What is the molecular formula for 20Ca and 17Cl?

Answer 1

Ca and Cl are elements and dont have a formula as such.

But if your asking what compound they'll form.....

calcium is in group 2, meaning is has 2 electrons on its outter shell and a configuration of [Ar] 4S2, and chlorine is in group 7 so there are 7 out of 8 electrons in the outtermost shell.

So chlorine wants to gain an electron have a full shell and calcium has two to give before it gets down to a stable configuration of [Ar], therefore it will take two chlorine atoms to remove these two electrons, so the compound formed will be CaCl2.

Its also worth noting that this is a neutral compound also, since calcium lost 2 electrons it has a charge of +2 and each chlorine gains an electron so it has a charge of -1 and there are two of them so altogether that gives -2. This also suggests that the compound is an ionic compound.

The name of this compound is calcium dichloride, but usually its just called calcium chloride and its used in dessicators to keep samples in a dry environment.

Answer 2

CaCl2 with Calcium being the cation and Chlorine being the anion