the learning objective of the topic is represent the relationship between potential energy and distance between atoms based on factors that influence the interaction strength so what is the meaning of interaction strength what are the factors that influence this thing and what is the relationship between potential energy and distance between atoms i'll be discussing all of this in this video hello everyone this is topic 2.2 intramolecular force and potential energy this is taken from ap chemistry college board so first of all let me tell you what does it mean by intramolecular forces whenever the atoms combine to form molecules there is some interaction between the two molecules so that interaction is called as intermolecular forces whereas the interaction which is present between the atoms that is called as intramolecular forces these forces are due to the bonds which are between the atoms these forces can be ionic bond or covalent bond we already know what is a ionic bond and what is a covalent bond so here let's see an example just to recall ionic bond is when one of the atom loses the electron and another atom gains that electron then an ionic bond is formed between those two atoms whereas covalent bond is due to the sharing of electrons for example here you can see that two chlorine atoms are sharing one electron each and forming a bond between them this is called a covalent bond between two chlorine atoms first we will see that what are the factors which affect the potential energy for a covalent molecule and the simplest covalent molecule i have chosen is h2 that is hydrogen molecule we already know that this hydrogen molecule is formed by the covalent bonding between two hydrogen atoms and we suppose here that first hydrogen atom is h a and another hydrogen atom is hb there is an attraction between the electrons and the protons because electron is negatively charged and proton is positively charged so this electron is strongly attracted by the nucleus this kind of attraction is present in both the hydrogen atoms apart from that there is a weak attraction between the electron of first atom with the nucleus of second atom when these atoms will come closer this e a will be attracted towards the nucleus of hydrogen b similarly electron of atom b will be attracted towards the nucleus of atom a when these atoms would be very close to each other there will be repulsion between both the nuclei so here this graph shows that how the potential energy varies when a hydrogen molecule is formed from two hydrogen atoms we know that hydrogen atom has one s orbital which has one electron when one is orbital of hydrogen 1 will interact with 1s orbital of hydrogen 2 the h2 molecule will be formed due to the overlapping between the electron cloud of both the hydrogens and this will lead to the formation of a sigma bond or you can say single bond between the two hydrogens this is a graph between potential energy and the internuclear distance internuclear distance means the distance between the nuclei of both the atoms so when these two atoms are very much far away from each other at that time the potential energy is zero but as they start coming close to each other the interaction between both the atom's star i already told you that the electron of one hydrogen atom would interact with the nuclei of another hydrogen atom as there is an attraction between both these atoms this leads to decrease in the potential energy as you can see here and when the internuclear distance between both the atoms is 74 picometer at that time the potential energy is minimum but when internuclear distance between both the atoms decreases further at that time the repulsion between both the nuclei starts and you can see here that due to the repulsion the potential energy starts increasing the distance where the potential energy is minimum both hydrogen atoms are at such a distance that the hydrogen molecule has become stable the internuclear distance is 74 picometer the potential energy at this point is minus 432 kilojoules per mole the x axis where the potential energy is minimum at that point the internuclear distance is called the bond length and the y-axis where the potential energy is minimum that energy is called as bond energy or bond enthalpy now this bond length and bond energy both depends on the size of the atoms and the nature of the bonds if we want to calculate the bond length for two atoms what we do is the radius of first atom plus the radius of the second atom that distance is called the bond length for a covalent molecule what are the factors which affect the bond length first discuss how the size of atoms affect the bond length we are comparing three types of covalent molecules first is hf then fcl then hbr the difference between these three molecules is the halogen atom first is fluorine then chlorine then bromine as we go from fluorine to bromine the size of the atom goes on increasing when the size of the atom increases that atom would be far away from another atom and that is why the bond length goes on increasing as we are moving towards the higher size second factor is multiplicity of bonds it tells that it is a single bond double bond or a triple bond if the multiplicity is one then it means single bond if multiplicity is two then it means double bond and if it is three it means triple bond when we are moving from single bond to triple bond here shared number of electrons is two for double bond the shear number of electrons is four and for triple bond the shared number of electrons is six number of electrons shared is increasing and that is why the attractive force between the electrons and nuclei increases for the single bond the attractive force between the electron and nuclear is smallest out of these three and for the triple bond it is the highest more is the attraction lesser is the bond length because the atoms would be closer to each other so that is why when we are moving from single bond to triple bond the bond length is decreasing so these were the factors which affect the bond length what is bond enthalpy or bond energy as i told you in the graph also the minima of the potential energy tells that how much is the bond energy so bond energy is actually the amount of energy which is required to break one mole of bonds between two atoms so if we give that much energy to a bond the bond would break so this bond energy or bond enthalpy is in kilojoules per mole and it is an endothermic process because the bond is breaking so we need some energy to break that bond the bond enthalpy increases with multiplicity of bond as we are moving from single bond to triple bond the attraction between both the atoms is increasing and that is why the energy required to break that bond would also increase for single bond between two carbons the bond energy is 346 kilojoules per mole and for triple bond it is more than double the bond enthalpy is also affected by the length of the bond so if we are moving from hf to hbr i told you that the bond length would increase and as the bond length is increasing the bond would become weaker and the bond energy would decrease so for hf the bond energy is 567 kilojoules per mole for hcl it is 431 and for hbr it is 366 kilojoules per mole now let's see one of the question which is nitrogen is capable of forming single double or triple bonds and the figure that follows shows the potential energy as a function of internuclear distance for each of these types of bonds match the three curves in the figure abc to the three types of bonds so the question says that nitrogen can form three types of bonds single double and triple and here a graph is given between energy and the distance we can see that it is similar to that of the hydrogen molecule so we need to tell that which of these curves is for single bond double bond and triple bond the basic difference which we can interpret is the change in the energy for curve a the energy is maximum and for c it is lee so out of all the types of bonds triple bond needs the maximum energy so we can say that a curve is for triple bond b curve is for double bond and c curve is for single bond apart from that we can also interpret this graph with the help of distance we can see that the bond length for a is the minimum and bond length for c is the maximum the single bonds have higher bond length that is why the curve c is for the single bond and curve a is for the triple bond let's talk here about the ionic compounds for any compounds they are formed by the losing and gaining of electrons and so i have taken example of nacl here any that is sodium atom loses one electron and the chlorine atom gains that electron and a bond between sodium and chloride is formed sodium atom has a radius of 0.186 nanometers and the chlorine atom has a radius of 0.099 nanometer so sodium atom when loses the electron the size of the atom decreases because of more number of protons as compared to electrons here the radius decreases to 0.095 nanometers on the other side chlorine atom when gains the electron which is lost by sodium the radius of the chloride ion increases it becomes 0.181 nanometer and when we calculate the distance between sodium ion and the chloride ion it is addition of radius of both the ions here by adding both the radius we get the answer as 0.236 nanometers so the bond length between these two ions is 0.236 nanometers this is the way how we calculate the bond length for the ionic compounds now let's see how the potential energy changes for ionic bonds here you can see that the graph is same as that how we did for the covalent molecule when the sodium and chlorine atoms are very far from each other that time the potential energy is zero when the radius starts decreasing between both the ions the potential energy starts decreasing because of the attraction between both the ions but at a certain distance which is 236 picometers here between the ions the potential energy is minimum and on further decreasing the internuclear distance the potential energy starts increasing you can see here that when the internuclear distance is 180 picometers the potential energy has risen so the internuclear distance where the potential energy is minimum that is the bond length for the ionic compounds here also the y-axis tells about the potential energy so the point where the potential energy is minimum that tells about the bond enthalpy so let's see what are the factors which affect the lettuce enthalpy first let me tell you what is lettuce enthalpy ionic compounds form the lettuce so that is why the bond energy is called as lattice enthalpy for ionic compound if we see what are the factors which affect the lattice enthalpy the first factor is size of the ions here i have compared three compounds one is nacl then nabr then nai in all these three compounds the common ion is sodium and the halogen ion is changing from chlorine to iodine so as we move from chlorine to iron the size of the ions goes on increasing as the size increases the attraction becomes weaker between the cation and anion so due to this weaker attraction the lattice enthalpy decreases so there is a negative charge along with all these lattice enthalpies this negative charge tells that there is a attraction between both the ions we can see that for nacl the value is highest which is 787 kilojoules per mole and for nai it is the lowest another factor which affects the lattice enthalpy is the charge of the ion here i have compared the sodium magnesium and aluminium ions so as we are moving from sodium to aluminium the charge is increasing and due to this increase in charge the size of the ions decreases here aluminium ion has the smallest size and more is the charge there will be more attraction between the cation and anion and the lattice enthalpy increases so these are the two factors one is size of the iron and another is charge of the iron which affects the lattice enthalpies this explains that why magnesium oxide has exactly the same structure as sodium chloride but a much higher melting and boiling point because magnesium has higher charge than sodium and magnesium has smaller size than sodium ion the learning objective of the topic was represent the relationship between potential energy and distance between atoms based on factors that influence the interaction strength so i've discussed that how the potential energy changes with the distance between the atoms that was internuclear distance and i have also discussed that what are the factors which affect this interaction for covalent compounds it was the size of the atom and multiplicity of bond and for ionic compounds it was size of the ion and charge of the iron please like and subscribe to the channel log iota and press the bell icon