Answer to Question #145264 in Organic Chemistry for Maloth VAMSHI KRISHNA

Question

Why ca form only cacl2 and not form cacl

Answer 1

There is an "octet rule", which states that main-group elements tend to bond in such a way that they have 8 electrons in the outermost shell (in other words, they obtain the noble gas configuration). Ca has two valence electrons, so, in order to obey the octet rule, it has to lose these two electrons. The electron configuration of Ca atom is [Ar]4s². So the only way for it to obtain the noble gas configuration [Ar] is to lose these two 4s-electrons. Chlorine, in its turn, has 7 valence electrons, hence only one electron should be gained to complete the octet. That is why 2 chlorine atoms are needed to take 2 electrons from one atom of calcium, and the stable compound has formula CaCl₂.