Many early chemists noted a diagonal relationship among ele-ments in the periodic table, whereby a given element is some-times more similar to the element below and to the right than it is to the element directly below. Lithium is more similar to magnesium than to sodium, for example, and boron is more similar to silicon than to aluminum. Use your knowledge about the periodic trends of such properties as atomic radii and Zeff to explain the existence of diagonal relationships.

Video transcript

Welcome back everyone. Early chemists observed that a given element is usually similar to the element diagonally downwards and to the right of it than the element directly below it. For example, aluminum and uranium both have an atomic radius of 125 PK meters. Despite their locations in the periodic table. Apply your knowledge of effective nuclear charge to explain this relationship. Our first step is to think of our periodic table and we want to recall our trends first for effective nuclear charge, which we should recall is going to increase as we go towards the top right of our periodic table. And we want a second recall our trend for atomic radius, which on our periodic table is going to increase towards the bottom left of our periodic table. Now, with these trends in mind, let's also make note of the location of aluminum and germanium on the periodic table. When we find aluminum on the periodic table, we'll find it in group three A across Period three of our periodic table. So it's going to be around here on our periodic table. If we assume that this location is around where Group three is period three. Now, thinking of where germanium is, G, We'll find Germanium in group four a. On the periodic table across period four. So because we recall that our period number on the periodic table corresponds to N. Which we recall represents our energy level of our atoms. And we see that germanium is on period four, we would say that germanium lies at a higher energy level being an equals for so with that higher energy level, we would expect a increased radius of germanium compared to aluminum, which also would honor our trend of increasing atomic radius downwards and towards the left of our periodic table, which we do see that germanium is more underneath aluminum based on its position on the periodic table. However, according to the pump, they will have similar radius is and this is going to be explained by the fact that based on our other trend that we noted down which is effective nuclear charge, germanium being more towards the right of our periodic table than aluminum is going to have a higher effective nuclear charge. So let's write that down, Germanium will have a higher effective nuclear charge based on its position In Group four A. Whereas as we stated, aluminum is located in group three A. So because of this higher effective nuclear charge, we can imagine our atom of germanium and Its electron cloud which should have around four energy levels. So each of these circles, I'm drawing around germanium will represent its energy levels. And we want to recall that because we have a high effective nuclear charge with germanium, we're going to have therefore a greater attraction of electrons to germanium nucleus. So all of our electrons present are going to be more greater attracted towards the center where our nucleus lies for germanium. And therefore we can say that our electron cloud is pulled closer to the nucleus. Sorry. So this is nucleus here, which causes germanium to have a smaller atomic radius. So that expected increase in atomic radius based on our trend for germanium would actually be offset by this electron cloud being pulled closer to the nucleus due to that high effective nuclear charge that germanium has based on our periodic trend. So we'll write that statement out as our final answer to say that the increase in radius by the additional energy level of germanium is offset by a decrease because of its greater effective nuclear charge. And this results in aluminum and germanium having similar. And this statement is going to be our final answer to complete this example, which will correspond to choice C in the multiple choice. I hope everything I reviewed was clear. If you have any questions, please leave them down below and I'll see everyone in the next practice video.