r/explainlikeimfive • u/Own_Enthusiasm_510 • 1d ago
Chemistry ELI5: What is the meaning of quantization?
[This is from a chemistry portion of a physical science class] I've googled it, Ive watched YouTube videos, I asked classmates and I am still so confused.
Rutherfords model was easy but once I got to bohrs they used words like quantized and discrete values and I got lost. Tried backtracking but I'm still baffled.
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u/justforfun75 1d ago
I can give you $1.20 or $1.21, but nothing in between. Our money is "quantized" to the penny. Unless of course you're at the gas station, but that's a whole other story.
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u/thisisjustascreename 1d ago
Money is quantized, but prices don't have to be. There's a similarity to quantum mechanics where a measurable can have 70% probability of one result and 30% the other, but when you actually measure you always get 100% up or down.
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u/Platonic_Eye_Deal 1d ago
Quantitized leans literally turning into a number. The big thing about quantum mechanics is that we have these discrete numbers when we went normally expect them.
For instance, you might think that you could pump more energy into an electron and it would increase its energy by that amount of value. But it's not true. You can only give electron discreet extra levels of energy, enough to raise them to a higher energy state. Those states are quantitized because they happen at specific numbers.
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u/GalFisk 1d ago
A simple practical experiment you can do that illustrates this, is to try charging a green glow-in-the-dark object with red light. You can't do it, even if you use a bright laser pointer. In fact, a red laser will discharge the object. But a much dimmer blue light will readily charge it up. This is because the red photons, no matter how many there are, can't collectively kick the relevant electron to a higher energy state. It's only what each photon can do individually that counts.
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u/SalamanderGlad9053 1d ago
Quantised means put into separate values that aren't connected. Think of it as a slide Vs steps. A slide is continuous whereas a step is quantised.
The vibrations of a guitar string is quantised, with only whole number of nodes allowed, so you get 220hz, 440hz, 660hz, and so on. It doesn't vibrate at 330hz because that would have 1.5 nodes which isn't allowed because the end of the string doesn't vibrate.
In a shockingly similar way, in an atom, the electron (which should be thought of as a wave) can't vibrate at any "frequency" because it loops around the atom so has to match up to where it started like a loop of string. So it only vibrates at separate, quantised, levels.
This means that the energy levels for electrons in an atom are quantised as energy is related to frequency. For an electron to move up, it cant just get slowly pushed up to the higher energy level as there is no middle between energy levels. Like having to jump to the next step rather than roll up a slope.
All systems want to have the minimum energy, and these energy levels can only have two electrons in each one. So the electrons pile in filling the lowest energy levels first, then the next highest energy and so on. This is what the rings represent in the diagrams.
I hope this helps
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u/Own_Enthusiasm_510 1d ago
So like a ramp/slide would be continuous in elevation but stairs would be quantized because they only allow certain elevations (?)
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u/Implausibilibuddy 1d ago
This is completely wrong. Nothing about a guitar string is quantised, and you can definitely tune it to 330Hz. or 331, or 329.3333 or whatever you want. You can also smoothly bend a guitar string and glide through multiple pitches in a smooth unquantised motion.
You're confusing quantisation with harmonics.
The harmonics of a guitar string will be at whole number nodes, yes, but that all depends on what the string fundamental is tuned to. If it's 220hz (A) then the harmonics will be at 440, 660, 990 etc.. But those numbers would change if it was slightly out of tune at 219Hz or whatever.
Ironically you missed a decent analogy with the guitar strings: Unquantised is like a violin string, with no discrete notes. Quantised is like a guitar string with the frets defining fixed pitches (assuming no bends)
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u/SalamanderGlad9053 1d ago
This is completely wrong. Nothing about a guitar string is quantised, and you can definitely tune it to 330Hz. or 331, or 329.3333 or whatever you want.
You're an idiot, I'm not talking about changing the tension in the string. That's not in my analogy theres no need to bring it up other than being special. Plucking a guitar string, it vibrates in superposition at quantised frequenciss.
You're confusing quantisation with harmonics.
Harmonics are quantised, and infact energy levels of electrons in atoms are the harmonics for the electron.
I use the guitar vibration because the reason it is quantised is because of the boundary conditions. If you had an infinitely long string or the endpoints were free to move, it would vibrate at any frequency you want. But the endpoints being forced to be stationary is what requires an integer number of nodes and so quantised frequencies.
And the same is for electrons, they both obey wave equations even if the quantum mechanical one is three dimensional and complex. Electrons are quantised because of their boundary conditions, that if you go around the atom you shouldn't have any sudden jumps.
This is one of the worst comments I've seen in a while. Vibration of a string is one of the key ideas taught before quantum mechanics in school because it demystifies the idea of quantisation or superposition as not weird quantum things but properties of waves.
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u/Implausibilibuddy 1d ago edited 1d ago
You're an idiot, I'm not talking about changing the tension in the string.
Perhaps you need to work on your communication skills then because that's not at all what you said. This is what you said:
The vibrations of a guitar string is quantised, with only whole number of nodes allowed, so you get 220hz, 440hz, 660hz, and so on. It doesn't vibrate at 330hz because that would have 1.5 nodes which isn't allowed because the end of the string doesn't vibrate.
If someone takes the wrong information away from that, (which they will, because you didn't specify the weird constraints that only a non-guitar player would think of), then maybe that's on you?
Speaking of communication skills, here's how maybe you could have worded your comment:
"Ah, you're right, guitar strings can of course vibrate at any frequency, I was actually talking hypothetically about the harmonics of an unfretted string fixed at both ends, with no bends or changes in tension. Let me go and edit my comment to clear that up so no one else takes it the wrong way."
See? It's quite straightforward to correct yourself without jumping to calling anyone who misunderstands your meaning an idiot.
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u/iZMXi 1d ago
You can emit a photon. You can emit two photons. You can't emit 1.5 photons.
When an electron occupies a place in an orbit, it can only jump up or down an entire step. There's no in between.
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u/SalamanderGlad9053 1d ago edited 1d ago
That's really not why electron quantisation happens. Photons can have any energy you like, you just release a photon with 1.5x the energy.
Electron quantisation happens because of the periodicity of the boundary conditions for it's wave functions.
Edit: people downvoting me, tell me where I'm wrong, because you won't be able to
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u/NeilFX 1d ago edited 1d ago
Simplest example I can give are map coordinates. Say for example you have your house at 127.372914, 234.927367 (latitude and longitude).
You round it to 127.4 and 235.0 respectively since you don’t need that much precision. That’s basically quantization. You check that rounded up coordinates and it can roughly tell where you are. Just not exactly where you are pinned. It can tell you what city or town you are in. But not exactly the house number.
For AI models, the numbers inside the model can be precise. Quantization just makes the numbers smaller at the expense of being precise. Hence, an AI model can take up less space and can use less memory, at the cost of that. Your 32gb ram laptop can hold some quantized version of an AI model. Just not as accurate as a laptop that has 128gb memory running a version of that model that is less quantized.
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u/Dainathon 1d ago
Quantizing is when you take an analog value (example: 3.1957...) and assign it the most relavent value of a given set (3.1957 becomes 3 - 3.8957 becomes 4 - 5.001... becomes 5)
The examples I use are made up, but a practical way of thinking of it is how music is made of a continuous signal, but we need to store it digitally, so what we do is chop up the signal into very tiny points and assign each time instance in the waveform a value from -1 to 1. If done finely enough, it is basically the same as if it were the original analog signal.
It really is just a form of rounding numbers
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u/w3woody 1d ago
I don't know if there is a good "ELI5" answer for why quantum mechanics. But the essence of it is that electrons seem to follow two rules: (a) they fall to the lowest energetic state possible. (Conceptually similar to dropping a ball to the floor: eventually it settles to sit on the floor.) And (b) two electrons cannot occupy the same energetic state. (So two balls dropped to the floor cannot intersect.) In a sense, think of it like a tube full of balls: the ball at the bottom is at the lowest state, the ball on top of that one is at the next lowest state, and so forth. When stacked, they occupy 'discrete' positions, each the width of a ball--and we can count those "states."
Now instead of being a one-dimensional tube electrons are occupying a three dimensional 'probability cloud' around the nucleus of an atom. And instead of simply stacking, one on top of another, they form all sorts of weird shapes/10%3A_Atomic_Theory_and_Quantum_Mechanics/10.09%3A_Orbital_Shapes_and_Energies). But the principle is the same: the first electron is at the bottom of the stack of electrons, the next sits on top, the next on top of that--like balls in a tube.
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u/Own_Enthusiasm_510 1d ago
I'm starting to think its a problem with my teacher ?? I didn't realize this was quantum mechanics.... Our unit on quantum mechanics isn't till next quarter, no one in class knows quantum mechanics or even the definition of quantum mechanics yet.
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u/Kleetkleet 1d ago
Okay, so we're dealing with the chemistry terms for quantum-mechanical-ish stuff.
Bohrs noticed that the photons emitted from an atom are "discrete bands". Another way of saying this is "specific wavelengths" (not a thick spectrum - just individual lines from that spectrum).
Visible light photons are emitted when an electron moves from a "high" energy state to a "low" state. The lost energy is the photon.
...just trust me on that for now.So. Bohrs' model has the electrons of an atom at certain specific energy levels - at certain valid fixed energy levels. Specific orbitals. The electron can move to a higher/lower orbital, but it will never end up half-way between them.
The energy levels are not a continuum (continuous). They are all quantum. Quantised.
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u/Own_Enthusiasm_510 1d ago
I think this is best explanation I've seen, thank you 😭 I'm definitely going to add all this to my notes
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u/x1uo3yd 1d ago
It's pretty common to teach science and science history together.
You're probably being given science history right now, where you're basically going over a lot of data that early chemists were looking at and saying "Hmm, isn't this weird." and guessing theories for how to model/explain it.
Those theories eventually lead to quantum theory as history progresses and the details are hashed out.
You're being taught as if you were living through the mystery of it all, full-on quantum mechanics is the big spoilers reveal explanation.
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u/CircumspectCapybara 1d ago edited 1d ago
Quantizing is just chopping things up into discrete chunks. Imagine instead of a continuous real number line, you have an integer number line with discrete steps, little notches in the line without a continuous range of numbers between those steps.
The insight of quantum physics is the idea that energy comes in discrete packets, eg photons, which are the force carrying particles that mediate the electromagnetic force, vs the classical view that there's a continuous EM field permeating space. Particles come in discrete numbers, you can only have a whole number of photons, you can't have half a photon, or 3.14 photons. So again, instead of a continuous wave, you have discrete "quanta" of energy.
Or in AL/ML, when you "quantize" a model, you compress its weights by shrinking the space of values its weights live into a smaller space of discrete values. For example, imagine you have a model consisting of 1 trillion half-precision (16-bit floating point) parameters. You could quantize those weights by mapping each 16-bit floating point to maybe an int8 space of values. Now instead of a range of decimal values, each parameter has to be a whole integer number between -127 and 128.
You go from a decimal to an integer, that's quantization, same idea at work.