Bonding and structural trends within the elements

We will see that the bonding in tungsten arises from the strong unsaturated covalent bonds between the valence 5d orbitals. 

Regarding the structural trends in Table 1.1 we would like theory to be able to explain at least the following  

on the broad scale the change from close-packed structures on the left-hand side and middle of the periodic table to the more open structures on the right-hand side  

the 8-N rule which gives the number of neighbours expected for N 4  

the exceptions to the 8-N rule in particular the fact that the most stable form of carbon is graphitic (30 lead is fee (12), and nitrogen and oxygen are dimeric (1)  

---