Which of the following is the valence elec- tronic structure for a halogen? 1. n s1 2. n s2 3. n s2 n d10 4. n s2 n p5 5. n s2 n p6

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.