Which solid has the highest melting point? Why? C(s, diamond), Kr(s), NaCl(s), H2O(s)

Video transcript

hey everyone in this example, we need to determine which of our given molecules has the lowest melting point. So we want to recall the trend that the greater the strength of our inter molecular force will correspond to a higher value for melting point based on our compound. So we're going to identify the inter molecular forces for our given compounds first beginning with C six H 12 06 which we should recognize as glucose. We're told that this is a solid molecule and we want to go ahead and recognize that we have nonmetal atoms being the carbon, oxygen and hydrogen that are bonded to hydrogen. And so we can say that therefore we have the inter molecular force which is hydrogen bonding, which we can say is a pretty strong inter molecular force, meaning that therefore the melting point is going to be a high melting point value most likely for this molecule. So let's go ahead and consider our next molecule, which is silicon dioxide. We're told that this is also a solid drawing out the molecule, we would have silicon in the center surrounded by two oxygen atoms. We should recognize that our oxygen atoms are more electro negative than silicon. When we recall upon our election negativity trend on the periodic table, which increases as we go from left to the top right of our periodic table. So we have di poles in the direction of our oxygen molecule. However, because we have these die poles and we have symmetry in this molecule where we have two oxygen atoms with these disciples, we have symmetry, so therefore the depos cancel. And so that means that we have a small election negativity difference between silicon and oxygen. And so we would have a non polar covalin compound, meaning that the electrons shared between silicon and oxygen and molecule are shared pretty evenly because we don't have these disciples since they'll cancel out because of the symmetry in the molecule. And so we can say that the I. M. F. Present. Sorry. So the I. M. F. Present. It's going to be Vander walls London dispersion forces. And sorry, let's make sure everything is in view. So we have the Vander wal's London dispersion force as our inter molecular force that is present here. And so this is a pretty weak inter molecular force. So we can say that therefore we should have a low melting point for this molecule. So moving on to our next molecule, we have magnesium to chlorine or chloride. We're told that this is a solid molecule. And sorry, so it's MG cL two. It's a solid molecule and we need to go ahead and recognize that magnesium based on its physician is a metallic atom. So we have magnesium which we can label as a medal bonded to a chlorine which we recognize based on its position on the periodic table is a non metal. So we have the combination of a metal bonded to a non metal. And so therefore this means that we have an ionic compound, meaning that these two atoms will have a transfer of electrons between one another which is why magnesium is charge, which is a two plus charge. Because we recall that magnesium as a group to a on the periodic table will therefore give those two electrons or rather borrow two electrons from our chlorine atom, which is why we have the two subscript next to the chlorine atom. And so because this is an ionic compound, we can say that the therefore the inter molecular force present is going to be our electrostatic inter molecular force, which we would recall is considered a week, one of the weaker inter molecular forces. And so therefore this compound will likely have a low melting point. So moving forward to our next compound, we are given the atom xenon which is a solid atom And because it's a noble gas, it's going to exist as XE two as as a atom. And so this is an atomic solid held by the week. Vander Wall's London dispersion force. And so therefore it should have a low melting point because this is a weak inter molecular force. So we can say overall that we would want to rule out the compounds that have the stronger molecular forces. So we would rule out our glucose molecule because it should have a high melting point. We also want to go ahead and rule out our silicon dioxide because even though it has the weak Van der Waals London dispersion force, it was a Covalin compound because it had these Covalin bonds and so that attributes more strength to this molecule, meaning it should have a higher melting point in comparison to xenon and our magnesium chlorine or chloride. And so we would rule this out because of the covalin bonds present in this molecule, which would increase its melting point. And so we want to go ahead and compare between our magnesium chloride which only had the electrostatic inter molecular force versus xenon which had the London dispersion inter molecular force. And we would say that the electrostatic inter molecular force is stronger than the Vander walls London dispersion force. And so because we know that the London dispersion forces weaker, we can say therefore sorry, we can say therefore Xenon. And let's make this need er we can say xenon will have the lowest boiling point as our final answer. So what's highlighted in yellow here is going to be our final answer to complete this example. So I hope that everything and sorry, this should say not boiling point but melting point. So now that that's fixed, this is our final answer. If you have any questions, please leave them down below. Otherwise I'll see everyone in the next practice video