you have probably heard about this word oxidation oxidizing or antioxidants and stuff like that but what exactly does it mean and what can you do knowing about it well let's find out oxidation has the word oxygen in it you can see that right so we can guess that it's probably got something to do with the oxygen right and that's how we defined it earlier not currently but that's how it started so let's start with that oxidation can be thought of as adding oxygen atoms for example take a look at these reactions what do you notice we see that like for example in this first reaction oxygen is getting added to magnesium right therefore we say magnesium is being oxidized or magnesium is undergoing oxidation remember oxygen is diatomic in nature that's why there's an O2 over here okay but the same thing happening over here look oxygen is being added to ion you can see that over here and therefore we say ion is being oxidized our ion is undergoing oxidation same thing over here oxygen look gets attached to carbon so carbon is being oxidized carbon is undergoing oxidation but a question I always had was well why do we give a name to these kinds of reaction what's so special about oxygen well I don't think there's anything special about oxygen but I think these these reactions are important for example if you look at ion oxide which we call it ION three oxide because the charge on the ion over here will be plus three we will get it to that but this is the molecule that you find in Rust this is rust I mean rust also involves water so the actual reaction also involves water molec UL over here but since rusting involves oxygen that's an important reaction for us because we want to prevent rusting and when you're burning stuff well guess what oxygen is involved combustion involves oxygen that's also another important reaction for us and so since these reactions are important and they involve oxygen that's probably the reason why we gave a name to it and we call it oxidation but anyways this was the earlier definition of oxidation later on we thought okay let's just think about what's really going on with the electrons over here so for example over here we realize when since magnesium is a metal it loses electrons in fact over here it's going to lose a couple of electrons and magnesium will now become magnesium 2+ because it has lost two electrons and oxygen well it gains two electrons and therefore oxygen becomes 2 minus and that's why they stick to each other okay this is how that reaction is formed so what we notice is that when magnesium is undergoing oxidation it's losing electrons well let's see if the same thing is happening over here well yeah ion is also a metal and it's losing electrons over here in fact ion loses three electrons to find form ion 3+ and that's why this is called ion 3 oxide because it has charge of 3 plus it has Lo it loses three electrons over here and oxygen gains those electrons I mean each atom of oxygen gains two electrons um making it oxygen 2 minus and so because oxygen has a 2 minus charge and ion has a three plus charge now you can notice three atoms of oxygen has total of minus 6 and two atoms of ion has a total of plus 6 plus 6 - 6 very nicely becomes neutral but again what's important is that ion which is undergoing oxidation is losing electrons and what about this one well this is actually a slightly more interesting case so we'll get back to it towards the end of the video but this means in most cases when you add oxygen to something that something loses electrons so we said hey hey hey oxidation is involving Lo loss of electrons so let's let's call that as the definition of oxidation and that is our new definition because it's generalizing the definition of oxidation we now say forget about oxygen items anything that loses electrons we will call it oxidation so magnesium is being oxidized because it's losing electrons ion is being oxidized because it is losing electrons that is the current definition of oxidation okay now if something loses electrons something else should gain electrons and in this case the oxygen is the one that gains electrons so we thought okay let's give a name to gaining electrons as well gaining electrons is what we call reduction and now immediately looking at this it feels weird right you're gaining electrons why do we call it reduction okay this sounds weird and there might be some history behind it we'll not worry too much about the naming and where it came from but here's how I think about it when you gain electrons since electrons are negative you are gaining negative charge okay and that means look at your charge your charge was zero to begin with over here oxygen has zero charge to begin with but now it has a negative charge that is in some sense reduction right it has reduced so gaining negative reduces your overall charge because you get more you gain more negative charge and so that kind of sort of makes sense to me so in you know in calling that reduction and so oxygen over here is getting reduced okay but of course what if we forget this how do we remember that oxidation is losing electrons reduction is gaining electrons there are a couple of pneumonics you can use for example one pneumonic that I like is Leo the Lion goes g here losing electrons is oxidation gaining electrons is reduction another pneumonic you can use is oil rig oxidation is losing reduction is gaining my friends keep debating about which one is better but I personally like to think in terms of charge when I gain electrons I gain negative charge and therefore it's a reduction and that's how I like to remember that gaining electrons is reduction therefore losing electrons must be oxidation but now we have multiple ways to remember whichever one works for you anyways now think about this if you have a reaction in which something is getting oxidized meaning something is losing electrons then something else must be gaining electrons so something else must be reduced and therefore such reactions in which something get oxidized and something else gets reduced we give a name to it we call them redox reactions because both reduction and oxidation must be happening and now here's my question do redox reactions need to involve oxygen the answer is no because our definition has become more General sorry oxygen but we don't need oxygen anymore any reaction in which something is losing electrons and something else is gaining electrons becomes a redox reaction so let's look at a few so here are a few reactions our goal now is to analyze each reactions and think about which one is undergoing oxid and which one is undergoing reduction so let me start with this one so we have ion that reacts with sulfur to give you ion sulfide so how do I know which is undergoing oxidation which is undergoing reduction well I know ion is a metal so it loses electrons so I just keep track of charge over here ion is neutral single atom of ion zero charge sulfur is also neutral zero charge sulfide usually sulfur gets a charge of -2 so Ion must have gotten a charge of plus2 meaning Ion must have lost two electrons sulfur must have gained two electrons giving you ion sulfide or we say Ion 2 sulfide but what's important for us is that look ion is the one that has lost electrons which mean ion got oxidized sulfur is the one that gained electrons and therefore sulfur is reduced again sulfur's charge has reduced sulfur is the one that underwent reduction now it be a great time for you to pause the video and try to analyze the remaining three reactions all right let's look at this one so sodium has a charge zero chlorine also has charge zero over here I know sodium is a metal so it's going to lose an electron in fact it loses one electron giving a plus one charge and chlorine gains an electron giving it negative one charge so look it's the sodium that lost electrons sodium got oxidized chlorine that gained electrons so chlorine got reduced all right here's the next one this looks slightly more complicated but we'll work it out silver being a metal over here loses electron so it all it loses one electron so it actually has plus one charge and sulfur gains two electrons means it has min-2 charge in fact that's the reason why we have two AGS so giving you plus two and min-2 that balances it out okay anyways that's the charge over here aluminium look it's not bonded to anything so it has zero charge over here but what happens over here hey now aluminium gets bonded to uh sulfur and aluminium is a metal it's the one that loses electrons and it usually loses three electrons so it gets + three and sulfur gets min-2 you can just look at the the molecular formula and also guess what the charge they must have had how many electrons they must have lost and gained and finally now look silver has is not bonded anymore so it has a zero charge so if you look at Silver it went from plus one to zero ooh ooh silver got reduced because its number has reduced it has gained electrons ah so silver under reduction what about aluminium aluminium look it underwent oxidation because look it it must have lost electrons so it has went from 0 to plus three so aluminium under went oxidation silver underwe reduction what about sulfur hey sulfur's charge has not reduced at all it has not sorry it has not changed at all so sulfur neither went oxidation nor reduction so this was an interesting one okay that brings us to the last one again if you haven't tried it feel free to try it now because this is an interesting one all right here it goes so sodium chloride we already saw plus one minus one charge um silver fluoride silver + one and Florine minus one uh sodium fluoride well sodium is again + one Florine minus one silver chloride so silver is + one chlorine is minus1 what do you notice which elements under oxidation which elimates underwe reduction none of them because none of their charge has changed which means that means none of them have lost electrons or gained electrons so this is not a redox reaction because nothing underwe oxidation nothing under reduction when I first came across such reactions I was surprised because in my mind any chemical reaction involves transfer of electrons so in my mind it was like every reaction must be redox reactions but right in front of your eyes you can see not every reaction is a redox reaction okay finally this brings us back to our carbon dioxide example why was this interesting you know well because in all these cases something was losing electrons and something else was gaining electrons right but over here carbon does not lose electrons to oxygen instead carbon and oxygen share the electrons forming a CO valent Bond so how does it make sense according to this new definition according to the current definition how does it make sense to talk about oxidation reduction over here well it is slightly more complex and interesting but here's the gist of it the electrons are not shared equally oxygen has a tendency to pull those electrons more towards itself compared to carbon we say oxygen is more electr negative electro negativity is the tendency of pulling the shared pair of electrons towards yourself okay so oxygen since it's more electronegative compared to carbon it pulls the shared PA of electrons more towards itself kind of hogs on those electrons and as a result oxygen also ends up getting a negative charge but not a complete negative charge because not a complete transport we say against a partial negative charge I know it sounds complicated but at the end of the day it's still kind of sort of getting a partial negative charge so in that sense it still makes sense to say oxygen is reduced and therefore carbon gets a partial positive charge meaning oxy oxidation carbon is oxidized okay so even here we can think in terms of oxidation and reduction anyways our last question could be what can we do now that we understand what oxidation reduction really is well here's an example now that we know that rusting is basically ion losing electrons to oxygen one way to prevent rusting is to coat it with a metal which loses electrons more readily compared to ion and one such example is zinc and that's why if you take an ion nail and you don't want it to rust we usually coat it with zinc it kind of gives you double protection first of all it kind of forms a barrier so it doesn't even allow oxygen to reach ion is the zinc that gets oxidized but even if there's a breach somewhere over here an ion is exposed even at that site of exposure oxygen is much more likely to react with zinc because zinc much more readily gives out its electrons compared to ion we say zinc is more reactive compared to ion so this using this knowledge we can protect our precious ion from getting rusted that's that's awesome right