Eli5 why is that an atom is 99,6 % empty space ?
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Also this leads rapidly to a question of what is empty and what is mass really. And then we firmly outside of eli5 area 😀
It’s like if you look at the earth and moon as one system, and called that an “atom”. Most of that system would be empty space, since there’s a lot of emptiness between the earth and moon.
An atom is similar, where the electrons “orbit” around the nucleus. Between the electrons and nucleus, is a lot of empty space, where that figure comes from.
One way to think about atoms is like tiny repelling magnets with a magnetic field much larger than the actual magnet. So when another magnet gets close these to push eachother to maintain their distance. Only by exerting a great force on them (like in a neutron star or a black hole) will these two tiny magnets actually make contact.
This is the electromagnetic force field around the atoms core and its much much larger than the core. Atoms are somewhere around 99.9999% empty due to this.
That is commonly said and is sort of true but not really.
Of one were to imagine electrons like little balls zipping around, then the atom would be kind of like the solar system in terms of “stuff vs. empty space”. One big mass in the centre, a few minor masses around and a whole load of nothing in between.
But that picture isn’t correct in that electrons are NOT balls zipping around. They do not exist in one specific point at a specific time(until they interact with something). They “fill” specific areas around the nucleus according to the specific orbitals’ shapes (and we know what those shapes are).
In other words, that space isn’t really empty, it’s full of the electrons’ quantumly dispersed presence.
It’s empty because it’s empty, is the short version. The reason why they can seem so substantial despite being mostly empty is that much of the interaction that atoms have with each other is through the electromagnetic force.
When two objects bump into each other, it’s not the mass of the atoms colliding, it’s the electrons in those atoms repelling each other via their electric fields.
An atom isn‘t 99.6% empty space. That‘s what scientists thought in the 1910s, but since the 1920s we know that electrons in atoms don‘t behave like tiny balls (like we thought before) but more like clouds. You wouldn‘t call a cloud an empty space. This means the space of an atom is 100% occupied by the electrons.
Electrons repel each other, because they have a similar charge. This means they don’t get too close to the nucleus, because they would put them too close to each other. Atoms don’t get much closer to other atoms because the electrons clouds don’t want to touch.
The 1920s theory of matter was that electrons and nuclei are discrete things finite in size. You can reasonably test this theory by shooting a stream of smaller atoms at a thin film of bigger ones, and what you get is a scatter pattern consistent with most passing through, some being deflected back etc. This was alpha radiation at a gold sheet (alpha rays are helium atoms without electrons).
This essentially invalidated theory that atoms were one solid mass of protons and electrons together.
That 1920s understanding starts to come apart the more you ask questions like how big is a nucleus or an electron, and where is it, and what is it made of.
If the model of an electron orbiting a nucleus was correct you should be able to do experiments where you could see an electron on different sides of the atom for example.
Turns out, matter is much more complicated than that. Electrons, when bound to nuclei are much more like a charge distribution than a discrete blob orbiting a centre. Many electrons create a cloud of distribution.
Nuclei have the same issue, protons and neutrons are made of quarks exchanging gluons to stick together, meaning they have some internal structure as well, and the size of a nucleus is really the area with charge and forces in it.
So generally when we say atoms are mostly internally empty, we mean the nucleus is a small blob and electrons are small blobs orbiting it.
But electrons and nuclei (and protons and neutrons) are themselves not really finite discrete blobs.
They’re not, atoms are packed full of stuff. They are just less dense in some some spots and really dense in others.
Because it is. This is what the world looks like. Atoms were not designed, so there’s no “purpose” to their structure. When people describe them, they describe the structure and the forces involved, but just like there’s no answer to “why is there something and not nothing?” there’s no answer to “why” in this case. “Empty space” is a simplification- outside of the nucleus, the space itself is packed with *probabilities*….
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