Calcium and Chlorine Formula?

Question

Hello! I have a big problem on this question and I can't figure it out, this is the only question I have throughout my whole assignment.

Here's the question:

Calcium (20Ca) and chlorine (17Cl) can combine to form the salt calcium chloride. Based on the number of electrons in their valence shells and their bonding capacities, what would the molecular formula for this salt be? a. __________

Which atom becomes the cation? b. ________

Thanks in advance. :D

Answer 1

Calcium has 2 valence electrons while Chlorine only has 1. It takes 2 atoms of chlorine to interact with one atom of calcium to give it an overall neutral charge. Therefore the chemical formula would be CaCl2

As an ion, Calcium has a charge of +2 and Chlorine has a charge of -1. You can look at it this way:

A chlorine atom has 7 valence electrons wants one more electron (negative charge) to be happy (happy meaning having a full valence shell).

By picking up that one extra electron (which has a negative charge) gives it a negative charge

On the other hand Calcium has 2 valence electrons. It would like to loose 2 electrons or pick up 6 in order to have a full valence shell. It is much easier for it to loose 2 than to pick up 6 so that is what it does. By loosing 2 electrons it looses 2 negative charges which make it more positive than it normally is.

So, as an ion Calcium has an ionic charge of +2 and chlorine has an ionic charge of -1 (which is why it needs 2 chlorine atoms for one calcium to give it an over all neutral charge [+2 + -1 + -1 = 0] CaCl2)

Anion is a negatively charged ion

Cation is a positively charged ion

the anion in this example is chlorine; having an ionic charge of -1

the cation in this example is calcium; having an ionic charge of +2

Answer 2

a. CaCl2

b. Calcium