Copper iodide crystallizes in the zinc blende structure. The sep- aration between nearest neighbor cations and anions is approximately 311 pm, and the melting point is 606 °C. Potassium chloride, by contrast, crystallizes in the rock salt structure. Even though the separation between nearest-neighbor cations and anions is greater (319 pm), the melting point of potassium chlo- ride is higher (776 °C). Explain.

Video transcript

Hello, everyone in this video. We're using coordination numbers to explain why F E O has a higher melting point than ZN of S. So let's because some information here, let's recall that a higher coordination number leads to more contact between a carry on and an eye on display like this. So this is their relation and that would lead to a higher melting point. So this is how this coronation number relates to a melting point. Alright, so taking a look at our F E O. That's actually going to be a rock salt structure. And because of that and looking at the values given to you, either in your textbook or provided to you by your professor, we see that the coordination for that or any rock salt structure has a C N C coordination number of six. Now, taking a look at C and S. Again, looking at those values given to you, that's going to be a zinc blend. And if we follow the table then for the values given to you will see that the coordination for any of the sink blends is going to be for. So if we're comparing just the R six and R four, of course six has a higher coordination number following this because F E O has a higher coordination number. There's more contact between the captain and an ion and it has a higher melting point. So they formally answer this question, then F E O has a higher coordination number, therefore higher melting point. So M P. And this is going to be our final answer for this problem. Thank you all so much for watching.