Ice, hydrogen bonding

The most striking feature of the earth, and one lacking from the neighboring planets, is the extensive hydrosphere. Water is the solvent and transport medium, participant, and catalyst in nearly all chemical reactions occurring in the environment. It is a necessary condition for life and represents a necessary resource for humans. It is an extraordinarily complex substance. Stmctural models of Hquid water depend on concepts of the electronic stmcture of the water molecule and the stmcture of ice. Hydrogen bonding between H2O molecules has an effect on almost every physical property of Hquid water. 

A tunneling junction device was used to determine the water structure at the mercury electrode in an aqueous solution of 0.25MHg2 (N03)2 + 0.3M HNO3. It was found that the structure of water domains is the same as that of hexagonal ice. Hydrogen bonding is a dominant, structuredetermining factor in liquid water near the mercury electrode surface. ... 

Figure 1.11. Structure of Ice. Hydrogen bonds (shown as dashed lines) are formed between water molecules.

In ice, hydrogen-bonding between molecules leads to the formation of a five-molecule structural unit, which is approximately tetrahedral (Fig. 3.4b). Each oxygen atom is surrounded by four others at a distance of 2.75 A three of them are in the same layer (forming, with other water molecules, puckered six-membered rings) and the fourth is in an adjacent layer. Large polyhedral cavities lie between these layers. 

Now consider the phases of water. In ice, hydrogen bonding leads to the rigid structure shown in T Figure 19.9. Each molecule in the ice is free to vibrate, but its translational and rotational motions are much more restricted than in liquid water. Although there are hydrogen bonds in liquid water, the molecules can more readily move about relative to... 

Figure 2.6. The tetrahedral structures of ice (a), (fc) are planes through sheets of selected oxygen nuclei (open circles), hydrogen nuclei (shotm in the insert as solid circles) are not shown in the main drawing. The insert illustrates the overlap of oxygen line pairs and the hydrogen nuclei, thus forming the hydrogen bonds (dotted lines)...

Upon melting, ice loses its open structure with the "melting" of some fraction of the hydrogen bonds, and so the volume of the Hquid water decreases, reaching a minimum at 4°C above this temperature thermal expansion dominates the density. 

Fig. 5. (a) Hydrogen-bonded open tetrahedral stmcture of ice (4) (b) Frank-Wen flickering cluster model of Hquid water (5). 

Thermodynamic and physical properties of water vapor, Hquid water, and ice I are given ia Tables 3—5. The extremely high heat of vaporization, relatively low heat of fusion, and the unusual values of the other thermodynamic properties, including melting poiat, boiling poiat, and heat capacity, can be explained by the presence of hydrogen bonding (2,7). 

Color from Vibrations and Rotations. Vibrational excitation states occur in H2O molecules in water. The three fundamental frequencies occur in the infrared at more than 2500 nm, but combinations and overtones of these extend with very weak intensities just into the red end of the visible and cause the blue color of water and of ice when viewed in bulk (any green component present derives from algae, etc). This phenomenon is normally seen only in H2O, where the lightest atom H and very strong hydrogen bonding combine to move the fundamental vibrations closer to the visible than in any other material. 

Fig. 4.10. The arrangement of H2O molecules in the common form of ice, showing the hydrogen bonds. The hydrogen bonds keep the molecules well apart, which is why ice has a lower density than water.

The crystal structure of many compounds is dominated by the effect of H bonds, and numerous examples will emerge in ensuing chapters. Ice (p. 624) is perhaps the classic example, but the layer lattice structure of B(OH)3 (p. 203) and the striking difference between the a- and 6-forms of oxalic and other dicarboxylic acids is notable (Fig. 3.9). The more subtle distortions that lead to ferroelectric phenomena in KH2PO4 and other crystals have already been noted (p. 57). Hydrogen bonds between fluorine atoms result in the formation of infinite zigzag chains in crystalline hydrogen fluoride... 

Gas hydrates are an ice-like material which is constituted of methane molecules encaged in a cluster of water molecules and held together by hydrogen bonds. This material occurs in large underground deposits found beneath the ocean floor on continental margins and in places north of the arctic circle such as Siberia. It is estimated that gas hydrate deposits contain twice as much carbon as all other fossil fuels on earth. This source, if proven feasible for recovery, could be a future energy as well as chemical source for petrochemicals. 

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