The Chemistry of Hydrogen

Hydrogen is the most abundant of all the elements 90-95% of the atoms or atomic nuclei in the universe are believed to be those of hydrogen. One sign of this abundance is the energy that we receive from the Sun. This is supplied by a sequence of nuclear fusion reactions in which hydrogen ( H) is converted into helium ( He). In the Sun, some 600 million tonnes of hydrogen are consumed every second in this way. 

The situation is rather different on Earth, where hydrogen is only the ninth most abundant element by mass in the Earth s crust, oceans and atmosphere, and the fourth most common type of atom. Nevertheless, it seems especially plentiful because it is available in highly accessible forms such as water and the hydrocarbons present in natural gas and crude oil. 

The major industrial source of hydrogen gas is the reaction of methane with water at high temperatures (800-1000°C) and pressures (10-50 atm) in the presence of a metallic catalyst (often nickel)  

Large quantities of hydrogen are also formed as a by-product of gasoline production, when hydrocarbons with high molecular masses are broken down (or cracked) to produce smaller molecules more suitable for use as a motor fuel. 

Copyright 2010 Cengage Learning, Inc. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. 

Very pure hydrogen can be produced by the electrolysis of water (see Section 18.7), but this method is currently not economically feasible for large-scale production because of the relatively high cost of electricity. 

Boiling points of covalent hydrides were discussed in Section 16.1. 

The third class of hydrides is the metallic, or interstitial, hydrides, which are formed when transition metal crystals are treated with hydrogen gas. The hydrogen molecules dissociate at the metal s surface, and the small hydrogen atoms migrate into the crystal structure to occupy holes, or interstices. These metal-hydrogen mixtures are more like solid solutions than true compounds. Palladium can absorb about 900 times its own volume of hydrogen gas. In 

TABLE 18.6 Selected Reactions of the Alkali Metals Reaction Comment 

TABLE 18.5 Types of Compounds Formed by the Alkali Metals with Oxygen 

The alkali metal ions are very important for the proper functioning of biological systems, such as nerves and muscles Na+ and K+ ions are present in all body cells and fluids. In human blood plasma the concentrations are 

Since the concentrations are so different inside and outside the cells, an elaborate mechanism involving selective ligands is needed to transport Na+ and K+ ions through the cell membranes. 

Recently, studies have been carried out concerning the role of the Li+ ion in the human brain, and lithium carbonate has been used extensively in the treatment of manic-depressive patients. The Li+ ion apparently affects the levels of neurotransmitters, molecules that assist the transmission of messages along the nerve networks. Incorrect concentrations of these molecules can lead to depression or mania. (See Section 12.16 for a brief discussion of lithium s role in biological systems.) 

Element Ionization Energy (kj/mol) Standard Reduction Potential (V) for M+ + e- M Radius of M (pm) Melting Point (°C) 

Unless otherwise noted, all art on this page is O Cengage Learning 2014. 

---

Perhaps the most exciting recent development in the chemistry of hydrogen is the discovery that, in transition metal polyhydrides, the molecule Hj can act as a dihapto ligand, (see below). 

An overall view of the chemistry of hydrogen requires that it be classified alone—as a separate... 

In another experiment, naphthalene-d8 was used to investigate the chemistry of hydrogen transfer between coal and nondonor solvent at 380°C. An analysis of the recovered naphthalene-d8 showed that approximately 4% of the hydrogen in the coal and in the naph-thalene-d8 exchanged. Most of the protium incorporated in the naphthalene-d8 was found in the a-position. The coal products contained approximately 2 wt % chemically-bound napththalene-d8. 

The main part of this research deals with the reaction of deuterium gas and Tetralin-d12 with a bituminous coal. In a separate experiment, naphthalene-d8 was used for investigating the chemistry of hydrogen transfer between coal and a nondonor solvent. In each experiment, the coal products and spent solvent were analyzed for toal deuterium content and for deuterium incorporation in each structural position. 

Boland, J. J. (1992a). Role of bond-strain in the chemistry of hydrogen on the Si(lOO) surface. Surf. Sci. 261, 17-28. 

In this chapter, we ll take a detailed look at the chemistry of hydrogen and oxygen, and we ll discuss some of the properties of water, the solvent for all the reactions to be discussed in Chapters 15 and 16. 

Deuterium (D) is the hydrogen isotope of mass number 2, with a proton and a neutron in its nucleus. The chemistry of deuterium is nearly identical to the chemistry of hydrogen, except that the C — D bond is slightly stronger than the C—H bond by 5.0 kJ/mol (1.2 kcal/mol). Reaction rates tend to be slower if a C —D bond (as opposed to a C—H bond) is broken in a rate-limiting step. 

King, R. B. (1995). Inorganic Chemistry of the Main Group Elements. New York VCH Publishers. An excellent introduction to the descriptive chemistry of many elements. Chapter 1 deals with the chemistry of hydrogen. 

The chemistry of hydrogen peroxide and Caro s acid can be used in many applications involving metals metal extraction and separation from ores or waste, hydrometallurgy, and surface treatment of metals and alloys. Compared to alternative treatments, the direct chemical costs are sometimes higher, but the difference is often outweighed by advantages in simplicity of operation (cost savings on equipment), and in lower overall effluent production. 

The chemistry of hydrogen depends mainly on three electronic processes ... 

The variety in the mode of reaction of hydrogen peroxide makes it essential that a detailed kinetic study of any system should be made before any conclusions are drawn about a reaction mechanism and justifies the statement by W. D. Bancroft (5) that . . . the chemistry of hydrogen peroxide is a hopeless subject for the phenomenological or Baconian experimenter because misleading experiment is everywhere. ... 

The hydrogen sulfide present in natural gas, SNG, town gas, and synthesis gas must be removed for the sake of product gas quality. Hence, technology for removing hydrogen sulfide from gases has been extensively developed and is itself the subject of a voluminous literature (71, 72). From the standpoint of economic recovery of sulfur, the chemistry of hydrogen sulfide is substantially more tractable than that of sulfur dioxide. For the most part, these processes are not within the chosen scope of the present paper. 

By definition, the potential of this system is zero (E° = 0.000 V) at all temperatures when an inert metallic electrode dips into a solution of hydrogen ions of unit activity (i.e., pH = 0) in equilibrium with H2 gas at 1 atm pressure. The potentials of all other electrodes are then referred to this defined zero. However, the absolute potentials of other electrodes may be either greater or smaller, and thus some must have positive and others negative potentials relativeto the standard hydrogen-electrode.-While this-subject is -not properly an aspect of the chemistry of hydrogen, it will be briefly discussed here as a matter of convenience. 

Morse, J.W., Millero, F.J., Cornwell, J.C., Rickard, D, 1987. The chemistry of hydrogen sulfide and iron sulfide systems in natural waters. Earth-Sci. Rev. 24, 1 2. 

---