Question

How will you find the valency of chlorine, sulphur and magnesium?

Answer 1

Write down the electronic configuration of the 3 elements mentioned in the question. Valency is used to determine the number of electrons gained or lost by the atom in order to attain stable octet configuration. Remember to fill electrons in increasing order of energies of orbitals as stated in Aufbau principle.

Complete step by step answer:
As we know, the atomic number of chlorine is 17. There are 17 electrons, so its electron configuration is 2, 8, 7 in K, L, M shells respectively. It has 7 electrons in its valence shell (M shell). Thus chlorine atoms can accept 1 more electron to achieve the inert gas electron arrangement (of 8 valence electrons). So its valency is 1. The atomic number of sulphur is 16. There are 16 electrons. So its electron configuration is 2, 8, 6 in K, L, M shells respectively. It has 6 electrons in its valence shell (M shell). A sulphur atom can accept 2 more electrons to achieve the inert gas electron arrangement. So its valency is 2. The atomic number of magnesium is 12. It has electron configuration of 2, 8, 2. A magnesium atom has 2 electrons in its outermost shell (M shell). It can lose its 2 outermost electrons to achieve the inert gas electron configuration. So its valency is 2.

Therefore, the valency of chlorine, sulphur and magnesium is 1, 2 and 2 respectively.

Note: We will generally see 2 cases. The outermost shell of an atom contains less than or equal to 4 electrons. Then its valency is equal to the number of electrons in the outermost shell. The second case is where the outermost shell contains more than 4 electrons, and then its valency is equal to 8 - no. of valence electrons in the atom.