For Group 13–17 elements in the third row of the periodic table
and beyond, the octet rule is often not obeyed. A friend
of yours says this is because these heavier elements are more
likely to make double or triple bonds. Another friend of
yours says that this is because the heavier elements are larger
and can make bonds to more than four atoms at a time.
Which friend is more correct?

Question

Accepted Answer

Welcome back everyone. We're told that the octet rule is often disobeyed by elements in the third row and beyond of the periodic table. And which of the below statement explains this statement reads at a heavier element attracts more electrons. We want to recall electron affinity which is the energy of attracted electrons to an atom. And if we think of our trend on our product on our periodic tables, we would recall that electron affinity increases as we go from the left to the top right of our periodic table. So it's increasing as a trend on the periodic table. Now, when it comes to heavier elements or heavier atoms, we recall that are larger atoms with more mass go further down on our periodic table. So we get to larger atoms as we go down our periodic tables. And so that would not correspond to having a increase in electron affinity. That would actually be a decrease in electron affinity since we have heavier atoms. And that is because that is opposite to our trend of increasing electron affinity, which increases as you go up the periodic table. So we would say that statement A is ruled out as a false choice because it does not explain our octet rule. So moving onto choice B, it says that a heavier element is more likely to form double or triple bonds. And we want to recall that not all heavy elements will favor forming double or triple bonds. So this is going to be false because it's just simply not always true. So we can roll choice be out. And lastly we have choice C, which reads a heavier element can make bonds to more than four atoms. And we can recall that elements in period three and below have larger atomic radius and therefore more space and available orbital's to accommodate more electrons. And we should recall that these sorts of elements also will experience less destabilization from additional electron electron repulsion. And we can recall our trend on our periodic table of atomic radius, which is increasing as we go towards the bottom left of our periodic table. So this is with regards to atomic radius. And this trend was in regards to electron affinity. So if we have more space and more available orbital's to accommodate more electrons, it would make sense that heavier elements can make bonds to more than four atoms. And that is why we can say that choice C. Is true, and that would be the explanation for why the octet rule is often disobeyed by period three elements and below. So C is our final answer. I hope everything I reviewed was clear. If you have any questions, leave them down below and I'll see everyone in the next practice video

Verified Solution

Key Concepts

Octet Rule

Bonding in Heavier Elements

Coordination Number