The heavier an element is in its group, the larger its atom and the weaker the hold the nucleus has on its only outside electron. 

   The most furious in the kingdom of nonmetals is fluorine. It has seven electrons in its "outer sphere." All it needs for complete bliss is an eighth electron. And it grabs it greedily from almost any other element of the Periodic System; nothing can resist fluorine's mad onslaught.

   The other nonmetals also accept electrons, some of them more, others less easily. And now we can understand why they are grouped mainly in the upper right-hand corner of the table: they have plenty of electrons on their outsides, and this is possible only in atoms near the ends of the periods.

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