For an element with atomic number 35, which one of the following will be the correct number of electrons in its valence shell based on Bohr’s model of an atom?

For an element with atomic number 35 (Bromine), the electronic configuration is determined by distributing 35 electrons into shells. According to Bohr's model and the Aufbau principle, the configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵ [1]. In terms of shell-wise distribution (K, L, M, N), this corresponds to 2, 8, 18, 7 [1]. The valence shell is the outermost shell, which for Bromine is the fourth shell (n=4). This shell contains the 4s and 4p subshells, holding 2 and 5 electrons respectively, totaling 7 valence electrons. This is consistent with its position in Group 17 of the periodic table, where elements like fluorine and chlorine also possess 7 valence electrons [1]. Therefore, the correct number of electrons in its valence shell is 7.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.3 HOW DO METALS AND NON-METALS REA ALS REACT? > p. 47