How do properties of halogens differ from noble gases?
Halogens are very reactive and noble gases are very nonreactive.
Halogens are very reactive because they have seven valence electrons and need one more to have eight valence electrons (an octet). They react with metals and other halogens to get an octet. When this happens, the atoms become stable and have noble gas configurations.
The noble gases have filled valence shells as they occur in nature. Helium has a duet of valence electrons, and the rest of the noble gases have an octet. Because of this, they are very nonreactive.