 In this video we are going to discuss a few problems on electronegativity. So let's look at the first question it says, electrons will spend more time around which are the following atoms in a covalent bond. Now to answer this question we need to consider the electronegativity of each of these atoms. Electronegativity is a measure of an atom's ability to attract an electron pair towards itself in a chemical bond. So if you have two atoms A and B and they share their electrons to form a chemical bond then electronegativity would determine around which of these two atoms the electrons would spend more time on. Like if A is more electronegative than B then the electrons would spend more time around atom A than around atom B. So basically it would become something like this. The electron pair is closer to A and farther from B. Now when we talk about the trend of electronegativity we know that electronegativity increases across a period. And this is because as we move across a period the number of protons in the nucleus increases and that means there is a stronger positive charge that can pull the electrons closer towards the nucleus. Now even though the number of electrons is also increasing as we move across a period it doesn't affect or offset our nuclear charge much because they are getting added in the same energy level. So basically it is this increased nuclear charge that attracts a shared pair of electrons towards the nucleus of an atom. And as a result electronegativity increases. So here we have lithium in group 1 and nitrogen, oxygen, fluorine and neons. So does it mean that neon has the largest electronegativity? No. You see neon is a noble gas with completely filled outer shell it has NS2-NP6 as a general electronic configuration and it has absolutely no interest in losing the stable electronic configuration by acquiring any more electrons. And this is why we don't consider electronegativity values for noble gases because they anyway don't form covalent bonds under normal conditions. So that means the atom with the highest electronegativity in this case is oxygen. And electrons will spend more time around oxygen in a covalent bond. Now remember guys this question has a basic assumption that these atoms are not bonded to a more electronegative atom. For example if oxygen was bonded to a more electronegative atom than itself like let's say fluorine atom then in this case electrons would obviously spend more time around the fluorine atom right? So here we assume that all the atoms that are given to us are not bonded to a more electronegative atom. Alright so let's look at the next question. In this question we are asked to consider the following NH, PS, SS and SBH bonds and the question is what is the correct order of bond polarity? Alright so here is the interesting word bond polarity. You see bond polarity basically refers to the unequal sharing of electrons between two atoms in a covalent bond and the magnitude of this unequal sharing is determined by the difference in the electronegativity that is bond polarity is proportional to delta En. Greater the difference in the electronegativity between the two atoms more polar the bond will be. When you look at these atoms you can see that they all belong to the same group. Nitrogen, phosphorus, arsenic and antimony they are all elements of group 15. And we know that electronegativity decreases as we go down the group. This is because as we go down the group newer and newer shells get added and as a result the outer electrons are farther and farther away from the pull of the nucleus. Not just that. The nuclear charge is also offset by the shielding effect of the inner electrons. As a result of this what happens is that the positive charge is not sufficient to attract the electrons in a bond and therefore the electronegativity decreases. Okay now if you look at the electronegativity values of these elements they would be 3.04 for nitrogen, 2.19 for phosphorus, 2.18 for arsenic and 2.05 for antimony. As you can see the electronegativity value indeed decreases down the group. And the electronegativity value for hydrogen is 2.2. So to figure out which of these bonds have maximum polarity or the correct order of bond polarity let's go ahead and calculate the electronegativity difference between the atoms of each of these bonds. So for NH delta EN, so we actually take absolute value here. Nitrogen is 3.04 minus 2.2 for hydrogen. That would be 0.84, similarly phosphorus delta EN would be 2.19 minus 2.2 which is 0.01. Let's calculate for the other two as well, 2.18 minus 2.2, 0.02 in the case of arsenic and hydrogen bond and lastly we have SbH that is 0.15. So these are the values of the electronegativity difference between the atoms of all of these bonds. Now based on this we can arrive at the correct order of bond polarity which is NH greater than SbH greater than AsH greater than Ph that is NH is the most polar and phosphorus hydrogen bond is the least polar.