Question Video: Identifying Which Element Has an Atomic Radius Larger Than Aluminum Chemistry

Which of the following elements has an atomic radius larger than that of aluminum? [A] Cl [B] Na [C] S [D] Si

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Video Transcript

Which of the following elements has an atomic radius larger than that of aluminum? (A) Chlorine, (B) sodium, (C) sulfur, or (D) silicon.

This question is asking us to compare the atomic radii of different elements. The atomic radius of an element is the distance from its nucleus to its outermost electrons. Scientists can measure the atomic radius by taking half the distance between the two nuclei of adjacent atoms bonded together. To answer this question, we need to take a look at the periodic table, specifically at period three, which contains all five of the elements mentioned in the question.

In order to answer this question, we need to know how atomic radius changes across a period. Once we know this trend, we can find which of the answer choices has the largest atomic radius. Let’s compare aluminum and silicon to visualize this change. Since we don’t know what size they are yet, we’ll start by drawing them as the same size. The first difference we can notice is that when we move to the right in a period, the number of protons increases. Silicon has one more proton than aluminum. With more protons in the nucleus, there’s a stronger positive charge there and thus a stronger inward pull on the electrons. As a result, there’s also a smaller atomic radius.

So, the trend is clear. If more protons means a smaller atomic radius, then the atomic radius decreases to the right and increases to the left. If we wanna find the element with an atomic radius larger than that of aluminum, we want to find the element to the left of aluminum on the periodic table. In this case, that’s sodium. Sodium has fewer electrons than aluminum and therefore a weaker inward pull on its electrons, which results in a bigger atomic radius. Which of the following elements has an atomic radius larger than that of aluminum? That’s answer (B) sodium.