The Solid State Structure, Properties, and Bonding

The large spaces within ice give the solid state a lower density than the liquid state. When the surface of a lake freezes in winter, the ice floats on the liquid water below. If the solid were denser than the liquid, as is true for nearly every other substance, the surface of a lake would freeze and sink repeatedly until the entire lake was solid. As a result, aquatic plant and animal life would not survive from year to year. 

The density of water changes in a complex way. When ice melts at 0°C, the tetrahedral arrangement around each O atom breaks down, and the loosened molecules pack much more closely, filling spaces in the collapsing solid structure. As a result, water is most dense (1.000 g/mL) at around 4°C (3.98°C). With more heating, the density decreases through normal thermal expansion. 

Stroll through the mineral collection of any school or museum, and you ll be struck by the extraordinary variety and beauty of these solids. In this section, we first discuss the general structural features of crystalline solids and then examine a laboratory method for studying them. We survey the properties of the major types of solids and find the whole range of intermolecular forces at work. We then present a model for bonding in solids that explains many of their properties. 

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The Solid State Structure, Properties, and Bonding Structixal Featxes of Solids Crystalline Solids Amorphous SoWs Bondrig in Sofids... 

As one might expect there is an approximate correlation between the solid state structure and the physical properties of a particular silicate. For instance, cement contains discrete 8104 units and is soft and crumbly asbestos minerals contain double chains of 8104 units and are characteristically fibrous mica contains infinite layers of 8104 units, the weak bonding between the layers is easily broken, and micas show cleavage parallel to the layers and granite contains feldspars that are based on three-dimensional 8104 frameworks and are very hard. 

In the series of the binary halides of selenium and tellurium, the crystal structure determinations of tellurium tetrafluoride (100) and of tellurium tetrachloride on twinned crystals (65, 66) were the key to understanding the various and partly contradictory spectroscopic and other macroscopic properties (e.g., 66,161,168,169,219,220, 412), as well as the synthetic potential of the compounds. In contrast to the monomeric molecular i//-tbp gas phase structures with C2v symmetry (417), the solid state structures of both are polynuclear. As the prototype of the chlorides and bromides of selenium and tellurium, crystalline tellurium(IV) chloride has a cubane-like tetrameric structure with approximate Td symmetry (Fig. 1). Within the distorted TeCla+a octa-hedra the bonds to the triply bridging chlorine ligands are much longer than to the terminal chlorines. The bonding system can be described either covalently as Te4Cli6 molecules, or, in an ionic approximation, as [(TeCl Cn4] with a certain degree of stereochemical activity of the lone pairs toward the center of the voluminous cubane center (65, 66). 

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