Eli5 why is that an atom is 99,6 % empty space ?
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At the center of an atom you have protons and neutrons. The strong nuclear force holds these particles together, tightly packed, with a distance of about 1 femtometer.
The electromagnetic force gives protons in the nucleus a positive charge. This means the atom attracts a cloud of electrons. Because electrons have little mass, the speed (momentum) they have when they’re close to the nucleus means their position around the nucleus is fuzzy. The most likely places you’ll find the first couple of electrons is roughly around 50,000 femtometers away from the nucleus, depending on the atom.
Two atoms usually interact through their electron clouds, and don’t get any closer than that.
So when people say an atom is almost entirely empty space, they’re trying to talk about the distances that exist between protons and neutrons (1fm) and then between those and their electrons (50,000x). None of these particles have a true size in the sense that we think that a ball has a size, but they do have locations and momentum, which gives us a way of describing a kind of size for them when they’re bound together in something like an atom. It’s just that sometimes it gets fuzzy and we have to talk about averages and probabilities.
Cause atoms are badass. That’s juss how atoms roll. But guess wha, that remaining 0.4% is nothing but empty space too, nothing.
You don’t agree ? Okay, what else are they ? Standard Model stuff ? Fields ? What the heck is a field ? My word, so many fields going every which way and stacked over and over again atop each other ? Fields more like oceans and the Universe exists submerged in multiple types of field oceans at once. yes.
The very same fields that are always there where there is something are also always there where there is nothing. In the reality of the Universe Is and is not are fundamentally the same
if the core (nucleus) of an atom would be the size of an orange, the electron cloud would be the size of Earth. Since we consider the “surface” of the electron cloud the surface of an atom and since nothing is in between, we can say that an atom is mostly empty space.
I think some answers are misleading. Yes quantum uncertainty doesn’t allow to pinpoint the nucleus and electrons as being at a specific point in space.
But the orbitals are not full, they are just density probabilty functions tied to the electrons energy levels. That doesn’t mean the electrons are “distributed” in all that space, it’s just a function that tells you where they are likely to be found if you were to trying to measure them. It’s akin to say that a tennis ball is somewhere in a court. You’re indeed most likely to find in that specific space but the ball itself is much smaller.
When we call it empty it’s because the influence of the electrons is electromagnetic but when considering neutral particle, the part of the atom that can interact, the nucleus, is indeed extremely tiny. (this was observed when looking how neutrons could be deflected/bounced against atoms)
We don’t know the size of the electrons, but we know the actual particles are quite far from the nucleus compared to the size of it (against, because of uncertainty, the actual size/position of the nucleus is not completly known but it’s influence can be measured and detected. That’s where the saying comes from.
What do you mean why? It just is.
Imagine the atom being like the game Pole Tennis(Totem tennis, tether tennis, swingball). The pole being the nucleus and the tennis ball being the electron, only the tennis ball is moving around so fast you can’t see it
You could say the size of the pole tennis game is a sphere around the pole because you don’t know where the tennis ball is (Because its moving so fast)
However, the vast majority of the pole tennis game is empty space, because the tennis ball can only be in 1 place at a time.
If you imagine the solar system as a sphere with the sun at its centre and Pluto’s orbit being the edge, that sphere will be mostly empty space. While planet orbits are mostly in a single plane, you can imagine their orbits being at any angle or location and the result will be the same
Science is mostly apt at answering “how” questions, rather than “why” ones.
Science *observes* and *describes*, finding predictive relations between measurable quantities.
Stuff is the way it is, because it is. Then we give it an explanation that is accurate and useful.
Returning on topic: early atomic physics experiments showed this phenomenon of mass distribution, that can be explained as such:
Electro-magnetic interaction, makes it so electrons have to orbitate at a certain distance from the nucleus, while strong nuclear force makes the nucleus very tightly packed. Electrons are extremely light, whereas atoms are relatively heavy. This implies that most of the mass is in the nucleus.
More sophisticated experiments show a more complex behaviour of matter at very small scales and the simplified description of an atom as a collection of tiny balls becomes inaccurate, even though still effective.
Quantum physics describes particels as “probability waves” and thus you can’t think of an electron (or nucleus) as a tiny ball, but as something “smeared” across a region of space. And you can’t think of empty space as it being really empty anymore.
Also mass at the atomic level is a combination of the “intrinsic” mass of each sub-atomic part and the “additional” mass provided by the strength of their bonding… the game grows ever more complex.
So long story short: our “planetary” description of the atom, implies a significant volumetric void inside an atom. More accurate descriptions drop this idea of such an amout of empty space within the atom for a more complex description.
The atom is made from a nucleus (protons neutrons) and electrons. These are often drawn as small balls. With this interpretation of an atom, you could say there is a lot of empty space between the electrons and the nucleus, but as we looked closer, this was not the case.
The better analogy is that there is a cloud for the nucleus and a cloud for the electron. We know the particles are within their respective clouds, but they don’t have an exact spot where they are.
But even this is wrong the particles aren’t *In* the clouds, the particles *are* the clouds. Location just isn’t well defined.
Look up “atomic orbital shapes” and you can see some of the shapes of these clouds.
Almost all of the mass in an atom is concentrated in the center of the atom in the nucleus, but the nucleus is actually quite small, and is relatively dense. The “”””empty”””” space comes from that being the region where the nucleus interacts with electrons.
I’m simplifying a bit here, but that empty space is being taken up by electrons, and the space where the electrons exist is way larger than the nucleus itself.
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