Question
Read the passage given below and answer the following questions:
In ideally ionic structures, the coordination numbers of the ions are determined by electrostatic considerations. Cations surround themselves with as many anions as possible, and vice versa. This maximizes the attractions between neighbouring ions of opposite charge and hence maximizes the lattice energy of the crystal. This requirement led to the formulation of the radius ratio rule for ionic structures, in which the ions and the structure adopted for a particular compound depend on the relative sizes of the ions. Thus, for the stable ionic crystalline structures, there is definite radius ratio limit for a cation to fit perfectly in the lattice of anions, called radius ratio rule. This depends upon the ratio of radii of two types of ions $\frac{\text{r}_+}{r}$This ratio for coordination numbers $3, 4, 6$ and $8$ are respectively $0.155 - 0.225, 0.225 - 0.414, 0.414 - 0.732$ and $0.732 - 1.000$. The coordination number of ionic solids also depends upon temperature and pressure. On applying high pressure, coordination number increases. On the other hand, on applying high temperature, it decreases.
The following questions are multiple choice questions. Choose the most appropriate answer:
In ideally ionic structures, the coordination numbers of the ions are determined by electrostatic considerations. Cations surround themselves with as many anions as possible, and vice versa. This maximizes the attractions between neighbouring ions of opposite charge and hence maximizes the lattice energy of the crystal. This requirement led to the formulation of the radius ratio rule for ionic structures, in which the ions and the structure adopted for a particular compound depend on the relative sizes of the ions. Thus, for the stable ionic crystalline structures, there is definite radius ratio limit for a cation to fit perfectly in the lattice of anions, called radius ratio rule. This depends upon the ratio of radii of two types of ions $\frac{\text{r}_+}{r}$This ratio for coordination numbers $3, 4, 6$ and $8$ are respectively $0.155 - 0.225, 0.225 - 0.414, 0.414 - 0.732$ and $0.732 - 1.000$. The coordination number of ionic solids also depends upon temperature and pressure. On applying high pressure, coordination number increases. On the other hand, on applying high temperature, it decreases.
The following questions are multiple choice questions. Choose the most appropriate answer:
- The ionic radii of $K^+,Rb^+$ and $Br-$ are $137, 148$ and $195$pm. The coordination number of cation in RbBr and KBr structures are respectively.
- $8, 6$
- $6, 4$
- $6, 8$
- $4, 6$
- For a coordination number $4,$ the maximum limiting radius ratio is.
- $0.414$
- $0.732$
- $0.225$
- $0.155$
- If the radius of $Na^+$ ion is 95 pm and that of $Cl^-$ ion is $181$ pm, the coordination number of $Na^+$ ion is.
- $6$
- $4$
- $8$
- $12$
- Which is not the correct statement for ionic solids, in which positive and negative ions are held by strong electrostatic attractive forces?
- The radius ratio $\frac{\text{r}_+}{r}$ increases as coordination number increases.
- As the difference in size of ions increases, coordination number increases.
- When coordination number is eight, $\frac{\text{r}_+}{r}$ ratio lies between $0.225$ to $0.414.$
- In ionic solid of the type AX (ZnS, wurtzite), the coordination number of $Zn^2$ and $S^2$- respectively are $4 $and $4.$
- If the pressure of CsCl is increased, then its coordination number will.
- Increase
- Remain the same
- Decrease
- None of these.
