How does Bromine have seven valence electrons?

This might seem like an extremely stupid question. My calculation is as follows. 2 electrons in first shell, and then 8 in the next four shells. Overall 34 electrons, which leaves one valence electron (not 7?). Anyway, I am trying to do an electron-dot formula on NBR3, and it doesn't work because it can't make sense that BR has only one valence electon. Please explain?