Despite the similarities in the chemical reactivity of elements in the lanthanide series, their abundances in Earth's crust vary by two orders of magnitude. This graph shows the relative abundance as a function of atomic number. Which of the following statements best explains the sawtooth variation across the series? (a) The elements with an odd atomic number lie above the belt of stability. (b) The elements with an odd atomic number lie below the belt of stability. (c) The elements with an even atomic number have a magic number of protons. (d) Pairs of protons have a special stability.

Video transcript

Welcome back everyone. We're told that even though the elements in the land tonight series have a comparable chemical reactivity. Their abundances in the crust of earth differ by two orders of magnitude. The graph below displays the relationship between relative abundance and atomic number, which Damon explains why elements with even atomic numbers have more abundant isotopes. So looking at our graph given, we can see that at the three highest points we have our element Siri um with the atomic number being 58. So we see that that has an even atomic number of 58. Our second highest point, which is Neodymium has an atomic number of 60. Also another even number. And then our second or sorry, third highest point for element die pros me um Has an atomic number of 66 which is also an even number. So based on our based on our prompt, we do see that our graph affirms the evidence that elements with even atomic numbers are definitely the most abundance in or have a common abundance here. So, going to our statements below, we have each statement which either discusses pairs of protons and neutrons. In statement, be a magic number of protons. And statements see a magic number of neutrons or in statement D. A reference to the band of stability. So what we want to think of is we're going to recall that as a number of protons increases our column force strength also will increase recall that our column force is for proton proton interactions. So this is the definition of our column force, proton proton interactions. And if the column force is increasing in strength, this tends to, we'll say which tends to break the nucleus apart, recall that in our nucleus of our atoms are where our protons and neutrons are contained. And so if the nucleus is at risk of being broken apart, we would say thus more neutrons are needed to keep the nucleus stable. And sorry, let's make sure this is all visible. So thus more neutrons are needed to keep the nucleus stable. And we would say because only neutrons experience attractive nuclear force, so the ability to be able to bring this nucleus together by this attractive force. And so there is a certain point to where the repulsive Kalume forces between our protons Will not be able to be compensated by the addition of these neutrons. And this point is only occurring at the point where our atomic numbers hit a value of 83 and above. So recall that at atomic number and up, elements with Over 83 protons. Because we recall that our atomic number Z tells us our number of protons, so, elements with more than 83 protons do not have stable nuclei. So based on what we've outlined, going back to our answer choices, we can agree that ruling out statements B and C definitely makes sense. It's not about having a magic number of protons or a magic number of neutrons statement D. We can rule out because we know it's not about the band of stability here. It's particularly statement A, which says that elements with even atomic numbers have more abundant isotopes because of their special stability associated with pairs of neutrons, pairs of protons and neutrons. So statement A is going to be the best statement given to explain why we have such a high abundance of elements with even atomic numbers. I hope everything I reviewed was clear. If you have any questions, please leave them down below and I will see everyone in the next practice video.