Conductors in the triboelectric series

[KV789]

I teach electricity in grade 9. For the concept of conductors, they are described in the textbook as atoms where the outer electrons can easily move from one atom to another (e.g. copper). But I noticed that on the triboelectric series, copper and other metals are listed as having a strong(er) hold on electrons when charged by friction with something like wool or glass (which are considered electric insulators). I guess my question is how do I explain why copper becomes negative when rubbed with insulators like wool/silk/glass if copper also has a weaker hold on its outer electrons as a conductor?

Any insight would be appreciated! Thanks!

 

[Baluncore]

Welcome to PF.
That is a really good question, and I also want to know the answer.

Maybe electrons are being wiped from the insulator because they prefer the more positive copper where the surface has been swept clear of some electrons, inducing a local positive charge at the point of contact.

 

[DaveE]

I think this is all about the "wool/silk/glass" and how much it wants to grab an extra electron. Metals can easily give up their conduction band electrons to a receptor. If so, it will then be harder to remove additional electrons from the metal because of the charge imbalance.