hello this is dr hannah asil and today we're talking about group seven halogens and this is for the ias chemistry so you remember that halogens are in group seven uh fluorine chlorine bromine iodine and at the end there is acetylene remember that as we go down the group the atom gets bigger more shells more electrons so the atomic radius increases as we go down and we said that has to do with the reactivity in the reactivity at the top is more reactive so fluorine is a more reactive oxidizing agent because it's a smaller atom um it is more likely to accept electrons and the electron that is being gained will have a stronger attraction to the positive nucleus since it is nearer to the nucleus as we go down the atom gets bigger so it becomes less reactive as a non-metal or a less reactive oxidizing agent since it will be more and more difficult to attract an electron to the positive nucleus that is further away then we said if we're talking about boiling point then going down the group fluorine chlorine bromine iodine these are bigger molecules what kind of intermolecular forces between them you should realize that they only have london dispersion forces or van der waals forces and these increase in strength as we go down the group because the larger atom will have more electrons so stronger london dispersion forces that will need more energy to be broken so as a molecule of fluid including bromine and iodine the um boiling point or melting point boiling point uh increases as we go down the group now if we're looking at appearance we said fluorine is a yellow gas as we go down the group the boiling point increases and the color gets darker so chlorine is a green gas bromine is a reddish brown liquid and remember that this is the only liquid non-metal in the periodic table and then we said iud now iodine as a solid it's a gray salt when we dissolve it in water it is a reddish-brown solution but you have to remember that when we dissolve it in an organic solvent such as hexane it is purple in color and the hexane or the organic solvent has lower density than water and that means if i have an aqueous solution of iodine that means the iodine dissolved in water first of all the aqueous solution is reddish brown and it will be below the layer of hexane the iodine dissolves in hexane to form a purple color and this has lower density than water so it will float on the top of what please pay attention to that then as we go down astatine is a black solid okay if we're looking at hydrogen halides h f h c l h b r h i again as we go down the group the halogen atom gets bigger and that means the bond between the h and the f will get weaker as we go down since the bonding pairs of electrons are less strongly attracted to the positive nucleus that is further away as we go down so this bond will need lower bond energy and the one at the bottom of the group will be less thermally stable it will also have to do with the acidity now each of these should dissolve in water and ionize to form h plus ions but the bond that is weaker as we go down will be more easily broken so it will ionize more easily and that means that the hi is a more acidic solution than the hf okay boiling points of the hydrogen halides now we said boiling points of uh the halogens alone fluorine chlorine bromine iodine as we go down the group it increases but then if we have hydrogen halides we have another factor as you see the hf is the one that has higher boiling point and then as we go down hcl hbrh the boiling point increases now why is that mainly because of the type of intermolecular forces now the hf is the only one in that list that can do hydrogen bonds due to the strong electronegativity of the chlorine atom so chlorine is very electronegative the bond will have a permanent dipole dipole and the molecules will have permanent dipole-dipole interactions and of course the weak van der waals forces but they will also have hydrogen bonding between the molecules and we said hydrogen bonding needs more energy to be broken so the hf has higher melting point or boiling point than the other hydrogen halides now as we go down hcl hbrhi please do not say that they form hydrogen bonds because we don't regard them as forming hydrogen bonds since it is very very uh weak they do have permanent dipole-dipole interactions they have van der waals forces but as we go down the increasing number of electrons in the halogen uh causes stronger van der waals forces between the molecules and that means that um the boiling point will increase as i go from hcl hbrh i remember that the electronegativity also decreases so as we go down actually the dipoles become weaker so because chlorine is more electronegative than bromine more electronegative than iodine so the electronegativity of the atoms decreases and that means that the permanent dipole-dipole interactions will decrease but the number of electrons increases so stronger van der waals forces higher boiling point as we go down so remember that hf is higher and then we have hcl hbr hi in increasing boiling okay so let us take a look at the reactions of the halides with aqueous silver nitrate if you remember from the o level we said to test for chloride bromide iodide i need to add what i need to add dilute nitric acid and silver nitrate solution with chloride i have white precipitate with bromide i get a cream precipitate with iodide i get a yellow preset so this is what we said in o level but then as you notice the colors are very close to each other and when we're actually doing this test it is very hard to determine if the precipitate is really white or cream or yellow so we need to move on and do another test on that precipitate to determine if it is actually chloride provide or i write so what we do is the the first thing we do is we should try to dissolve the precipitate that we get in dilute aqueous amount if it dissolves in dilute aqueous ammonia it is chloride because you know that the silver nitrate with any chloride form silver chloride which is the white perceptive now if we this silver chloride can dissolve in dilute aqueous ammonia or of course concentrated aqueous ammonia to form what we call a complex and this is soluble in water so if the white precipitate dissolves in dilute aqueous ammonia it is chloride if it doesn't then i try concentrate now both bromide and iodide will be tested with concentrated aqueous ammonia the bromide dissolves the iodide does not so remember for all of these we add dilute nitric acid and silver nitrate the precipitate that comes out if it is soluble in dilute aqueous ammonia it's chloride if it dissolves in concentrated aqueous ammonia it's bromide if it doesn't dissolve in any of that then it is iodine okay another reaction of halides is with concentrated sulfuric acid you need to remember that when a chloride potassium chloride or sodium chloride whatever reacts with concentrated sulfuric acid it gives white fumes this is because we get hcl gas and there is no further reaction no further reaction because hcl is a weak reducing agent it does not go on and react with sulfuric acid so please remember that with chloride and concentrate sulfuric acid we only get hcl and that's it but then if we do bromide actually the hbr that comes out from the reaction goes back and reacts again with sulfuric acid because it is a stronger reducing agent so it reacts again with sulfuric acid and what we end up with is sulfur dioxide and bromine so remember with chloride we get only hcl with bromide the hbr reacts again to give so2 plus bromine now with iodide because the hi is a very strong reducing agent it continues to react to the sulfuric acid so the hi that is formed at the beginning reacts with sulfuric acid again to form it could form sulfur dioxide iodine sulfur and h2s which is hydrogen sulfide and you should realize that what you will get is you could get a yellow solid so the yellow solid will be due to the formation of the sulfur and smell of rotten eggs due to the formation of the hydrogen sulfide do we understand that so the hi reacts several times with the sulfuric acid to give a lot of products because it is a very strong reducing age reaction with aqueous potassium hydroxide and remember that this is the same as reaction with aqueous sodium hydroxide so he could be telling you that we're reacting chlorine for example with potassium hydroxide on cold or hot concentrate in both cases they give different results now when we're reacting chlorine with potassium hydroxide on coal it will form potassium chloride potassium hypochlorite and water so kcl and kclo and remember when we were doing uh equations we said this is an example of a disproportionation reaction in which chlorine goes from 0 to -1 oxidation number and that means it is reduced it also goes in the same equation from zero to plus one oxidation number and that means it is oxidized and we said if the same element is oxidized and reduced in the same reaction this is called a disproportionation reaction now with the hot concentrated potassium hydroxide it will give kcl and kclo3 this is called potassium chlorate so the chlorine changes from oxidation number zero once to minus one and one's two plus five please know these reactions you will be asked about another disproportionation reaction is when the chlorine reacts with water again when chlorine reacts with water this will give two types of acids hcl and o c l so the chlorine changes oxidation number from zero to minus one reduction and once from zero to plus one oxidation so again this is another example of this proportionation the action of the hydrogen halides with ammonia remember that we said the hydrogen halides are acidic ammonia is a base so they react to form a salt which is ammonium something ammonium halide salt if we are reacting hydrogen halides with water dissolving any hydrogen halide in water will produce acids so they will ionize you can either say the hcl ionizes to h plus and cl minus or you can say it reacts with water to form what we call the hydronium ion h3o plus plus the cl max another reaction of halogens is we know that halogens are reactive non-metals so they will react with group one and two metals to form ionic compounds and again this is an oxidation reduction reaction because the uh metal group one of group two will lose an electron the uh halogens gain electrons and remember that when we were doing balancing or writing overall ionic equations we need to make the number of electrons the same on both sides so this would be the overall ionic equation two sodium plus cl2 to get to any plus plus two cl are we okay so far let's do some questions and answers very quick now this is the first question on this topic which test is used to show that sodium chloride solution contains chloride ions of course you should remember that the test for chloride ions is dilute nitric acid and silver nitrate to give a white prism so that's easy when chlorine is reacted with hot concentrated potassium hydroxide the chlorine undergoes this proportionation what are the oxidation states of chlorine in the product so again let's remember here is reacting the chlorine with hot concentrated we said hot concentrated will give the kcl plus the kclo3 so the oxidation numbers change to minus 1 and plus 5. what are the gaseous products formed other than water vapor when concentrated sulfuric acid is added to potassium bromide so remember when we're reacting it with the bromide we said it will form hbr and then the hbr will go back and react to form so2 and vr2 so my products would be bromine hydrogen bromide and sulfur diets okay on adding chlorine to aqueous sodium bromide the resulting solution is what remember that which one is more reactive chlorine is more reactive than bromine so when we react chlorine with sodium bromide the chlorine displaces it forms bromine what was the color of bromine reddish brown so that is the color of the resulting solution two layers form when nonpolar solvent cyclohexane is placed with a dilute solution of aqueous iodine and left to stand again we said if i have an aqueous solution of iodine it is yellow or orange in color now if you're going to add cyclohexane and organic solvent we said the iodine will dissolve in it first of all to form purple color and then we said the cyclohexane has lower density than the solution so the purple color will be the upper layer and the yellow color will be the lower leg given the following boiling temperature select the likely boiling temperature for hf remember we said what was the relationship of the boiling point we said the hf is the only one that is regarded as having hydrogen bonding so it has much higher boiling point than the others and then the others increase in boiling temperatures because more electrons so stronger van der waals forces so which one would be the likely boiling point of hf it should be higher than all of these due to the presence of what due to the presence of hydrogen bonding so we would choose 293 as the likely uh boiling point which observations about silver chloride and silver bromide are correct now action of sunlight i want you to remember that this we did in or level when we said the effect of light on reactions silver ions are white or colorless now if you put them in sunlight all the silver compounds will uh have the silver ions taking electrons so they will form silver and silver is gray so this will happen for any of the silver halides so actually both silver chloride and silver bromide if you leave it in sunlight they will both turn gray now the action of dilute ammonia we said which one will dissolve in dilute ammonia the chloride is the only one that dissolves in dilute ammonia do you remember that please keep all of this in mind a solid silver halide was tested the silver halide is which one action of sunlight it turns gray when we said all of them turn gray action of dilute ammonia it does not dissolve if it does not dissolve then it's not wet then it's not chloride because we said the chloride would dissolve so if he says it does not dissolve that means it's bromide or iodide now when he added concentrated ammonia the solid dissolved well which one will dissolve in concentrated ammonia we said the bromide would dissolve so my answer is silver bromide because the solid dissolved in concentrated ammonia if it were are you died we said iodide gives a yellow preceptor that does not dissolve in dilute or concentrated the most significant factor determining the trend in the rate of hydrolysis of halogenobutanes we said what determines the rate of breaking down of halogenobutanes halogenobutanes means alkanes with halogens c halogen bond so what determines the strength is the bond strength of the carbon halogen bond okay at room temperature iodine is a solid bromine is a liquid what was the explanation for this we said as we go down uh the group the boiling point increases so bromine is a liquid iodine is a solid why is that we said this is due to the weak intermolecular forces that get stronger as we go down the group so it is actually because iodine has stronger london forces remember um they don't have permanent dipoles at all okay and we don't say it's because bromine is more volatile that's wrong wrong he's saying why is it solid and liquid and so on so it is because iodine has stronger london force potassium halides can all react with concentrated sulfuric acid to produce what what do all of them produce kcl or kvr or ki they all produce hydrogen halides because the first thing that will happen when you react any of these with sulfuric acid is it will give hcl or hbr or hi now which one of the following substances forms when a few drops of concentrated sulfuric acid is added to sodium chloride again i am going to add sodium chloride this gives the sodium hydrogen some fate as my product equal amounts of one chloro and one iodo butane are warmed with silver nitrate in the presence of ethanol why does one chlorobutane react more slowly remember we said if i have c cl or c i which bond will break more easily we said as we go down the halogen is a bigger atom so the bond is weaker and will break more easily and that means that the ccl bond is stronger than the ci bond a halogen dissolves in water to form a yellow solution and in cyclohexene to form purple which one did we say does that iud have to remember that which of the following describes the appearance of iodine under the stated conditions so he's talking about iodine as a solid it is what as a solid i would choose gray now dissolved in aqueous would be would be brown dissolved in liquid hydrocarbon it would be perp please follow all of them solutions of barium chloride and silver nitrate are mixed together the reaction that takes place is an example of what what happens if i add silver nitrate to something that has chloride he said it forms a white recipe so this type of reaction is precipitation which one of the following equations represents a halogen displacement reactions that can occur so for it to occur the halogen that is reacted with the potassium halide should be more reactive than that halide in the potassium ah a compound so which of these would react you should realize that chlorine is more reactive than bromine so you if you have kbr plus chlorine it would react the silver halide which is insoluble in water but soluble in dilute aqueous ammonia so it forms a precipitate in solution and then if you add dilute aqueous ammonia dissolves that is which of these the chloride remember that it is the chloride that will dissolve in dilute aqueous the equation for the reaction of chlorine with water is shown this reaction is an example of what remember we said this is an example of what the chlorine changes from oxidation number zero to minus one and zero to plus one so oxidation and reduction for the same element this is this proportionation reaction which of the following is not true of the hydrogen halides hcl hbr hr forms white smoke well you should realize that the hcl with ammonia remember all of these actually with ammonia would form a white smoke of ammonium compound because these are acids and they would react with ammonia so this is true dissolving water to form strong acids yes all of them form acids are usually prepared by the action of sulfuric acid on sodium halide that would not be true because we said the hcl does not react further with the sulfuric acid but the hbr would reduce the sulfuric acid the hi would react again so i cannot use this reaction to prepare hydrogen hair lines okay so what is observed with a mixture of bromoethane and aqueous silver nitrate now silver nitrate is reacting with something that has bromide remember we said bromide would give me a cream precipitate give the equation for the reaction between chlorine and sodium hydroxide that forms sodium chlorate you should remember that this is the one with the hot concentrated sodium hydroxide that forms naclo3 that is the sodium chlorate please do not forget that the equation has to be balanced which of the following reactions is the most likely to occur when chlorine uh sorry with chlorine in hot concentrated sodium hydroxide again with chlorine in sodium hydroxide concentrated will give nacl or this question says potassium bromide can be distinguished from potassium chloride by its reaction with silver nitrate followed by addition of aqueous ammonia solution state what you would see on the addition of silver nitrate to potassium bromide how could both dilute and concentrated ammonia be used to confirm that it is bromide rather than chloride so remember that when we add uh dilute nitric acid and silver nitrate to something that has bromide it gives a cream precept now this precipitate dissolves in concentrated ammonia but not dilute the chloride would form white precipitate that dissolves in both dilute and concentrated among the rates of hydrolysis of different halogenoalkanes can be compared by carrying out the reaction in the presence of aqueous silver nitrate when an iodo alkene is used the experimental observations would be remember with the iodide i get a yellow precipice chloride ions in solution can be distinguished from other halide ions by the addition of silver nitrate followed by dilute equals ammonia state what you would see again when it is added to chloride followed by dilute aqueous ammonia so what we have here is chloride with the silver nitrate white precipitate with dilute ammonia the precipitate dissolves now why the concentrated should not be used because both chloride and bromide precipitates would dissolve in concentrated amounts in the reaction of concentrated sulfuric acid with sodium iodide the sulfur is finally reduced to what so here we have sulfuric acid with iodide remember that we form so2 and s and h2s so which one do i have here in the end it would form h2s so hydrogen sulfide that's the final a solid is soluble in water produces steamy acidic fumes with concentrated sulfuric acid what would this solid b remember that with sulfuric acid if it gives white fumes it is sodium chloride aqueous silver nitrate can be used to test for the presence of bromide right an ionic equation includes state symbols so he's reacting silver ions with bromide ions remember that the silver ions are aqueous the bromide ions have a minus on top of that and that's aqueous the uh silver bromide sole that is formed is a precipitate or assault it can be difficult to distinguish between the colors of the silver halide so we use ammonia a silver halide dissolved in concentrated ammonia explain why this result does not prove that the silver halide was silver bromide and give a further test to confirm that the silver halide is silver bromide remember that we said if we add concentrated both silver chloride and silver bromide would dissolve so you should use dilute ammonia in that case if it is chloride it dissolves if it is bromide it would not dissolve thank you for listening i hope it was helpful and i hope you are able to understand all of this and uh please listen to the next video thank you