The structure will be tetrahedral. The hybridization for tetrahedral ions and molecules is sp3. The Bromate ion will have 32 valence electrons. Br has 7 valence electrons, 4 O atoms will have 6 valence electrons, and the negative charge of -1 will add 1 electron.
7 + 24 + 1 = 32 electrons.
The structure is the same as that of the ClO4^- ion. If you have Java installed on your browser you should be able to see the 3-D structure of the BrO4^- ion.
Hope this is helpful to you. JIL HIR