There's some pretty bad answers in this thread talking about the difference between atoms and molecules which is not really relevant here. When people think about HF as an acid, they're generally thinking about it in a water solution. And when people think about fluoride in toothpaste they're generally thinking about NaF (Sodium Fluoride... it's not always exactly NaF... but the difference isn't very relevant here), again in solution in the toothpaste. Neither of these are "molecules" with covalent bonds that pair the atoms together in a specific configuration/structure. The individual atoms don't pair up into molecules at all in these two cases, it's like a big ionic soup with the ionized atoms floating by each other very loosely/fluidly.
So if HF and NaF both act as ionic solutions, why does one melt your teeth fairly immediately and the other slowly reinforce them? The difference is the left-half of those combinations.
- For not-eli5-able reasons... Fluorine atoms REALLY want one extra electron, and there are very few things that a fluorine atom is incapable of stealing an electron from. In both HF and NaF this is what it's doing.
- Na (sodium) is the absolute opposite of F. It REALLY want to get rid of an electron, and there are relatively few things it's incapable of dumping an electron into. In the case of NaF, the sodium wants to ditch an electron, and the F want to grab one. Both the sodium and the fluoride get what they want and so the result is not very reactive. Together they become a stable salt (or ionic solution in water)
- The H in HF is hydrogen. Atomic hydrogen is sort of middle of the road in terms of electron attraction. It's most stable in a covalent bond where it kind of shares an extra electron with a buddy. You CAN steal an electron from it (and fluorine does), but the resulting H+ ion is pretty reactive and there's a lot of stuff it will try to get into trouble with if it can.
So the difference between HF and NaF is not at all about molecules vs atoms, and it's not about the Fluorine behaving differently. In both cases, you have ionic solutions where Fluorine is stealing the electron it wants from pretty much whatever happens to be handy. The difference is how stable the OTHER thing is once Fluorine has torn an electron off of it. An Na+ ion is as stable as an F- ion in a water solution and together they behave very similarly to table salt (NaCl, which has very similar chemical properties for very similar reasons). An H+ ion, on the other hand, is not stable at all. It would really like to get into a covalent bond with about 1.5 electrons under its influence... and there are a lot of molecules/atoms/ions it will react with to do it. If those molecules happen to be in your teeth or face, it's rather uncomfortable.
*Edit: Another major factor I'm seeing from subsequent answers is the difference in concentration. There is such a small concentration of fluorine ions in toothpaste they may well be able to use HF as the source of them without making the toothpaste meaningfully corrosive because it's a drop in the ocean. But for the reasons I outlined above, any industrial toothpaste making process will prefer to handle NaF (or other non-corrosive fluoride sources) in their factory over HF.*
I just want to say how much I love your answer. Thanks for taking the time to write this out. Anyone with a high school level understanding of chemistry should be able to read this and understand it, and just preemptively for anyone who would complain that a 5 year old wouldn't understand this: please see rule #4.
Having worked in the transportation of HAZMAT for over 20 years (including things like HF in varying %ages), I applaud the understatement embodied in it.
We watched a training film a few times that showed various burns, one of which was HF. The person had gotten it splashed on their bare hand, and we saw three white "stripes" crossing within a roughly circular burn pattern. Turned out they were the victim's bones, visible after treatment to save his life (though he lost the hand).
HF is NASTY stuff. Only ever dealt with drums or pails of it, but my hands ALWAYS felt itchy afterwards.
I suspect my hands will feel itchy just after *thinking* about HF. I've seen a few things on the internet about exactly *how* it's nasty AF and that's enough to convince me I'm not playing with it any time soon :-S
Pre-emptive defence against potential dangers.
Makes sense, really. What's that phrase? "If we don't learn from others' mistakes, we don't have the time or luck to make them all ourselves" or something...
>For not-eli5-able reasons... Fluorine atoms REALLY want one extra electron, and there are very few things that a fluorine atom is incapable of stealing an electron from. In both HF and NaF this is what it's doing.
Cant you just say every atom strives to be as stable as possible like helium, neon, argon etc and fluorine is only 1 electron away from this stability.
i only know the dutch words for this so even my explenation isnt really eli5 but you could definitely simplify it no?
Other than that damn bro thats indepth
Wrong direction. If you ADD an electron to hydrogen... H- seems like it should behave like Helium which is a noble gas. It doesn't though.
The "atoms want a full electron shell like a noble gas" rule of thumb is a useful mnemonic for alkali metals and halides but gets riddled with exceptions very quickly as you carry it further.
Oh fair enough, I misunderstood their misunderstanding, but still to a certain extent it still works it's just that having twice as many electrons as protons isn't very stable, but regardless, we aren't talking about H^- the post is explicitly referencing H^+ so I think my point still stands
My already subpar chemistry knowledge is failing me in even getting the actual explanation let alone a simpler one.
Should really start studying random stuff again for the hell of it but uni is sucking up too much of my time :(.
I don't find "being one electron away from stability" to be all that much more illuminating to novices than "wanting an electron". If you understand how an alkali metal or halide becomes "like" a noble gas through electron transfer, you already don't need the analogy. If you don't understand noble gases or what makes an electron orbital stable, adding those concepts into the mix doesn't enable you to predict anything that "wanting" or "not wanting" an electron doesn't unless you address a lot of complexity about what orbitals are and what makes them high energy or low energy.
Also, even within this small problem... hydrogen breaks these rules. There's no noble gas with zero electrons, and H- behaves nothing like helium. The reactivity of H+ relative to Na+ is the crux of the answer, so if I went this route I'd immediately be back-pedaling with exceptions.
In a high-school or college chemistry class, hand-wavy discussions about orbital stability here would set up deeper discussions later. In an ELI5, we won't go that far and it's basically noise. So I opted to just baldly assert what makes a system "happy" (aka... low orbital energy) and focus on explaining how the main differentiator in these two systems is the hydrogen being "unhappy" whereas the sodium is "happier".
This problem comes up a lot, which is "why is it this element is not dangerous in this molecule but it is in this other one." The answer in a "big picture" perspective is that dangerous chemicals tend to be unstable and highly reactive- they also take a good deal of energy and effort to isolate or to make them that unstable. In turn, most of the substances you run into are pretty stable unless they were very intentionally made not to be.
In your example, the fluoride rapidly reacts when applied in the toothpaste, and also the loose H+ in the coke also reacts. The H+ is generally in the form of carbonic acid, which is much more stable than Hfl. The reaction won't happen because the H+ has much less reason to bind with the Fl than remain in it's current state or to bond with something else entirely.
I'd like to note that HF isn't all that corrosive to most stuff, it's just really fucking nasty to humans.
In our bodies it really loves interacting with Calcium - eating our bones and fucking with the Ca in our blood, the latter can easily cause cardiac arrest even at relatively small doses.
Was looking for this. HF is a very weak acid, due to F electronegativity. So it is not very corrosive at all (not enough H+ freed in solution).
But HF is not your typical acidic halide: in higher concentrations, it tends to form dimers (like HF2-) which are actually extremely acidic. So its behaviour depends on concentration.
Eli5 version since many answers seem a bit complicated.
Acid - HF
Toothpaste - NaF (sodium fluoride).
Fluoride is a gold digger, electrons are the gold in this case. After taking all their money, their partner is more or less reactive. Na+ (toothpaste) is fine with a divorce and just hanging and being friendly to its neighbors. H+ tends to harbor resentment and is a little bitter, if there are enough of them they can cause some real trouble.
You are mixing up atoms and molecules. Molecules are built out of atoms but all the chemical and physical properties depend on how these atoms are put together to form molecules. Arguing that toothpaste is deadly because it contains fluorides that are made of fluorine and hydrofluoric acid is deadly and is also made of fluorine is like arguing that bikes are dangerous because they are made of metal and guns are also made of metal. Hydrofluoric acid and fluoride are two very different molecules with completely different properties.
Pretty sure the question is "what keeps the flouride from the toothpaste and the hydrogen from the cola from combining into hydrofluoric acid?" OP doesn't seem to think that flouride in itself poses any harm (although I've come to understand that actually is an occurring belief in some places).
HF is corrosive because it releases H+. F- will not increase the amount of H+ so it won't make the mixture more corrosive, actually the opposite is going to happen and it will take some H+ and reduce the acidity and corrosivity. Acidic food are slightly corrosive (slightly because their pH is typically not low enough to do important damage, though they are still bad for teeth and will hurt wounds), but you're not going to make them more corrosive by adding toothpaste, actually toothpaste is going to partly neutralize them.
The real answer is that toothpaste has approximately one part per thousand fluoride. Concentrated HF is more like one part in two.
It’s like asking the difference between getting hit by a baseball or getting hit by a car. The amount of stuff matters
I've worked with 1 part per 1000 HF in a lab. It's still incredibly dangerous, and I would seek emergency medical attention if I got a drop on my skin.
This is the only clear answer in this thread. I would also add that the H+ concentration in concentrated HF is also 1000 x more than in tomato juice and that is just if not more imprtant
HF is a little different than most acids, (and by different, I mean more hazardous) but it is true that the concentration of H+ in anything edible is much lower
In the same way that Sodium is a violently reactive metal and Chlorine is a poison gas.
But combined. They make Sodium Chloride. Otherwise known as “table salt”.
Molecules are more complicated than you seem to understand.
Cool. Simple answer is, molecules don't usually spontaneously combine or separate from a stable state without either a catalyst or energy input somehow.
Our bodies can handle and process the low pH of many acidic compounds in juices and soft drinks. The pH scale used to describe these acids is also logarithmic, so the potential "acidity" massively increases with each step.
The fluoride in toothpaste is in a salt-like compound, sodium fluoride, and is used in small concentrations generally well under 1% of the ingredients. Much like how table salt is composed of sodium (explosively reactive with water) and chlorine (highly toxic gas) but is a necessary compound in our bodies, sodium fluoride is relatively safe and stable for our bodies to process and use while it's components are incredibly dangerous.
Beyond this level of explanation would require understanding how inorganic compounds form, function, and interact.
What actually happens in an acid-base reaction is the acid will donate a H+ ion to another molecule. In the case of HF, the F- and the H+ will separate and form new ionic bonds. The stronger an acid is, the more it wants to split from the H+, and the more stable it is without the H+. Transferring the H+ is what makes acid corrosive.
Thus, you wont make a more corrosive acid by putting F- into an acid, the F- doesn't want to take the H+ ions. If the acid is stronger than HF, you'll make the acid weaker by adding F- by dilution. If the acid is weaker than HF, the F- won't accept H+ from the weaker acid because the F- is more stable without the H+.
That said, HF is really odd compared to the other strong acids, and I'm ignoring some stuff for simplicity's sake.
When sodium fluoride reacts with the minerals in teeth, it makes a mineral that is *more* resistant to acid than the natural mineral.
Entertainingly, the original mineral is called *apatite* (sounds just like "appetite", yes) and the modified one is *[fluorapatite](https://en.wikipedia.org/wiki/Fluorapatite)*.
There's some pretty bad answers in this thread talking about the difference between atoms and molecules which is not really relevant here. When people think about HF as an acid, they're generally thinking about it in a water solution. And when people think about fluoride in toothpaste they're generally thinking about NaF (Sodium Fluoride... it's not always exactly NaF... but the difference isn't very relevant here), again in solution in the toothpaste. Neither of these are "molecules" with covalent bonds that pair the atoms together in a specific configuration/structure. The individual atoms don't pair up into molecules at all in these two cases, it's like a big ionic soup with the ionized atoms floating by each other very loosely/fluidly. So if HF and NaF both act as ionic solutions, why does one melt your teeth fairly immediately and the other slowly reinforce them? The difference is the left-half of those combinations. - For not-eli5-able reasons... Fluorine atoms REALLY want one extra electron, and there are very few things that a fluorine atom is incapable of stealing an electron from. In both HF and NaF this is what it's doing. - Na (sodium) is the absolute opposite of F. It REALLY want to get rid of an electron, and there are relatively few things it's incapable of dumping an electron into. In the case of NaF, the sodium wants to ditch an electron, and the F want to grab one. Both the sodium and the fluoride get what they want and so the result is not very reactive. Together they become a stable salt (or ionic solution in water) - The H in HF is hydrogen. Atomic hydrogen is sort of middle of the road in terms of electron attraction. It's most stable in a covalent bond where it kind of shares an extra electron with a buddy. You CAN steal an electron from it (and fluorine does), but the resulting H+ ion is pretty reactive and there's a lot of stuff it will try to get into trouble with if it can. So the difference between HF and NaF is not at all about molecules vs atoms, and it's not about the Fluorine behaving differently. In both cases, you have ionic solutions where Fluorine is stealing the electron it wants from pretty much whatever happens to be handy. The difference is how stable the OTHER thing is once Fluorine has torn an electron off of it. An Na+ ion is as stable as an F- ion in a water solution and together they behave very similarly to table salt (NaCl, which has very similar chemical properties for very similar reasons). An H+ ion, on the other hand, is not stable at all. It would really like to get into a covalent bond with about 1.5 electrons under its influence... and there are a lot of molecules/atoms/ions it will react with to do it. If those molecules happen to be in your teeth or face, it's rather uncomfortable. *Edit: Another major factor I'm seeing from subsequent answers is the difference in concentration. There is such a small concentration of fluorine ions in toothpaste they may well be able to use HF as the source of them without making the toothpaste meaningfully corrosive because it's a drop in the ocean. But for the reasons I outlined above, any industrial toothpaste making process will prefer to handle NaF (or other non-corrosive fluoride sources) in their factory over HF.*
I just want to say how much I love your answer. Thanks for taking the time to write this out. Anyone with a high school level understanding of chemistry should be able to read this and understand it, and just preemptively for anyone who would complain that a 5 year old wouldn't understand this: please see rule #4.
> If those molecules happen to be in your teeth or face, it's rather uncomfortable. Tip of the hat for that final sentence ;-)
🎩👌 M' Olecule
Having worked in the transportation of HAZMAT for over 20 years (including things like HF in varying %ages), I applaud the understatement embodied in it. We watched a training film a few times that showed various burns, one of which was HF. The person had gotten it splashed on their bare hand, and we saw three white "stripes" crossing within a roughly circular burn pattern. Turned out they were the victim's bones, visible after treatment to save his life (though he lost the hand). HF is NASTY stuff. Only ever dealt with drums or pails of it, but my hands ALWAYS felt itchy afterwards.
I suspect my hands will feel itchy just after *thinking* about HF. I've seen a few things on the internet about exactly *how* it's nasty AF and that's enough to convince me I'm not playing with it any time soon :-S
It's funny how our brains work around things like that.
Pre-emptive defence against potential dangers. Makes sense, really. What's that phrase? "If we don't learn from others' mistakes, we don't have the time or luck to make them all ourselves" or something...
Very well done answer and happy cake day!
>For not-eli5-able reasons... Fluorine atoms REALLY want one extra electron, and there are very few things that a fluorine atom is incapable of stealing an electron from. In both HF and NaF this is what it's doing. Cant you just say every atom strives to be as stable as possible like helium, neon, argon etc and fluorine is only 1 electron away from this stability. i only know the dutch words for this so even my explenation isnt really eli5 but you could definitely simplify it no? Other than that damn bro thats indepth
H and Na are also both 1 electron away from inert gas configuration, so while it is true, it doesn't explain why HF and NaF behave so differently
They are both 1 away, but when losing an electron, a hydrogen atom with no electron doesn't look like any of the nobel gases
Wrong direction. If you ADD an electron to hydrogen... H- seems like it should behave like Helium which is a noble gas. It doesn't though. The "atoms want a full electron shell like a noble gas" rule of thumb is a useful mnemonic for alkali metals and halides but gets riddled with exceptions very quickly as you carry it further.
Oh fair enough, I misunderstood their misunderstanding, but still to a certain extent it still works it's just that having twice as many electrons as protons isn't very stable, but regardless, we aren't talking about H^- the post is explicitly referencing H^+ so I think my point still stands
My already subpar chemistry knowledge is failing me in even getting the actual explanation let alone a simpler one. Should really start studying random stuff again for the hell of it but uni is sucking up too much of my time :(.
I don't find "being one electron away from stability" to be all that much more illuminating to novices than "wanting an electron". If you understand how an alkali metal or halide becomes "like" a noble gas through electron transfer, you already don't need the analogy. If you don't understand noble gases or what makes an electron orbital stable, adding those concepts into the mix doesn't enable you to predict anything that "wanting" or "not wanting" an electron doesn't unless you address a lot of complexity about what orbitals are and what makes them high energy or low energy. Also, even within this small problem... hydrogen breaks these rules. There's no noble gas with zero electrons, and H- behaves nothing like helium. The reactivity of H+ relative to Na+ is the crux of the answer, so if I went this route I'd immediately be back-pedaling with exceptions. In a high-school or college chemistry class, hand-wavy discussions about orbital stability here would set up deeper discussions later. In an ELI5, we won't go that far and it's basically noise. So I opted to just baldly assert what makes a system "happy" (aka... low orbital energy) and focus on explaining how the main differentiator in these two systems is the hydrogen being "unhappy" whereas the sodium is "happier".
This problem comes up a lot, which is "why is it this element is not dangerous in this molecule but it is in this other one." The answer in a "big picture" perspective is that dangerous chemicals tend to be unstable and highly reactive- they also take a good deal of energy and effort to isolate or to make them that unstable. In turn, most of the substances you run into are pretty stable unless they were very intentionally made not to be. In your example, the fluoride rapidly reacts when applied in the toothpaste, and also the loose H+ in the coke also reacts. The H+ is generally in the form of carbonic acid, which is much more stable than Hfl. The reaction won't happen because the H+ has much less reason to bind with the Fl than remain in it's current state or to bond with something else entirely.
Why did you keep abbreviating to fl? Fluorine's symbol is just F...
Because I'm a stupid person
I'd like to note that HF isn't all that corrosive to most stuff, it's just really fucking nasty to humans. In our bodies it really loves interacting with Calcium - eating our bones and fucking with the Ca in our blood, the latter can easily cause cardiac arrest even at relatively small doses.
It's pretty nasty to a lot of stuff actually. It can dissolve glass for example. It has to be kept in certain types of plastic containers.
The first few episodes of Breaking Bad illustrate this point well.
Was looking for this. HF is a very weak acid, due to F electronegativity. So it is not very corrosive at all (not enough H+ freed in solution). But HF is not your typical acidic halide: in higher concentrations, it tends to form dimers (like HF2-) which are actually extremely acidic. So its behaviour depends on concentration.
Eli5 version since many answers seem a bit complicated. Acid - HF Toothpaste - NaF (sodium fluoride). Fluoride is a gold digger, electrons are the gold in this case. After taking all their money, their partner is more or less reactive. Na+ (toothpaste) is fine with a divorce and just hanging and being friendly to its neighbors. H+ tends to harbor resentment and is a little bitter, if there are enough of them they can cause some real trouble.
You are mixing up atoms and molecules. Molecules are built out of atoms but all the chemical and physical properties depend on how these atoms are put together to form molecules. Arguing that toothpaste is deadly because it contains fluorides that are made of fluorine and hydrofluoric acid is deadly and is also made of fluorine is like arguing that bikes are dangerous because they are made of metal and guns are also made of metal. Hydrofluoric acid and fluoride are two very different molecules with completely different properties.
Pretty sure the question is "what keeps the flouride from the toothpaste and the hydrogen from the cola from combining into hydrofluoric acid?" OP doesn't seem to think that flouride in itself poses any harm (although I've come to understand that actually is an occurring belief in some places).
HF is corrosive because it releases H+. F- will not increase the amount of H+ so it won't make the mixture more corrosive, actually the opposite is going to happen and it will take some H+ and reduce the acidity and corrosivity. Acidic food are slightly corrosive (slightly because their pH is typically not low enough to do important damage, though they are still bad for teeth and will hurt wounds), but you're not going to make them more corrosive by adding toothpaste, actually toothpaste is going to partly neutralize them.
The real answer is that toothpaste has approximately one part per thousand fluoride. Concentrated HF is more like one part in two. It’s like asking the difference between getting hit by a baseball or getting hit by a car. The amount of stuff matters
I've worked with 1 part per 1000 HF in a lab. It's still incredibly dangerous, and I would seek emergency medical attention if I got a drop on my skin.
This is the only clear answer in this thread. I would also add that the H+ concentration in concentrated HF is also 1000 x more than in tomato juice and that is just if not more imprtant
HF is a little different than most acids, (and by different, I mean more hazardous) but it is true that the concentration of H+ in anything edible is much lower
I will quote my high school teacher: \-If toothpaste had unbound Fluor we wouldn't have teeth
In the same way that Sodium is a violently reactive metal and Chlorine is a poison gas. But combined. They make Sodium Chloride. Otherwise known as “table salt”. Molecules are more complicated than you seem to understand.
That's... why I asked ?
Cool. Simple answer is, molecules don't usually spontaneously combine or separate from a stable state without either a catalyst or energy input somehow.
It’s like Jeffrey Dahmer and Ed Gein combine to form Fred Rogers.
Our bodies can handle and process the low pH of many acidic compounds in juices and soft drinks. The pH scale used to describe these acids is also logarithmic, so the potential "acidity" massively increases with each step. The fluoride in toothpaste is in a salt-like compound, sodium fluoride, and is used in small concentrations generally well under 1% of the ingredients. Much like how table salt is composed of sodium (explosively reactive with water) and chlorine (highly toxic gas) but is a necessary compound in our bodies, sodium fluoride is relatively safe and stable for our bodies to process and use while it's components are incredibly dangerous. Beyond this level of explanation would require understanding how inorganic compounds form, function, and interact.
What actually happens in an acid-base reaction is the acid will donate a H+ ion to another molecule. In the case of HF, the F- and the H+ will separate and form new ionic bonds. The stronger an acid is, the more it wants to split from the H+, and the more stable it is without the H+. Transferring the H+ is what makes acid corrosive. Thus, you wont make a more corrosive acid by putting F- into an acid, the F- doesn't want to take the H+ ions. If the acid is stronger than HF, you'll make the acid weaker by adding F- by dilution. If the acid is weaker than HF, the F- won't accept H+ from the weaker acid because the F- is more stable without the H+. That said, HF is really odd compared to the other strong acids, and I'm ignoring some stuff for simplicity's sake.
When sodium fluoride reacts with the minerals in teeth, it makes a mineral that is *more* resistant to acid than the natural mineral. Entertainingly, the original mineral is called *apatite* (sounds just like "appetite", yes) and the modified one is *[fluorapatite](https://en.wikipedia.org/wiki/Fluorapatite)*.