IGCSE CHEMISTRY Determining Valence of Elements & Radicals

welcome to the first series of the topic construction of formulas and equations construction of formulas and equations is a very vital aspect in chemistry it is a prequisite to the fundamental of General chemistry and directly a basic requirement to understand ometry and More Concept to successively construct formulas and equations there is need to First understand how to determine and know the valencies of elements and other reacting species therefore the main objective of this lesson is to Define valency to understand how to determine the valencies of elements and radicals so let's begin by defining the term valence valency is the number of electrons an element needs to achieve an octed configuration in simpler terms valency is the combining power of an element let's look at this illustration to understand the definition so we have said valency is the number of electrons and elements needs to achieve an octet configuration now if you do remember that on the periodic table we've got metals and non-metals so just roughly if you can visualize the general structure of the periodic table we have a zigzag line that differentiates the nonmetals and the metals on the other side here you do realize that the metals they have fewer electrons in their outer shell therefore it is easier for them to lose those electrons in order to remain with an octed configuration on the other hand the nonmetals have got a lot of electrons compared to what they are lacking therefore it is easier for them to gain electrons that is why the valency can be restated as the capacity of an atom to give accept or share electrons to achieve an octed state so what we are saying is there are some methods like for example which have got fewer electrons in the outermost shell such as one two and three and these ones they can easily lose the one that they have when they lose that the fewer electrons in the outermost shell they are going to lose the entire shell all together therefore the next Shell that is going to remain is going to have eight electrons hence octed configuration but we also have elements that have got a lot of electrons like in the case of the nonmetals these ones they are supposed to gain because for example chlorine here it has seven of them so for it to be eight it only needs uh one more therefore it will be easier to gain that one than to lose the seven therefore in this instance it will gain electrons and we say it has accepted we also have unique cases in the case of carbon where these ones they do not need to lose or gain but what they need is to share hence we are saying this definition in the dialogue box here is actually a complete box where we are saying is the capacity of an atom to give accept or share electrons in order to achieve the octet configuration so that is the definition of of what valence is just to sort out the confusion there is a difference between valency and valency electrons these two things are closely related but there is a bigger difference let's look at this diagram here to fully understand the difference between the two now we are saying valency electrons is just simply the number of electrons in the outermost shell of any element whereas valency is the number of electrons that an atom can lose gain or share during a chemical reaction now for certain groups like groups one group two and group four as you will see soon these ones here you discover that the valency electrons and the valency will be the same thing however for groups five six and seven this is not the case valency and valence electrons are different so please take note that valence electrons simply refers to the total number of electrons in the outermost shell whereas valency is the electrons that an element can either accept lose or share in order to obtain an octed configuration which is simply the total the total number of eight uh electrons in the outermost shell with this background let's go ahead and look at how we can determine the valency for elements in groups 1 2 3 and four in these groups we are saying the simple rule for determining the valency of elements in these groups is that group number is equivalent to valency that is to say if something belongs to group one it means they have a valence of one those that are in group two all those elements they have a valence of two all the elements in group three they have a valence of three all the elements in group four have a valence of four let's look at a few examples here sodium is found in group one therefore it's going to have a valency of one magnesium is found in group two therefore it's going to have a valence of two aluminium is in group three aluminium is in group three therefore is going to have a valance of three carbon is in group four therefore it is going to have a valence of four let's look at how we can determine the valency for group for elements in group five 6 7 and 8 we are saying for this group for these groups valency is given by subtracting so here's the formula we're saying subtracting the group number of the given element from eight and this is because eight is the oate configuration so what we are saying is valency is equal to 8 minus the group number of the element in question for example if we are looking for something that is in group six then valence here will be equal to 8 - 6 which is equal to 2 if you're looking at the valence of something in group seven then valency is equal to 8 - 7 which is equal to 1 let's look at this one so we are saying valency is equal to 8 - group number which means if you're looking at group five then Valance will be 8 - 5 which would be a three if you're looking at group six then valency will be equal to 8 - 6 which is a two if you're looking at group seven then Valen is equals to 8 - 7 which is equal to 1 if you're looking at group 8 then valency is equal to 8 - 8 which is equal to 0 so all we are saying is the elements that are in group eight are stable because they don't have valency electrons a few examples here we have nitrogen which is in group five so nitrogen is group five that's why we are saying it's 8 minus 5 giving us a three we look at oxygen which is in group six so it's going to be 8 - 6 which we find to have a valence of two let's look at how we determine the valency for transition elements so we are saying transition elements have no fixed valences but V variable meaning the same element can have more than one valence for example ion can have a valence of two or three to uh to identify the valency for transition element check the number given in Roman numeral in the brackets let's look at the examples that we have here we want to we know that ion is a transition element so the name of the compound here is Ion 2 sulfate we can see in the brackets here we've got Aroma numeral two so this two simply represents the valency for this transition element here please do not confuse it it will not belong to sulfate but it will belong to the transition element so the first thing you're supposed to do is to actually find out which one is the transition element the same ion here it is called ion 3 again pay attention to the brackets that are here and what Roman numeral is inside so you find that here the valance is going to be three here the valance is going to be two so these valences that are put in Brackets as Roman numerals they belong to the uh transition element the last one says what is the valence of copper in Copper 2 carbonate again when you check in between here there is a Roman numeral of two in the bracket and the only transition element here is copper therefore the valence here also is going to be two let's look at how we determine the valency for Radicals now a radical is a group of atoms which is present in several compound but is incapable of independent existence which means these guys they exist as a group and the way they exist is the way they should exist so for the viance of radicals you simply need to master them as stipulated in any approved textbook for chemistry now most of them that you're going to find in either igcc or ecz and most of the syllabus that we have the syllabi that we have these are the ones that are common so here we have ammonia chlorate chloride hydroxide nitrate nitrite and these are the formulas respectively so ammonia has got a formula so this is ammonium has got a formula nh4 and it has a valence of of one so all these that are in this box here the first box here so all these that are in the first box here they have a valance of one so for Radicals you are supposed to memorize their name their formula and their valency this is going to be helpful as you navigate through the course of chemistry chlorate has got C3 valence is one check on the carbonate see a carbonate has got CO3 and the valence here is two so all these that are in here they have a valence of two then for the phosphate which is alone here it has got a valence of three so this table all we are saying is you are supposed to memorize it now the challenge we are giving I'm giving to you guys is can you come up with a pneumonic on how you can memorize all these uh radicals in their order once you master these radicals you are warm and dry everything will become simplified ifed for you let's look at the summary when it comes to determining valencies so we said from groups one they have a valence of one group two they have a valence of two which means berum has a valence of two magnesium two calcium two strum two barium two and radon is two so all the elements that are in this group they have a valence of one all the elements that are in group two they have a valance of two in group three they have a valance of three in group four they have the valance of four and this is as a result of sharing then as you skip you go to group five 6 7 and 8 if you want you can see that the numbers they start reducing decreasing so we started from Valance is one Valance is two Valance is three Valance is four then again we go like 3 2 1 Z so you can memorize it like that it's fine that's why we say the periodic table is a very important ingred ingredient in everything that we do so then the last part we looked at was the transition element with the transition elements in this block or the elements in this block which have a valencies that are variable it can either be one or two depending on the compound in which it is combined then we talked about radicals which we are only supposed to memorize so please please this is going to be very important go through this video share it with your friends go over and over and once you understand valences everything that will follow will be a piece of cake thank you so much enjoy watching other lessons