Consider the Mg²⁺, Cl^-, K⁺, and Se^2- ions. The four spheres below represent these four ions, scaled according to ionic size. (b) In terms of size, between which of the spheres would you find the (i) Ca²⁺ and (ii) S^2- ions?

Video transcript

Hello everyone today. We are being given the following problem and asked to solve for it. This is the relative ionic sizes of beryllium two plus sodium plus fluoride minus and sulfide to minus or shown below. And in between which ions which you place magnesium two plus and oxygen two minus ions. So the first thing we want to do is relate the relationship between electrons and size. In a general principle that we can apply is that the more electrons we have, we're going to have a bigger size. Alright, so with that logic cat ions or positively charged ions will typically be smaller than our neutral atoms and ions or negatively charged species will typically be larger as they contain more electrons in there orbital's. And so now we can compare the charges with the ions that we have in the question with our ions pictured here. So with our magnesium two plus, we're going to go ahead and place that right between beryllium two plus and sodium plus and so why between those two? Well, another periodic trend is that size increases as we go. So if we're looking at a periodic table, the size of the irons are going to increase as we go to the left and downward of the periodic table. And so we note that magnesium is just below beryllium and therefore will be smaller than beryllium. And so oxygen two minus will of course go between our fluoride and our sulfide right here and because it is larger than fluoride but smaller than sulfur to minus. It would be placed right there. And so this is going to be our final answer. I hope this helped until next time.