which has 1 proton and no neutron. The heavier elements were made from Hydrogen or from elements that were made from it. At STP, it is a highly combustible gas with molecular formula H2. Most of the hydrogen on Earth exists as water or organic compounds.
Robert Boyle described the reaction between acids & iron filings. This reaction resulted in the cause of H-gas. First Henry Cavendish recognized it as a discrete substance in 1766. He obtained the gas from a metal-acid reaction and named as “inflammable air”. He investigated that “inflammable air” was identical to a hypothetical substance known as phlogiston.
In 1781, he further found that the gas produces H2O when it fired. The element was named by Antoine Lavoisier in 1783 as hydrogen (hydro meaning “water” and genes meaning “forming”). Liquefaction of H was done by James Dewar for the first time in 1898. In 1783, Jacques Charles invented H-filled balloons for the first time.
It is highly combustible. Its enthalpy of combustion is −286 kJ/mole. The energy of the electron in a H atom in the ground is −13.6 eV which can be calculated accurately by using the Bohr model of the atom. H2 occurs in 2 isoforms. It forms compounds with elements that are more electronegative than hydrogen such as halogens. In the formation of these compounds, hydrogen takes on a partial positive charge. When hydrogen-bonded to a more electronegative element, particularly F, O, or N, hydrogen can form a hydrogen bond that is critical to the stability of many biological molecules. These compounds are called hydrides. Its oxidation gives hydrogen ions. This ion contains no electrons but a nucleus that consists of one proton. Therefore, H ion is often called a proton. This species is central to the discussion of the Brønsted–Lowry acid-base concept.
H has three naturally occurring isotopes. These isotopes are denoted as1H (protium), 2H(deuterium), and 3H(tritium). For deuterium and tritium, the symbols D and T are sometimes used. These symbols are accepted by IUPAC. But it is recommended to use the isotopic symbol to avoid confusion.
The most common H isotope with an abundance of more than 99.98% is protium which has 1 proton and no neutron. It is given the formal name protium because the nucleus of this isotope consists of only a single proton. Since the proton is never observed to decay, the protium is considered to be stable.
The other stable isotope of H is called deuterium which has one proton and one neutron in its nucleus. Harold Urey discovered the deuterium in 1931. It is thought that all deuterium in the universe has been produced at the time of the Big Bang. Water consists of deuterium instead of normal hydrogen, which is called heavy water.
The third isotope of H is called tritium which has one proton and two neutrons in its nucleus. Ernest Rutherford, Mark Oliphant, and Paul Harteck prepared Tritium in 1934. It is radioactive. It decays into helium-3 through -decay with a half-life of 12.32 years.
This reaction is the most convenient laboratory method for the preparation of hydrogen. Hydrogen gas can be prepared by the reaction of metals with acids. The rate of hydrogen evolution depends on the metal, the pH, and the presence of alloying agents. Hydrogen evolution can be induced by using acids.
Hydrogen evolution is slower in the absence of acid.
Metals like Al and Ga react with water slowly. It is because they form passivated coatings of oxides. However, their alloys do react with water. Al can produce hydrogen gas at high pH.
Water is the most abundant source of H. Passing steam over a coke at 1000˚C gives a mixture of CO and H2. The mixture of CO and H2 is called water gas. Water-gas is called industrial fuel.
Natural gas is also an important source of H2. At high temperatures, methane (natural gas) reacts with steam to produce a mixture of CO and H2.
Electrolysis of Water
The simplest method of producing H2 is the electrolysis of water. During this process, a low voltage current is passed through the water. Gaseous oxygen is formed at the anode while gaseous H is formed at the cathode.
It is used for refining petroleum, treating metals, producing fertilizer, and processing foods in industries. Petroleum industries use it to lower sulfur content in the fuel. H-filled balloons are used to gather information about atmospheric pressure, temperature, and wind speed. Liquid H is used as a fuel in many space rockets. H2O2 is used as a cleaner. It is used in a H bomb. It is because atoms of hydrogen fuse together to produce a lot of energy in explosions. H2 is used in fuel cells to produce electricity. In a fuel cell, it reacts with oxygen to produce electricity, water, and a small amount of heat. Many different devices use various types of fuel cells. It is used as a transportation fuel in vehicles using fuel cells. A fuel cell is more efficient than n internal combustion engine. Hydrogenation (addition of H2 ) is used on a large scale. The hydrogenation of nitrogen is used to produce ammonia in the Haber process. This hydrogenation process is used to convert unsaturated fats and oils into saturated fats and oils. So, this process finds its application in the production of margarine. Methanol is prepared by the hydrogenation of CO2. It is used in the manufacture of HCI. It finds its application in power stations as a coolant in generators. It is used as shielding gas in welding.