Why is H²O harmless, but H²O²(hydrogen peroxide) very lethal? How does the addition of a single oxygen atom bring such a huge change?
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Because a single oxygen atom is very dangerous in and of itself. Oxygen is very reactive and it *hates* being alone. Whenever it is by itself, it looks for the nearest thing it can attach to and attaches to it.
The oxygen in water is very cozy. It has two Hydrogen buddies that give it all the attention it wants and it has no desire to go anywhere else.
The oxygen in peroxide is different. This is a case of *three’s company, four’s a crowd.* The hydrogen-oxygen bonds here are quite weaker. Two Hydrogen can keep the attention of a single Oxygen just fine, but they can’t keep the attention of two very well. The relationship is unstable and the slightest disturbance – shaking, light, looking at it wrong – causes one of those Oxygen to get bored and look for a better situation. If that situation happens to be inside your body then that can do bad things. The atoms of your body don’t particularly like being ripped apart by oxygen atoms. Well, the atoms don’t care, but the tissue, organs, and systems that are made of atoms don’t like it.
EDIT:
As u/
breckenridgeback pointed out, it is more so the oxygen-oxygen bond that is the weak link here (the structure of H2O2 is, roughly: H-O-O-H). This would leave H-O and O-H when it broke apart but this itself isn’t stable. If H2O2 is left to decompose by itself one of those H’s will swap over to form H2O and the free O will combine with another free O to form O2.
A single atom is a pretty big addition in chemistry.
An extra atom is what changes sodium metal(that violently explodes in water) into table salt.
Oxygen is pretty reactive. A lot of things form with it like oxides(things rust), oxidation, etc.
Water is the stable version of hydrogen and oxygen. It doesn’t readily decompose into other things.
Cramming an extra oxygen into it makes it not really want to exist. It’s looking to offload that oxygen. Which is why it decomposes pretty easily to water and oxygen.
When it decomposes is the kicker. The extra oxygen “steals” electrons from cell walls, causing the cell to die.
[pretty much this meme. ](https://images.app.goo.gl/7CmoSM4hE9z9fQG7A)
Red dress- any thing else.
Guy- oxygen molecule.
Girlfriend- Hydrogen Peroxide.
A single atom can, on its own, be very reactive. This is very true for oxygen atoms. Add that to an otherwise inert molecule, and you have a sort of carrier for the reactive atom.
Ok the actual answer is that H2O2 has a weak O-O single bond, plus it can react to form water – a very stable substance. So a low barrier to reaction plus a big increase in stability after it has reacted.
The danger is more from the fact that cells and tissues contain lots of delicate stuff like cell membranes. Oxidation of any chemical changes it’s properties, and something so specialised like a cell will likely not function afterwards. The human liver is effectively a giant oxidising machine, and historically scientists have used dried and ground-up pig liver to do some pretty amazing reactions.
H2O2 is very useful in the chemical industry, and is common in cleaning solutions and hair dyes.
Think of the atoms as letters, with which you make words – and the words are completely different meanings than the letters themselves. And the sake letters, arranged differently, also mean different things.
So its not only the letters, but how many and how they are arranged.
Carbon is harmless, nitrogen is harmless, add them together it becomes CN – and you just got the cyanide radical that will kill you very dead very fast. Add a little hidrogen to carbon – CH4 – you got methane. Do that to Nitrogen – you got ammonia which is *very* different.
Think of a compound as its own new thing, not the mix of others.
Because that extra oxygen doesn’t really wanna be in peroxide that much. It rather oxidize something around it and leave a stable and harmless water behind.
H2O2 may seem like it should be similar to water, given that has only one additional oxygen atom, but it actually belongs to a completely different class of molecules.
The key is to look at the bonding. H2O’s bonding looks like: H-O-H. The dashes represent electrons shared between the atoms. The O-H bonds turn out to be pretty stable because oxygen is naturally “electron loving” and hydrogen is naturally “electron hating” (in chemistry it is called electronegative and electropositive), so they end up making a happy couple. Imagine a relationship where one partner loves to cook and the other partner hates to cook, it’s a win-win scenario to let the first partner cook and have the other partner do something else like mowing the lawn
On the other hand, H2O2’s bonding looks like: H-O-O-H. It contains an O-O bond, where two “electron loving” oxygen atoms are competing for the same electrons. This is a highly unstable relationship. In the couple analogy it is like two partners who both love cooking so much everyday that they get in each other’s way, can’t agree to share the cooking utensils, and make a complete mess of the kitchen. They end up hating each other and will likely breakup at some point.
The O-O bond is similarly unstable and likely to break. And after the breakup, the two oxygen atoms are each going to be desperately looking for a new relationship, maybe with some hydrogen atom that is more compatible. This makes them highly reactive and potentially dangerous for the human body because they might steal any hydrogen atom from tissues and organs that they can find and create a lot of damage
It is like changing the the word “kill” to “skill” by adding an “S”. In chemistry adding another atom to a molecule is significant to it’s shape and it’s ability to react with other compounds, especially those found in the human body.
Lethal? I drink it all the time, it’s the sequel to water!
I haven’t seen anybody else explicitely pointing it out: if you can’t write chemicals formulas with subscripts, you should instead use regular number, not superscripts.
H2O or CO2 are fine. H₂O and CO₂ (I hope these formulas are displyed correctly – with the “2” a bit lower and smaller than the letters) would be better, but “H²O” and “CO²” look terribly wrong to chemists.
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