Straight-faced_solo: Short answer: because changing even one element in a compound will drastically change how it interacts with other chemicals.
Long answer: H2O is remarkable stable and wants to stay that way. H2O2 is still stable, but it will give the extra oxygen atom to any compound that it can, so it can be more stable. Unlucky for living things, cell membranes will end up taking this extra oxygen and they will no longer be able to hold their form. Once the cell membrane falls apart the cell will die.
Deano1234: WOOOOOW literally every one of these answers are wrong.
H2O2 does not kill cells with a free O atom going about grabbing up different things. In fact free O molecules happen all the time thanks to our Electron transport chain. It just bonds with H and creates water. The molecular structure of H2O2 is H-O-O-H, with those dashes being bonds. The middle bond is where the hydrogen peroxide breaks into two components producing 2 OH molecules. Now OH isn’t bad. In fact our body is full of OH- molecules. Water is constantly losing and gaining hydrogen. This gives a mixture in pure water of H2O molecules, HO- molecules and H3O+ molecules. This is the whole bases for the pH system (p=-log: 14= -log[H] + -log[HO-]). So why does H2O2 kill? The answer is quite radical! (you’ll see what I did there in a second)
When H2O2 breaks they create two OH radicals. A radical is any molecule with an odd number of electrons. So their is one unpaired electron in it. Molecules/Atoms HATE this. In the body biologists call these Reactive Oxidative Species (ROS). Radicals will then go through radical reactions with any molecule in their way. So these reactions caused by ROS are incredibly detrimental because by stealing 1 electron from another molecule the ROS stops being an ROS, but the other molecule becomes one, so the reaction is maintained. All cells do have mechanisms to address this because cells do create radicals all time, but by dumping H2O2 on cells it overloads the system killing the organism.
PrinceHawtbod: Basically H2O2 has the ability to form an OH radical. Radicals are molecules with an unpaired electron hanging around. Unpaired electrons are not stable so they attack other things, like cell membranes. So if they attack the cell membrane, everything leaks out which is bad news.
VehaMeursault: The difference is not gradual: changing one atom in a molecule changes everything about it.
Think of atoms like locks and keys, right? Some keys fit into some locks, and others don’t. Some keys fit into many locks, some keys only fit in a few.
Just like any key, these keys have teeth that allow it to turn the locks when they’re just right, or make the key absolutely useless. After all, you can’t just put any key into any lock and expect it to work, right?
Now imagine we take a key called “water” that we know fits almost all of the locks the make up a human body: it hydrates practically every cubic inch of your body, but only because it perfectly fits in all those locks, right? Now take all of those “water” keys, and of each you file away one tooth. What do you think happens? They don’t fit anymore! Your body isn’t getting hydrated anymore!
A small, gradual change (filing down or adding to a key’s tooth) can have *drastic*, fundamental consequences (no longer fitting a lock).
Adding or subtracting an element from a molecule changes he way it interacts with all other molecules.
JamesMercerIII: In water, oxygen is attached to two hydrogen atoms, like this: **H–O–H**. These hydrogen atoms are really just protons, and they don’t care too much about the electrons that they share with oxygen (the dotted lines in the picture above). This is why it’s easy for one to leave the electrons behind and go off and do its own thing (free hydrogen ions are what make things acidic). On the other hand, oxygen is an electron hog, i.e. it’s highly electronegative. It’s extremely difficult if not impossible to take electrons away from oxygen, like you can from hydrogen. (in chemistry, when we take electrons away from something it’s called “oxidation” because it’s what oxygen always does)
Hydrogen peroxide is a completely different molecule. Its structure is like this: **H–O–O–H**. That single bond between the two oxygens is not very strong. Each side of the molecule is pulling on that bond in the middle with equal strength. Because of the symmetry, when the bond breaks, you’re left with two molecules that have a *single unpaired electron*, because the bond itself was originally two electrons. Electrons don’t like to be unpaired, it’s a quantum mechanics thing. When peroxide decomposes, each oxygen takes one of the electrons from the original bond.
The two molecules it breaks up into are called hydroxyl radicals, and they look like this: **H–O***. That asterisk represents the unpaired electron. Now that unpaired electron is a huge problem. In fact, free radicals are pretty much the most reactive compounds known. It especially likes to find double-bonds or aromatic rings to attach to (ELI15). And guess what has lots of those? Pretty much all the most important biological macromolecules, like DNA and proteins.
It’s a really big problem when free-radicals can sneak past all your body’s defenses and damage DNA. Fortunately, your body has lots of ways of absorbing free-radicals. This is why it’s not a big deal to spill low concentration peroxide on your skin.
bchbtch: It changes the types of other molecules it will not interact with. It also changes how it will interact with them.
gingersqueaks1: Oxygen – oxygen bonds are weak and will break without much help and ‘attack’ other molecules.
luthorhuss: Chem professor used to give this great example: Na, sodium, is a silvery white solid that if ingested would kill you as well as explode. Cl, chlorine, is a toxic green gas that would burn your lungs and cause a horrible death. Put them together to get NaCl, salt, and if your body doesn’t get this, you die. Combinations and conformations make all the difference in chemistry.
RAGING_CATERPILLAR: In H2O2 the oxygen are in a condition that they haaaate (each having a -1 charge to balance out the hydrogen each having +1), making them willing to do way more to get out of that condition (react with another molecule, etc.).
In H2O oxygen is in its homey place with a -2 charge and is chill remaining that way (for the most part).
Taodragons: Me the first time I was introduced to chemistry;
So what you are telling me, is that hydrogen is flammable, and oxygen feeds fire, but together they put out fire? gtfo
cthree87: Imagine you added one more dot to the top of a lego block so instead of 8 dots they had 9. Now imagine trying to build something with them and some normal 8 dot blocks. How easy would it be to connect your 9 dot blocks to standard 8 dot blocks? They won’t connect!
Molecules work in a similar way. They connect or not with other receptor molecules in your body except h2o and h2o2 are going to connect to different things because of that one extra dot. What gets built when you try to mix in 9 dot blocks is extremely bad for you.
JNH1225: H2O is not “water,” H2O is the chemical formula of dihydrogen monoxide, a dangerous chemical compound.
Dihydrogen monoxide is colorless and tasteless liquid at room temperature. Studies have determined that 100% of humans who ingest, inhale, or make physical contact with any amount of H2O in any form, will die.
ImAFlyingWhale: Im sorry, but since when can hydrogen peroxide kill you?
Newbigin: H2O is AFAIK the most stable molecule there is. (In case I am mistaken here, it’s at least very stable). Meaning, that it’s formation brings a lot of energy and is favored in any reaction. On the other side, there are not many reactions able to split it or do anything dangerous with it. It is also a very polar molecule, with the oxygene been the center of the negative charge.
In H2O2, the two negative oxygens are next to each other and many substances can lead to a reaction that brings it to the mentioned, low level H2O molecule. Making it a very reactive molecule.
WRSaunders: Oxygen is dangerous, it’s what lets things catch on fire. H2O2 easily turns that extra O loose.