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you are right. it will instantly react with oxygen radicals which are freely available from photo dissociation of O3 and NO2.

In some sense they do. Ionic chemicals are just things that are attracted together and can pack together to make a solid. They aren't "bonded" like covalent chemicals, they are just attracted. We write NaCl, but really every sodium is just attracted to the six nearest chloride ions. The same principle applies to a statically charged balloon.

But with static electricity the charges involved are much smaller and the particles are bigger. In salt you have single atoms with missing (or extra) electrons. In static electricity the particles are huge (10^17 or so atoms of it's dust) and the charge is much smaller: like hundreds or millions of elections meaning the charge to mass ratio is 10^10 less. (these numbers are of the top of my head, but the principle is correct)

So lower charge + higher mass = weaker bond.

They also aren't consistently sized, so you can't get the consistent packing of particles like in a salt.

The first sentence was discussing a scenario where we only have the lead atoms (at their extremely low density) and nothing else. I added the remaining gases back in the second sentence.

Not necessarily milliseconds. It can take minutes for an atom of gad in STP atmosphere to bumble its way to a room's wall.

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Every element and compound can be, it's just that for most solids the partial pressure is so low as to be negligible.

Well, all you’re saying is right. But it’s also pretty unlikely to really find a single Pb atom flying around. There’d be a gradient originating from the source, with most heavy Pb atoms actually chilling at the source and not wanting to really move (think elastic impact) as all the other atoms/molecules colliding with it have way less mass. Only the most energetic ones escape (we’re overlooking any kinds of wind here for simplicity, just focusing on the thermal energy). So Pb will most likely see other Pb and form more inert clusters before even noticing any other molecules flying around. Those clusters will get oxidised on the surface eventually, but definitely not instantly or „quickly“ (however uncertain that term might be).

Now, in a realistic scenario, with wind working it’s magic and mixing everything, you’re probably right to disagree. That’s why my answer was „yes and no“. Realistically, it’d probably get oxidised at some point. Even a radical reacting with another radical needs to (Pb and O2/O•) fulfil certain strict geometrical conditions in order to pair the lone electrons. Those conditions can only be achieved randomly and under a certain energy threshold, which is why radicals in gas phase can be (but definitely don’t have to) pretty stable. I aimed to explain the reasons why this isn’t really a straightforward case.

Again. So basically, it’s pretty unlikely that a single Pb gets quickly oxidised. It will happen to some atoms though. It’s way more likely for Pb to form bigger clusters, which are more probable to hit (or rather be hit by) oxygen to react on their surface.

Edit: I’m all for napkin math though. I’ll try to remember to do it later.

Here's a good resource on the subject, from the lab of Casey Dunn, a siphonophore researcher.

Your argument is solid; in functional terms, the zooids in a colonial organism can be considered organs in an integrated body. The reason why we call these organisms "colonial" is actually a bit abstract: it has to do with the evolutionary/developmental history of these organisms.

You know the concept of homology? Like how your hand is homologous to a dolphin flipper, or the wing of a bat? All three organs can trace their history back to an original forelimb in the shared mammalian ancestor of all three animals. This is the key to understanding the definition of zooids, too. Each zooid in a colonial organism is homologous to the entire body of an individual in related, non-colonial organisms. For example, the reproductive zooid of a Portuguese man o' war is homologous to the entire body of a jellyfish.

It's a bit as if an offshoot population of humans evolved into grotesque creatures made up of hundreds of little human bodies, linked together, performing different tasks. Functionally, each of those little bodies can be viewed as just an organ — but looking at it from a perspective of homology, you've got a colonial organisms made out of human-shaped zooids.

(And, as noted in the linked text, all animals can be viewed as colonial in this sense, because each of our cells is homologous to the entire body of one of our single-celled ancestors.)

Gas, liquid, solid — it’s mostly about how close molecules/atoms are to each other (if you abstract enough from interatom interactions). Gaseous state means that everything is so far away and moves so quickly in random, it doesn’t feel any kind of interaction from outside. For it to happen you either need to reduce the distance (increase pressure) or to take away some energy from particles (cool down), so they could “talk” to each other. It’s called condensation and unless it happens to radon, you can easily think of atoms of lead separated from it as single atoms, it’s unlikely that they will condense together by themselves which will allow you to think of it as liquid/solid. Otherwise, you can think of it as a really expanded gas diffused into radon. Depends on what you’re trying to achieve and which processes to describe.

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With lead alone almost all atoms would hit the wall and freeze out in milliseconds, although theoretically the vapor pressure is not zero. With other gases you can have lead in there for a while outside of equilibrium.

?? are you saying lead can be a (very low partial pressure) gas at STP?

Pretty much my line of thinking, yeah.

(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

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.

It's fine to view space as expanding, since again, that represents a convenient coordinate choice. I use it frequently in calculations. The key point is just that this "expanding space" doesn't have physical consequences.

It's like how two people walking due north from the south pole will gradually separate from each other despite walking in the same cardinal direction, but the process of walking north doesn't induce an expansion force on your body.

Sure it would. Imagine that a bunch of particles all explode outward from a point at different speeds. The ones moving fastest will end up farthest, and you automatically end up with a picture where recession speed is proportional to distance.

As far as I'm aware, "arbitrarily many"

If this one introductory thermodynamics course I did last semester is any indication

> For example, if “space was expanding” except for things that are close enough overpower it with gravity, how would that result be different from dark energy creating a repulsive force except for things that are close enough to overpower it with gravity?

The main problem is that dark energy's repulsion has no intrinsic link to the global expansion of the universe. For example, as I noted in another comment, in Einstein's static universe (in which matter's attraction balances dark energy's repulsion), there is a repulsive force even though the universe is not expanding.

More generally, the repulsion from dark energy has no link to the cosmic expansion rate at a given instant. It does connect to the rate of change of the cosmic expansion rate (i.e. the acceleration), but this link is only partial, since dark energy is only one of the factors controlling the rate of cosmic acceleration (the other main one being matter, which decelerates expansion).

> Also, how can galaxies be “carried by their initial momentum” as you confirmed above AND all be moving away from one another at the same time. Maybe I’m misunderstanding something but that doesn’t really make sense. The only way all galaxies that are not locally bound to one another could be moving away from one another is if that space between them is somehow expanding, similar to the “dots on the surface of a balloon” metaphor that is often used. If we instead imagine an “initial momentum” scenario, it suggests a single point of origin in space, similar to an explosion. But in the case of an explosion, there is a center source, which the universe doesn’t appear to have.

The universe can originate from a single point in spacetime while still having no center in space. Due to the principle of relativity, any observer departing from that point has an equally good reference frame, so there is no way to decide that one observer is better than another.

(You could still suggest defining the center in terms of "distance from the edge". There doesn't have to be an edge, though.)

> Also, the red-shifting caused by an explosion would not be so uniform, but have many items moving away at much faster speeds than others relative to the observer.

That's not a fundamental limitation, it's just intuition from the explosions you know. The initial "explosion" doesn't have to be messy (for example if it arose from inflation). Also note that in an expanding system, velocities self-sort because if an object is moving rapidly with respect to the material near it, it's not going to stay near that material. Instead it will gradually end up near material moving at the same speed. (This effect is essentially the cosmological redshift applied to massive particles.)

So how many atoms do you need to be able talk about states of matter?

> How far radon will go via diffusion until it decays in h.l. 3.8 days?

Many meters (as rms). Random air currents are the dominant effect unless you have an extremely calm room.

The scale height for nitrogen and oxygen is ~8 km, something with 7 times the mass still has ~1 km, so in perfect equilibrium you would expect the concentration to change by ~0.2% over the height of a room. In practice you never achieve such a perfect equilibrium unless you completely seal the room, keep its temperature completely constant and wait for a very long time.

So 7x mass nearly doesn't matter.

How far radon will go via diffusion until it decays in h.l. 3.8 days? Its products are to be bound faster, I suppose.