The bromine atom (Br) has an atomic number of 35, which means it has 35 electrons. To determine the valence electron configuration of bromine, we need to look at the electron configuration of the previous noble gas, which is argon (Ar). The electron configuration of argon is 1s² 2s² 2p⁶ 3s² 3p⁶.
Bromine is located in the fourth period (row) of the periodic table, so its electron configuration builds upon the electron configuration of argon. The remaining electrons in bromine are distributed as follows:
4s² 3d¹⁰ 4p⁵
The valence electrons of an atom are defined as the electrons in the outermost energy level (shell). In the case of bromine, the outermost energy level is the fourth energy level (shell), which consists of the 4s and 4p orbitals. Therefore, the valence electron configuration of bromine is 4s² 4p⁵.
In summary, the valence electron configuration of a bromine atom is 4s² 4p⁵.