Beryllium incomplete octets

The octet rule is remarkable in its ability to realistically model bonding and structure in covalent compounds. But, like any model, it does not adequately describe all systems. Beryllium, boron, and aluminum, in particular, tend to form compounds in which they are surrounded by fewer than eight electrons. This situation is termed an incomplete octet. Other molecules, such as nitric oxide ... 

In the beryllium chloride molecule (BeCl2(g)), the beryllium atom has only four electrons in its valence shell (Figure 4-31). The molecule is described as electron deficient. The boron trichloride molecule is also electron deficient the central boron atom has only six electrons in its valence shell (Figure 4-32). A related example of an electron-deficient molecule is aluminium trichloride, AICI3. The aluminium atom has only six electrons in its valence shell. All these molecules have incomplete octets. 

Beryllium compounds, such as BeH2, also have incomplete octets. 

I Beryllium often forms incomplete octets, as I It does In this structure. 

The number of species with incomplete octets is limited to some beryllium, boron, and aluminum compounds. Perhaps the best examples are the boron hydrides. Bonding in the boron hydrides will be discussed in Chapter 22. 

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See also in sourсe #XX -- [ , ]

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