Why is that Br has more electron affinity than F? 

Dear Student,

The high electron affinities of the halogens are a result of their small size, high effective nuclear charge and having an almost complete outer shell of electrons. The addition of an electron to an atom results in a completely filled shell or make them to have stable configuration. The size of F is smaller than bromine. So,the negative charge electrons are highly concentrated in small area and repels the incoming electron thereby reducing the force of attraction of the nucleus towards the adding electron and hence decreasing the electron affinity. On the other hand bromine has the larger size as compared to F therefore electronic repulsion would be less . Thus, bromine has a highest value of electron affinity.  

Regards

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