Describe the structures of the white and red allotropes of phosphorus, and explain why white phosphorus is so reactive.

Video transcript

Alright. Hi, everyone. So this question says that the two most common allotropes of phosphorus are white and red phosphorus identify which allotrope is more reactive and explain your answer. Now recall that the term allotrope refers to different physical forms of a given element. So for example, graphite, charcoal and diamond, all of those are different physical forms of carbon. And we can differentiate between white and red phosphorus by considering their structure. Now recall first and foremost, right, that red phosphorus is characterized as being a polymer, right? It has a polymeric structure in which phosphorus atoms are held together by covalent bonds. So because it's a polymer, right? It creates these relatively large structures in repeating units, right? So be because of this, the structure itself is considered more stable because the polymeric structure allows or less bond strength, right? The phosphorus atoms are better spaced apart which causes less strain between them. But the same cannot be said for white phosphorus, white phosphorus has a molecular formula of P four and it's classified or characterized as being a tetrahedron in shape, right. So it creates a kind of pyramid that is overall non polar. Now, ideally because there are four atoms of phosphorus connecting together, we should expect to see oops 90 degree angles in our structure. However, in the actual structure of white phosphorus, the the real bond angles are actually 60 degrees, which is remarkably small considering what we would expect to see from a structure like P four right now, because this angle is so much smaller than expected. This creates an an unusual amount of ring strain because these phosphorus atoms are in are in relatively close proximity that creates a strain between them. Now recall that ring strain compromises the stability of a given structure, right. So because there is so much ring strain, the bonds between phosphorus atoms are going to be considered weaker, which makes the structure overall less stable and by consequence more reactive, right. So the reason why white phosphorus is so much more reactive than red phosphorus is because of the ring strain in its structure compromising the overall stability, right. So just to reiterate white phosphorus is more reactive because of the bond strain or ring strain for that matter in the unusual structure of the molecule. And there you have it white phosphorus is more reactive because of the bond strain in the unusual structure of the molecule. So with that being said, thank you so very much for watching. And I hope you found this helpful