Answer to Question #141136 in Physical Chemistry for Francis

Question

Copper chloride (CuCl2) is a stable compound, whereas neither CaCl nor CaCl3 are known as unstable compounds. Account for this observation.

Answer 1

Electron configuration of Ca is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

So, Ca has a tendency to lose two of its valence 4s electrons to attain the electronic configuration of Ar which is an innert gas and thus, has most stable electron configuration.

So Ca forms Ca²⁺ ion. In CaCl, Ca is +1 oxidation state and thus, always has a tendency to lose one more elecron to gain the innert gas electronic configuration. So CaCl if formed anyway , may quickly transform into CaCl₂.

Now, in CaCl₃, Ca is in +3 oxidation state which is rather uncommon for Ca since Ca can lose two electrons maximum to attain the innert gas confguration. Also, with lose of electrons the nuclear attraction force to the remaining electrons increases in Ca²⁺ ion which also prevents further electron loss from th filled 3p subshell.