Answer: option 4. ns² np⁵
Explanation:
The valence electronic structure of the compounds is the distribution of the valence electrons, i.e. the outermost electrons of the atoms.
The distribution of the electrons in the atomic orbitals is named electron configuration.
Each element has a proper electron configuration which is determined according to a series of rules: lowest orbital energy, Pauli's exclusion principle and Hund's rule.
The valence electronic structure of the atoms is related with the period (column of the periodic table) to which the element belongs.
Each period has a characteristic valence structure (number and location of the outermost electrons). It is this structure what conferes the elements of a same period (column in the periodic table) their similar chemical properties.
This table summarizes the valence eletronic structure of the representative elements:
Period (column) name number of valence eletrons Structure
1 Alkali metals 1 ns¹
2 Alkaline earth metals 2 ns²
13 3 ns² np¹
14 4 ns² np²
15 Pnictogens 5 ns² np³
16 Chalcogens 6 ns² np⁴
17 Halogens 7 ns² np⁵
18 Noble gases 8 ns² np⁶
There you can see that the halogens belong to the period 17, have 7 valence electrons, and their valence electrons are have the structure ns² np⁵.
This is the specific valence electronic structure for the first five halogens:
Halogen atomic number row (n) period valence electronic structure
Fluor 9 2 15 2s² 2p⁵
Chlorine 17 3 15 3s² 3p⁵
Bromine 35 4 15 4s² 4p⁵
Iodine 53 5 15 5s² 5p⁵
Astatine 85 6 15 6s² 6p⁵
There you see the common structre ns² np⁵.
