Isotopes, of hydrogen

Hydrogen as it occurs in nature is predominantly composed of atoms in which the nucleus is a single proton. In addition, terrestrial hydrogen contains about 0.0156% of deuterium atoms in which the nucleus also contains a neutron, and this is the reason for its variable atomic weight (p. 17). Addition of a second neutron induces instability and tritium is radioactive, emitting low-energy particles with a half-life of 12.33 y. Some characteristic properties of these 3 atoms are given in Table 3.1, and their implications for stable isotope studies, radioactive tracer studies, and nmr spectroscopy are obvious. 

In the molecular form, dihydrogen is a stable, colourless, odourless, tasteless gas with a very low mp and bp. Data are in Table 3.2 from which it is clear that the values for deuterium and tritium are substantially higher. 

6keV mean 5.7keV range in air 6mm range in water 6 um. 

Hydrogen has three isotopes H (hydrogen), jH (deuterium, symbol D), and fH (tritium, symbol T). The natural abundances of the stable hydrogen isotopes are hydrogen, 99.985 percent and deuterium, 0.015 percent. Tritium is a radioactive isotope with a half-life of about 12.5 years. 

Although D2O resembles H2O chemically in most respects, it is still a toxic substance. The reason is that deuterium is heavier than hydrogen, so its compounds often react more slowly than those of the lighter isotope. Drinking D2O instead of H2O on a regular basis could prove fatal because of the slower rate of transfer of D compared with that of H in the acid-base reactions involved in enzyme catalysis. This kinetic isotope effect is also manifest in acid ionization constants. For example, the ionization constant of acetic acid 

Hydrogenation is the addition of hydrogen to compounds containing multiple bonds, usually C=C and C=C bonds. A simple example of hydrogenation is the conversion of ethylene to ethane  

This reaction is quite slow under normal conditions, but the rate can be greatly increased by the presence of a catalyst such as nickel or platinum. 

Both deuterium and tritium can be incorporated into a variety of hydrogen-containing compounds and used to follow (or trac the course of reactions involving these compounds. For example, one can follow the rate of absorption and excretion of water in the body by using small amounts of D2O. Some D2O is almost immediately 

Deuterium-hydrogen exchange. The exchange of deuterium for hydrogen (o) in compounds containing a polar covalent H-X bond, where X = 0, N, S, F, Cl, Br, I, and (b) in compounds containing essentially nonpolar H-C bonds. 

All alkali metal hydrides (see Sections 9.7 and 10.4) crystallize with the NaCl lattice. From diffraction data and the ionic radii of the metal ions Appendix 6) the radius of can be estimated using equation 9.3 it varies from 130 pm (in LiH) to 154 pm (in CsH) and can be considered similar to that of F (133 pm). 

Hydrides of the s -block metals (excluding Be) can be made by heating the metal with H2. 

When we compare Aj77 for reaction 9.4 with those for the formations of F and CH from F2 and CI2 (—249 and —228kJmoP, respectively), we understand why, since H is about the same size as F, ionic hydrides are relatively unstable species with respect to dissociation into their constituent elements. Salt-like hydrides of metals in high oxidation states are most unlikely to exist. (More about binary hydrides in Section 9.7.) 

---

Caleulate the redueed mass of D Cl where D is the deuterium isotope of hydrogen (isotopie weight 2.014 atomie mass units) and Cl is the 35 isotope of ehlorine (isotopie weight 34.97 atomie mass units). 

The ordinary isotope of hydrogen, H, is known as Protium, the other two isotopes are Deuterium (a proton and a neutron) and Tritium (a protron and two neutrons). Hydrogen is the only element whose isotopes have been given different names. Deuterium and Tritium are both used as fuel in nuclear fusion reactors. One atom of Deuterium is found in about 6000 ordinary hydrogen atoms. 

Sometimes the strongly basic properties of Gngnard reagents can be turned to synthetic advantage A chemist needed samples of butane specifically labeled with deuterium the mass 2 isotope of hydrogen as shown... 

The three isotopes of hydrogen are almost indistinguishable for most chemical purposes, but a mass Spectrometer can see them as three different entities of mass 1, 2, and 3 Da. Isotopes of other elements can also be distinguished. Mass spectrometry is important for its ability to separate the isotopes of elements. 

A few natural isotopes are radioactive. Of the three isotopes of hydrogen, only that of mass 3 (tritium) i.s radioactive. Radioactive isotopes can be examined by other instrumental means than mass spectrometry, but these other means cannot see the nonradioactive isotopes and are not as versatile as a mass Spectrometer. 

Tables 2,3, and 4 outline many of the physical and thermodynamic properties ofpara- and normal hydrogen in the sohd, hquid, and gaseous states, respectively. Extensive tabulations of all the thermodynamic and transport properties hsted in these tables from the triple point to 3000 K and at 0.01—100 MPa (1—14,500 psi) are available (5,39). Additional properties, including accommodation coefficients, thermal diffusivity, virial coefficients, index of refraction, Joule-Thorns on coefficients, Prandti numbers, vapor pressures, infrared absorption, and heat transfer and thermal transpiration parameters are also available (5,40). Thermodynamic properties for hydrogen at 300—20,000 K and 10 Pa to 10.4 MPa (lO " -103 atm) (41) and transport properties at 1,000—30,000 K and 0.1—3.0 MPa (1—30 atm) (42) have been compiled. Enthalpy—entropy tabulations for hydrogen over the range 3—100,000 K and 0.001—101.3 MPa (0.01—1000 atm) have been made (43). Many physical properties for the other isotopes of hydrogen (deuterium and tritium) have also been compiled (44).

Thermodynamic Properties. Ordinary water contains three isotopes of hydrogen [1333-74-0] (qv), ie, H, H, and H, and three of oxygen [7782 4-7] (qv), ie, O, and The bulk of water is composed of and O. Tritium [15086-10-9] H, and are present only in extremely minute concentrations, but there is about 200-ppm deuterium [16873-17-9], H, and 1000-ppm in water and steam (see Deuterium and tritium). The thermodynamic properties of heavy water are subtly different from those of ordinary water. lAPWS has special formulations for heavy water. The properties given herein are for ordinary water having the usual mix of isotopes. 

Isotopic Exchange Reactions. Exchange reactions between the isotopes of hydrogen are well known and well substantiated. The equihbrium constants for exchange between the various hydrogen molecular species have been documented (18). Kinetics of the radiation-induced exchange reactions of hydrogen, deuterium, and tritium have been critically and authoritatively reviewed (31). The reaction T2 + H2 — 2HT equiUbrates at room temperature even without a catalyst (30). 

Tritium differs from the other two isotopes of hydrogen in being radioaetive and this immediately indieates its potential uses and its method of deteetion. Tritium oeeurs naturally to the extent of about 1 atom per 10 hydrogen atoms as a result of nuelear reaetions indueed by eosmie rays in the upper atmosphere ... 

It IS often stated that unclear fusion tvill produce no radioactive hazard, but this is not correct. The most likely fuels for a fusion reactor would be deuterium and radioactive tritium, which arc isotopes of hydrogen. Tritium is a gas, and in the event of a leak it could easily be released into the surrounding environment. The fusion of deuterium and tritium produces neutrons, which would also make the reactor building itself somewhat radioactive. However, the radioactivity produced in a fusion reactor would be much shorter-lived than that from a fission reactor. Although the thermonuclear weapons (that use nuclear fusion), first developed in the 1950s provided the impetus for tremendous worldwide research into nuclear fusion, the science and technology required to control a fusion reaction and develop a commercial fusion reactor are probably still decades away. 

The most plausible fusion reaction for producing energy commercially involves two isotopes of hydrogen, deuterium (D) and tritium (T), or H and H. Deuterium contains one proton and one neutron for an atomic number of two. Tritium contains one proton and two neutrons for an atomic number of three. The reaction is... 

The amino acid methionine is formed by a melhylation reaction of homo cysteine with iV-methyltetrahydrofolate. The stereochemistry of the reactior has been probed by carrying out the transformation using a donor with a "chiral methyl group" that contains protium (H), deuterium (D), and tritium (T isotopes of hydrogen. Does the methylation reaction occur with inversion oi retention of configuration ... 

The nuclear symbols for the isotopes of hydrogen and uranium referred to above are... 

Because isotopes of the same element have the same number of protons and the same number of electrons, they have essentially the same chemical and physical properties. However, the mass differences between isotopes of hydrogen are comparable to the masses themselves, leading to noticeable differences in some physical properties and slight variations in some of their chemical properties. Hydrogen has three isotopes (Table B.2). The most common ( H) has no neutrons so its nucleus is a lone proton. The other two isotopes are less common but nevertheless so important in chemistry and nuclear physics that they are given special names and symbols. One isotope (2H) is called deuterium (D) and the other ( H) is called tritium (T). 

The two most common isotopes of oxygen are and 0, and the two natural isotopes of hydrogen are and or D (deuterium). If a sample of carbonate contains Cis moles of and Ci6 moles of then define the heavy light ratio as Ris = Cia/Cie- Similarly, natural water molecules are mostly of three types H O, H] 0, and HD O. For a given sample of water, call the number of moles of each W, W g, and Wq, respectively. Then define the heavyriight ratios as ki8 = Wig/VV and Rp = WqIW. For either water or carbonate, the 5 are defined as deviations of these ratios from standard values for these ratios (call the ratios of the standards Sig and Sq) ... 

Gat, J.R. 1980 The isotopes of hydrogen and oxygen in precipitation. In Fritz, P. and Fontes, J., eds.. Handbook of Environmental Isotope Geochemistry. Amsterdam, Elsevier 21-47. 

The ratios of heavy to light stable isotopes of hydrogen H/iH (or D/H), carbon i C/i C, nitrogen oxygen i 0/i 0, and sulfur 3 5/325 show distinctive patterns of... 

Because isotopes of hydrogen have the smallest possible... 

Some nuclear reactors use heavy water to slow down neutrons produced during nuclear fission. Heavy water contains deuterium, an isotope of hydrogen. What is the mass number of deuterium ... 

---