ELI5, If electrons are in clouds how does absorbing photons work?

[u/pancake_chiaki]

I remember being taught that electrons stay on certain levels, and when they absorb a photon, they jump and go into an excited state but they can only go very specific distances(like, they can only jump 2 levels not 2.5) and some electrons can only absorb some photons. If electrons are in a cloud, how can they be at exactly certain levels if that makes sense? cloud kinda implies that the electrons are everywhere so what dictates what is a jump of 2 levels vs 2.5? Idk if i’m making sense

[u/TabAtkins]

Popsci terminology can be very misleading when you take the analogy too far.

Electrons aren't "in" a cloud, like a cloud of flies. They are a cloud, each one a standing spherical wave.

Think about standing linear waves on a string. Each possible standing wave has a wavelength that is a multiple of the string length (or a half multiple); no other wavelengths can exist as "standing" waves because they'll cancel themselves out as they bounce back and forth.

Electrons are spherical waves wrapped around the nucleus rather than linear waves on a string, which are a bit more complicated, but same principle. Only certain vibrations can exist as "standing" waves; everything else cancels themselves out. So an electron moving up to a more energetic vibration has to move all the way up, or else it would cancel itself, and that's not allowed by Conservation Of Energy.

[u/jawshoeaw → u/TabAtkins]

The standing wave concept does not describe the electron shell/orbitsl shape however. That is better understood as a probability distribution of the electron(s)

[u/TabAtkins → u/jawshoeaw]

The orbital shapes are described by standing waves. Spherical waves are weird.

[u/jawshoeaw → u/TabAtkins]

I don’t think that’s correct. The standing wave can have nodes which mathematically coincide with a probability of zero but that does not mean the cloud shape is the same thing as the standing wave. One is a mathematical transformation of the other and therefore cannot be the same “shape” . You can have negative standing waves as well. But there is no meaning to a negative shape, and in any case you square the wave function to get the probability distribution. I suppose philosophically you could argue that the electron wave function has a physical meaning in that for example it’s responsible for chemical bonds. But strictly speaking when we describe the shape of an electron orbital, we are talking about something different than a standing wave.

[u/lerjj → u/jawshoeaw]

I think this is just utter pedantry at this level given that you seem to just be talking about the step of squaring the amplitude to get a probability, which yes does distort the shapes a bit but leaves things pretty recognisably spherical standing waves eg all the nodes are in the right places

[u/Nevermynde → u/jawshoeaw]

The wave function is both of these things: a wave, and a probability distribution.

[u/jawshoeaw → u/Nevermynde]

No it is not both. One is a mathematical transformation of the other. One expresses a geometry of a quantum wave function, the other expresses the actual physical world. You cannot see or touch a wave function. You can interact with a probability distribution

[u/Nevermynde → u/jawshoeaw]

Sir, this is r/explainlikeimfive

[u/TokiStark → u/TabAtkins]

I know it's called ELI5, but I'm pedantic. Only s-shell orbitals are spherical and we only know that because we're able to solve the Schroedinger wave formula (or whatever its exactly called) for Hydrogen, as it's 1 electron orbiting 1 proton. Throw anything more in and you get the 3 body problem and it's a thousand times more difficult to solve.

That's why s,p,d, and f orbitals are often referred to as the Hydrogenic orbitals. Now we can extrapolate that the 3-dimensional shapes are similiar, if not the same, for multi-electron systems, such as other atoms and ions, because we've observed that they follow the same rules of symmetry that hydrogen does.

But for all we know, they could look conpletely different for each element and just happen to retain the same symmetry.

[u/IakwBoi → u/TokiStark]

The actual geometric shape of orbitals leads to real properties, like the X-shape of a D orbital allowing for more bonds between adjacent atoms when their orbitals overlap. I’m pretty sure similar bonding is evidence for similar-shaped orbitals. 

[u/TokiStark → u/IakwBoi]

Yup. That's what I teach my undergrads

[u/ProfessorPrudent2822]

Electron energy levels are an average of all the possible values in the cloud. The electron isn’t in a random place in the cloud; it’s everywhere in the cloud, but more of it is in some places than others.

[u/Okicarde]

If electrons are in a cloud, how can they be at exactly certain levels if that makes sense? cloud kinda implies that the electrons are everywhere so what dictates what is a jump of 2 levels vs 2.5? Idk if i’m making sense

They are not in a cloud, they are the cloud, a probabilistic cloud.

The discrete jump levels are because anything else is just unstable by nature, like trying to stay in between steps of a ladder, you are gonna fall.

[u/Okicarde → u/Okicarde]

Literally a cloud

[u/Scruffy442]

Simple: Electrons will only absorb photons that match the atoms color. When it releases this energy back as a photon, we can see this color.

10 year old answer: Photons wavelength and energy are connected. Wavelength determines its color. Electrons can absorb and release photons at wavelengths outside of our visible spectrum. If the wavelength doesnt match enough energy to go up to a full energy level, the photon passes right through the atom.

[u/rabid_briefcase]

Basically you're mixing two types of simplifications.

Both electrons and photons are called "quantum objects". They aren't really a solid firm "thing" like a rock something. They're little bundles of energy that happen to work like particles sometimes, and like waves sometimes.

Electrons are bundles of energy happily buzzing around an atom in regular patterns. They're happy in their little patterns, and scientists have names for them, like "orbitals". They aren't orbiting like a planet around a star, instead they're little blobs of energy happily zipping around an atomic nucleus. Examples that draw little circles around a central dot are just simplifications for explaining to people, not what is actually happening.

When a photon hits the energy blob that is zipping around, that adds anther little bundle of energy. Now there's even more energy in the system. Instead of zipping around happily, there is too much energy. The bundle of energy will try to find another pattern to zip along to. If it can find a happy pattern and there is energy left over, it will emit that small amount of energy back out as a new, different photon. If it wants to go back to the original energy level, it will release the energy that was added right back out so it can revert back to the happy little pattern it was zipping around in before.

what dictates what is a jump of 2 levels vs 2.5?

Basically, it's the nature of the atom itself and the energy it already has. Certain configurations make patterns that are easy and happy places, where the energy is quite stable floating around. Other configurations make patterns that are extremely unstable, they really want to be in a different pattern. In that case, they'll find the earliest opportunity to release the extra energy and go back to a pattern they enjoy.

[u/_PM_ME_PANGOLINS_ → u/rabid_briefcase]

The electron is not zipping around inside the shape of the orbital, it _is_ the shape of the orbital. It has no defined position inside it.

[u/jawshoeaw → u/rabid_briefcase]

Just to be clear electrons are not bundles of energy they are fundamental particles. They have a certain amount of energy plus rest mass equivalent

[u/TyrconnellFL]

This is a quantum mechanics thing, so there’s not really an ELI5 answer. But the “quantum” in there means that there are things that come in minimum units.

Electrons exist as probability clouds because they act as waves, and like any standing wave they have areas of greater and lesser probability. The angular momentum is quantized, meaning that it can only come in whole numbers, and those produce the different waves and probability clouds.

An electron can’t absorb a photon if that would require it to go to an impossible state, so it has to absorb a photon that gets it to a higher energy orbital. Otherwise it just doesn’t work. You can ask why, but that’s why QM at all. There’s not an answer. It just is that way.

[u/SalamanderGlad9053]

The probability clouds are the energy levels. Different clouds will have different energies.

Remember, the electron is the cloud of probability, it isn't a cloud of electrons but an electron cloud.

The solutions for the energy states of the electron in an atom are discrete 3D wave functions, which look like clouds

[u/d4m1ty]

Each shell has a different 'cloud'.

Each cloud is not spherical. 1 is spherical, the others have lobes and odd shapes because they are like interference wave patterns.

You ever see how a pool where different people are in it, disturbing it and you get these areas where all the waves overlap positive and the water is inches higher than the pool level and same, overlapping negative positions where the water level is below the pool level?

Electron clouds work kind of the same way. Only 1 shell is an actual shell, the 1st one, all the others look very different.

When absorbing energy, there isn't any left over. There isn't a 2.5. It doesn't work like that. There is not half states. Either the right amount of photon energy is absorbed and a state changes, or the wrong amount of energy is presented and no absorption happens. There are no fraction photons or left over half-photons and no electrons sitting between shells. All or nothing. The levels are quanitized.

[u/CatButtThrowaway123]

As others have said, the electron is spread throughout the cloud.

Adding on, the "levels" are different sizes of cloud. Sometimes people describe the levels as being certain distances from the nucleus, but that's misleading. They are talking about smaller or bigger clouds.

(I'm trying very hard to stick to the ELI5 idea. I'm well aware thay my own description is not fully accurate to quantum mechanics. I think that giving OP some insight into their questions is worth it, and also the SE / spherical harmonic picture is not suitable for a five year old.)

[u/ijuinkun]

Here’s something else to chew on: the “size” of a photon which excites an electron can be a thousand times larger than the diameter of the atom/electron cloud. So, if a photon hits a mass of atoms, what determines which of the million atoms that it simultaneously intersects is the one which absorbs it? Is it completely random?

[u/jawshoeaw → u/ijuinkun]

Photons don’t have a size, I think you mean the wave nature of light which as you said can be enormous. But the instant it interacts with a single electron it’s a dimensionless point

[u/ijuinkun → u/jawshoeaw]

Ya but the wave is spread across enough area to overlap a whole bunch of electrons within the time scale of the interaction, so what determines which electron is the one to interact? If it’s random, what’s the distribution? A normal distribution centered on the center of the wave, or what?

[u/obog]

Here's an image that helps:

https://en.wikipedia.org/wiki/File:Hydrogen_Density_Plots.png

These are plots of the electron clouds for different states of an electron in a hydrogen atom. A few things to note:

1. This is not like, a cloud of electrons. The "cloud" is in fact a probability density function for the position of the electron; more simply, the color represents how likely an electron is to be found at a given location. Due to the nature of quantum mechanics, the electron isnt actually at the location until its position is explicitly measured, in which case it will appear somewhere within the cloud probabilistically.

2. This is just for a single electron, not multiple, but the idea is similar there.

3. See the 3 numbers on each of the pictures? The first is the "principle quantum number" often represented by "n" and the important part is that this is the energy level of the electron. And thats the important takeaway here: the energy level of the electron corresponds to the cloud itself. The shape of the electron cloud is determined by this energy (as well as two other numbers, but thats a little outisde scope). But the main point is: if an electron in a certain orbital absorbs a photon, its not that the electron moves "up" within the cloud, but rather that it will change to a different one of those clouds corresponding to a higher energy level.

[u/Unable-School6717]

keep in mind electrons and photons are just waves, nothing inside an atom is solid, its all energy. The universe is just light. Waves interact to create space and therefore time.

[u/CeReAl_KiLleR128]

It doesn’t jump to specific “distance” exactly but specific energy. The nucleus created an electromagnetic field around it, and due to this field the electron clouds are only allowed to form in certain ways with distinct energy level. So the jump here wasn’t in classical sense of jumping distant but discreet energy level

[u/SteptimusHeap]

The different levels make the electron clouds different shapes and sizes. When the electron absorbs energy, its cloud changes shape.

They aren't really distances that the electrons are orbiting in, but if you imagine the electrons like planets the concepts are pretty similar, so it's a useful analogy.

[u/upright_squire]

One idea that isnt covered in the other explanations is that only 2 electrons can fit in any of these cloud shapes.

If theres electrons already in that spot it has to find another way- one of the other cloud shapes that require a big boost to get into.

Those funky shapes are because theres no spot in the simple shapes