Question

The valency of an atom can be found from its electronic configuration of its atom.Write the electronic configuration of ${}_{19}{}^{39}\mathrm{K}$ and hence its valency as well as the formula of its chlorides and oxides.

Answer 1

• It is given that the atomic number of potassium (K) is 19.
• In an electrically neutral atom, the number of electrons and number of protons will be the same. Thus K will have 19 electrons.
• Thus the electronic configuration: - 2,8,8,1.
• In the valence shell of potassium there is only one electron. Hence its valency is 1.
• On losing one valence electron, potassium will be changed to potassium ion (${\mathrm{K}}^{+}$) with octet configuration.
  
• Oxygen has atomic number 8 and hence it has 8 electrons. Thus the electronic configuration:2,6.
• The number of valence electrons in potassium is 1 and that of an oxygen atom is 6.
• Oxygen needs 2 electrons to attain octet (${\mathrm{O}}^{2-}$).In presence of an oxygen atom, the potassium atom will lose one electron.
• Hence oxygen will accept one electron from each potassium atom.
• Therefore one oxygen and two potassium atoms are needed to form potassium oxide with formula ${\mathrm{K}}_2\mathrm{O}$.
  
• The chlorine atom has atomic number 17, hence it has 17 electrons. The electronic configuration:2,8,7.
• Chlorine atom needs one more electron to attain octet.
• Hence potassium atom will give up one electron and the chlorine atom will accept that.
• Therefore, each potassium atom needs only one chlorine atom to form potassium chloride. Hence the formula is $\mathrm{KCl}$.