hydroxypcp

hydroxypcp t1_jc9tx6k wrote

(orgchemist not physics one here) that sounds about right. If you start adding atoms, going 2, 3 etc there is no clear number when it suddenly behaves like a macroscopic solid. As with everything in science, "solid" is just a concept/model and there is no one 100% clear way to define when a set of particles switches from non-solid to solid

my thought process is: if we add Pb atoms and they stick together, then at what number do we consider it a solid particle? You wouldn't count alkane vapour where the molecules consist of dozens of atoms a solid (or liquid), right? In essence they are chemically bonded and stay together, so why would 20 or 30 Pb atoms together be considered differently? So what is it, 100, 200? It is pretty arbitrary

and it's not like if it's, say, 200 then at 199 it's not a solid and at 200 suddenly it is and behaves totally differently

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hydroxypcp t1_jc9tak2 wrote

I disagree. For one, a single lead atom is basically a radical so there is no energy barrier to overcome on its side for the reaction to occur (since it has no metallic bond to other Pb atoms). This means the likelihood of a reaction with all other collision parameters being the same is increased by orders of magnitude

Second, things move hella fast at room temp and the mean free path length at STP is very small. This means that it will have collided with air molecules a whole lot before it reaches any surface. I don't remember the numbers off the top of my head for some shoddy napkin math but I'm very confident that if we account for both these factors, Pb will have reacted with oxygen with a very high likelihood before touching a surface unless it formed like, right next to it.

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