Look at the location of elements A, B, C, and D in the following periodic table:

(e) Which of these oxides has the highest melting point? Which has the lowest melting point?

Video transcript

All right. Hello everyone. So this question is asking us to consider the positions of the following elements in the periodic table, determine the element that would form the oxide with the highest melting point and the lowest melting point. So first let me go ahead and scroll down to open up some space towards the bottom of the screen. Recall that the location of a of an element in the periodic table is going to determine its highest oxidation state. And therefore the formula of its oxide starting off with element A towards the left side, it is in group two a of the periodic table and it is in period three. In other words, row three, this means that element A is going to be magnesium and magnesium has a highest oxidation state of positive two. So we can combine this now with oxygen which is going to have a negative or rather an oxidation state of negative two when it is an oxide. So in order to determine the chemical formula of the resulting oxide, based on this information, recall that we're going to have to crisscross the charges. So the charge of one element becomes the subscript on the other element. But regardless, here we end up with a formula of MG 202 which simplifies to simply MGO. So the formula for an oxide using magnesium is going to be MGO. Now keep in mind though that elements in group two A form oxides with oxygen gas except for burial. If this element was barium, then you would form a peroxide instead. But with this in mind, let's go ahead and talk about element B. Now, element B is in group three A and it's in period four. So B is going to be galleon and gallium is going to have a highest oxidation state of positive three. So once again, we can crisscross these charges and obtain a molecular formula of G A 203. In this case, we cannot simplify these subscripts any further. So they are going to stay as its. Now lets talk about element C. Element C is in group four A period two, which means that P element C here is none other than carbon, carbon has a highest oxidation state of positive four and oxygens still negative too. So when we crisscross these charges, we get C 204 which simply simplifies the co two. And last but not least is element D here which is in group five A period three. So element T is phosphorus, phosphorus has a highest oxidation state of positive five. So when crisscrossing the charges the molecular formula of the oxide with phosphorus is going to be P 205. So for the sake of visibility, I'm going to go ahead and write all of these oxides in a list. We have MGO G A 203 CO2 and P 205. So now when deciding which of these four oxides has the highest and the lowest boiling point, it is a question of comparing the intermolecular forces or the IMF s that these compounds exhibit recall that intermolecular forces are attractive forces that keep molecules atoms etc close together. The stronger the intermolecular force, the more energy is required to break them during a phase transition. Hence why the melting or the boiling point gets higher. Now, first and foremost, we can recall the fact that ionic bonds are stronger than covalent bonds. So because of that ionic compounds are going to have higher boiling or melting points than covalent compounds. An ionic compound is a chemical compound created by combining a metal with a non metal. Oxygen is a non metal and notably magnesium and gallium are both metals. So the first two oxides on our list here, MGO and G A 203 are examples of ionic compounds. By contrast, carbon and phosphorus are nonmetals. So the last two oxides are covalent compounds. So now, in order to decide which of the two ionic compounds is going to have the higher melting point, we have to consider the difference in electron negativity between each other. Recall that the greater the electron negativity difference, the more ionic that compound is going to be. Now, with that in mind, recall that electron negativity can be predicted using the periodic table. So let's go ahead and scroll up for a second magnesium which is element A here is much farther away than gallium specifically, much farther to the left. And recall that electron negativity increases as you go to the right and upwards in the periodic table. So because magnesium is farther away from oxygen, that's on the right side of the periodic table. The electronegativity difference between these two atoms is going to be much greater because recall that oxygen is in group six A and period two. So gallium being closer to oxygen in the periodic table is going to have less of an electron negativity difference compared to magnesium and oxygen. So because of this MGO is more ionic than G A 203, which means that the highest melting point is going to be the oxide that contains magnesium, right. MGO is going to have the highest melting point of the compounds listed here. So now let's talk about our two covalent compounds co two and P 205 recall that there is an electron negativity difference between carbon and oxygen. However, there is also a symmetry to the structure of carbon dioxide. So while there is a dipole moment going towards oxygen, those dipole moments actually cancel out which makes carbon dioxide a nonpolar covalent compound. And because it's a nonpolar covalent compound, it's going to exhibit London dispersion forces which are the weakest type of IMF now P 205. On the other hand does exhibit dipole moments as well because there is a difference in electronegativity between phosphorus and oxygen, but those do not cancel out. So P 205 is a pulver covalent compound which is going to exhibit dile dile interactions that are stronger than dispersion forces. So, because co two has the weakest IMF s here, given the fact that it's a nonpolar covalent compound, it is going to have the lowest melting point. So therefore, the oxide with carbon is going to have the lowest melting point and there you have it. So here an oxide with element A magnesium is going to have the highest melting point and the oxide with carbon or element C is going to have the lowest melting point and there you have it. So if you watch this video all the way through, thank you so very much for doing so. And I hope you found this helpful.