Contemporary theories of structure and bonding in inorganic chemistry

4 Contemporary theories of structure and bonding in inorganic chemistry 

In this section, we survey the various theories of bonding and electronic structure which will be invoked elsewhere in the book and which will be regularly encountered by any serious student of inorganic chemistry. As pointed out in Section 1.2, it must be stressed that no one theory is wholly adequate, and the inorganic chemist must have at least a passing knowledge of several. The all-purpose theory would probably 

Almost simultaneous with the publication of Kossel s paper there appeared a rival electronic theory. The American chemist Lewis introduced the idea of the covalent electron-pair bond. Like Kossel, he was impressed by the apparent stability of the noble gas configuration. He was also impressed by the fact that, apart from many compounds of the transition elements, most compounds when rendered as molecules have even numbers of electrons, suggesting that electrons are usually found in pairs. Lewis devised the familiar representations of molecules and polyatomic ions (Lewis structures, or Lewis diagrams) in which electrons are shown as dots (or as noughts and crosses) to show how atoms can attain noble gas configurations by the sharing of electrons in pairs, as opposed to complete transfer as in Kossel s theory. It was soon apparent from the earliest X-ray studies that Kossel s theory was more appropriate 

The chief merit of the ionic theory is the ease with which quantitative calculations can be performed within a simple electrostatic approach. These will be discussed in Chapter 5. Even if it could be conclusively proven that crystals such as NaCl do not contain ions, chemists would be reluctant to discard the ionic description. The model even has successes-and this should arouse suspicion - in situations where few chemists would seriously entertain the real existence of ions. For example, the 4d and 5d elements tend to exhibit high oxidation states more readily than their counterparts in the 3d series. This can be explained if we note (see Section 4.3) that the energies required to attain highly ionised states are much smaller for the heavier atoms, provided that we are prepared to believe that compounds like WF6, Re03 and 0s04 are ionic  

Valence shell electron pair repulsion theory (VSEPR) 

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