b. If the coordination numbers for each of the two ions in a crystal lattice are
ID: 559227 • Letter: B
Question
b. If the coordination numbers for each of the two ions in a crystal lattice are identical, what must be true about the formula unit of the compound? c. An ionic compound forms between metal A and nonmetal B. The coordination number of the cation of element A is 4 and the coordination number of the anion of element B is 8. Write the chemical formula of the compound. 8. A general ionic bond forms between a cation X+ and an anion Y-. How will the strength of the ionic bond change if the following changes are made? In other words, will the resulting bond be stronger or weaker? a. The charge of the cation is doubled. b. The size of the cation is increased.Explanation / Answer
Part of the data is missing for the first problem; furnish the complete question. I shall answer question 8.
8a) A positively charged cation is held to a negatively charged anion by electrostatic forces of attraction in an ionic compound. If the charge of the anion and the size of the cation are kept constant, but the charge on the cation is increased, the ion pair will be bound together by stronger forces. This is due to the fact that for the same size of the cation, an increase in charge increases the charge density on the cation. The increased charge density draws the anion more strongly to the cation, thereby making the bond stronger.
8b) An increase in the size of the cation, the charge on the cation remaining constant, will lower the bond strength between the cation and the anion. This is due to decreased charge density on the cation. The charge density on an ion is defined as the charge on the ion divided by the size of the ion. Since the size increases, the charge density decreases and the cation can no longer pull the anion (the anion remains the same) toward itself. Therefore, the bond strength decreases.
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