imagine you're at a party full of people constantly making and breaking friendships each person there is social in their own way some like to make many friends While others prefer just a few some create balanced friendships and form a tight-knit group While others are a bit more one-sided and may break up as drama ensues this Dynamic Social Scene is a lot like the world of chemical reactions and in this video we'll explore how calent bonds are formed and broken and delve into the Intriguing world of radicals and their reactions coent bonds are broken and formed during chemical reactions atoms will form calent bonds to try and fill their outer shell of electrons and become more stable they do this by sharing a pair of electrons between them often bonds will form from unpaired electrons from either atom as we just saw we'll call atoms like this radicals as they're typically highly reactive and unstable radicals can be charged but they're often uncharged as is the case here when we draw reaction mechanisms the sharing of unpaired electrons is indicated by a half Arrow or a fish hook from each of the reacting radicals the other valence electrons called lone pairs don't usually need to be drawn since they're not particip ipating in the reaction a bond may also form when one atom shares an entire lone pair of electrons with another which will indicate using a full or curly Arrow here the electron donor is termed the nucleophile in the electron acceptor the electrophile notice that the lone pair is drawn as two dots on the nucleophilic atom and that our curly arrow is drawn from the nucleophile to the electrophile when a bond is broken the bonding electron pair may be divided between the two atoms in the bond where each atom receives one unpaired electron making it a radical this process is called homolysis or homolytic fision and is indicated by two half arrows drawn from the bond to each of the bonded atoms if the bond is polar the bonding electrons are more strongly attracted to the more electronegative atom so when the bond breaks the electronegative atom May receive both of the bonding electrons and gain a negative charge the electropositive atom receives no bonding electrons and gains a positive charge this process is called heterolysis or heterolytic fision and is indicated by a full curly Arrow drawn from the bond to the more electronegative atom for now we'll focus more on homolytic Vision in the subsequent reactions that occur with the radicals that are formed reactions between radicals will play an important role in our atmosphere radicals are often formed when a molecule absorbs U light causing a calent bond to undergo homolytic fision for example CO2 absorbs EV light to form two chlorine radicals we'll come back to these radicals in a second but for now note that when we draw our lone pairs of electrons we see that our chlorine radical is simply a neutral chlorine atom with seven electrons in its outer shell but radicals can also hold charge and we see the importance of this in the context of mass spectrometry positive radical cations for example are formed when an electron is removed from a neutral molecule during the ionization step of this process for example we can see this happen with methanol the charge of this radical cation then allows it to be deflected by a magnetic field helping to provide a measurement of its mass also in the ionization step of this process process we can form negative radical anion by adding electrons to a neutral molecule for example the super oxide ion O2 minus is formed by adding an electron to a neutral diatomic oxygen the resulting molecule contains two oxygen atoms with one calent Bond and one unpaired electron going back to reactions between radicals we see radicals play an important role of the breakdown of ozone in the atmosphere ozone is a molecule consisting of three three oxygen atoms the absorption of UV light by ozone will cause the molecule to undergo homolytic fision and produce an O2 molecule and an oxygen Radical by doing this the ozone layer helps protect us from damaging Rays created by the sun in the more recent context of human history the reduction of the ozone layer has been partially caused by the introduction of chlorofluorocarbons or cfc's into the atmosphere CFCs are commonly used in aerosols refriger and fire suppressants and can produce chlorine radicals when exposed to UV light in a process similar to what we saw before we see the homolytic vision of a carbon to chlorine bond produce a chlorine radical note that Florine radicals are not formed as the carbon to Florine bond is much stronger than the carbon to chlorine bond we call this reaction the initiation step as the production of chlorine radicals will set off a chain reaction this radical can react with an ozone molec to produce O2 and a new radical containing chlorine and oxygen the chlorine oxygen radical can then react with another ozone molecule to form two more molecules of o2 and regenerate the chlorine radical a reaction like this where a radical is consumed and a new radical is then formed is termed a propagation step as it creates a chain reaction this reaction can be terminated when two of our chlorine radicals react to form a non- radical chlorine molecule bringing an end to our Chain Reaction the overall equation for this reaction is similar to what we saw before with the destruction of ozone with UV light however the chlorine radicals here provide an alternative reaction pathway and increase the rate of this reaction the chlorine radical therefore acts as a catalyst and in doing so makes the introduction of CFCs into the atmosphere particularly devastating for the ozone layer are also involved in the conversion of alkanes to halogeno alanes these reactions usually take place in the gas phase for example methane can react with chlorine to produce chloromethane D chloromethane Tri chloromethane known as chloroform or tetrachloromethane the equation for the first of these reactions shows the transformation of methane and chlorine to form chloromethane and hydrochloric acid just as in the destruction of ozone this mechanism can be divided into initiation propagation and termination steps in the initiation step we have the homolytic fision of chlorine to form chlorine radicals these radicals create our Chain Reaction propagated by the reaction with methane to create a methyl radical this process is terminated when the methyl radical joins with the chlorine radical to produce chloromethane free radical substitution reactions like this can produce a range of products prodcts and can be difficult to control in this process if there were additional chlorine radicals to react with the products of our termination step could have created another Chain Reaction leading to The Unwanted production of tetrachloromethane in summary we've uncovered the fundamental principles of calent bond formation and breaking largely in the context of the production of radicals and their various uses we learned that calent bonds are formed when atoms share electrons and these bonds can break to processes like homolytic fision or heterolytic fision we also explored the dynamic world of radicals and their crucial roles in atmospheric chemistry and the free radical substitution of alkanes understanding these Concepts allows us to gain insights into the molecular mechanisms that underpin everything from the depletion of the ozone layer to the production of everyday chemicals Mastery of bond formation breaking is a Cornerstone of chemistry empowering you to tackle more complex reactions and applications in future studies