Triple bonds, heavier main group elements

Molecules of heavier main-group elements show significant differences to compounds of elements from the first-octal row of the periodic system. The coordination number of the lighter elements is rarely larger than 4 while many stable molecules of the heavier elements with coordination number 5 and 6 are known. Another difference concerns the stability of molecules with multiple bonds. Many stable molecules with double or triple bonds between the lighter elements are well known, particularly compounds that have C=C, C=N, C=0,... 

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