What is the radious of anion of nacl if it's radious of captions is r
Answers
Answer:
Explanation:
The electrostatic interaction between charged spheres is responsible for the formation of bonding in an ionic model. The determination of the sizes of the ionic radius is possible by the internuclear separation of the separate contributions of the anion from cation.
The radius of one ion is calculated on the basis of a standard ion (by assuming the value of one ion). The standard ion is oxide ion which helps in the determination of the other ions. This is because an oxide ion occurs in combination with many different elements. Moreover, an oxide ion is comparatively unpolarizable. Therefore, the significant change in the size is negligible on the basis of the counterion present.
Ionic radius is helpful in the prediction of crystal structures including lengths of the axes, lattice parameters, etc. However, this prediction is possible provided the values of the radius of the ions are taken from the same origin or same reference ion. This is important for achieving the correct relative sizes.
It is essential to understand that ionic radius differs on the basis of coordination number. The increase in coordination number results in the ions moving further away from the central ion to fit more ions. Therefore, increase in coordination number will increase the interionic separation and decrease the short ranged repulsion. This, in turn, will allow the electrons present on the central ion to expand thereby increasing the size of the central ion.
Therefore, we can conclude that ionic radius will increase with an increase in coordination number. The sizes of ions help in the prediction of the structure which will form during the combination of ions. The prediction is of the ions in the structure is done by Radius Ratio or Radius Ration rule. How? Let us understand!
Browse more Topics under The Solid State
General Introduction
Crystalline and Amorphous Solids
Space Lattice or Crystal Lattice and Unit Cell
Number of Particles in Unit Cells
Close Packing in Crystals
Tetrahedral and Octahedral Voids
Density of a Cubic Crystal
Imperfections or Defects in a Solid
Electrical Properties of Solids
Magnetic Properties of Solids
The Radius Ratio Rule
If we consider an array of anions present in the form of cubic close packing, the tetrahedral holes and the octahedral holes will vary in the sizes. Therefore, the cations will occupy the voids only if they are enough space to accommodate them. This prediction of whether the ions will be able to hold the cations can be done on the basis of Radius Ratio.
Ionic Crystals comprises many cations and anions. We know that anions are larger in size and surround the smaller cations. They are arranged in space such that anions and cations touch each other and produce maximum stability.
This stability of the ionic crystals can be explained on the basis of radius ratio. Therefore, radius ratio is the ratio of cation to the ratio of an anion. Here, Ratio of cation= r, Ratio of anion = R. Thus, Radius ratio = (r/R). Limiting radius ratio helps in expressing the range of radius ratio.
Solved Example for You
Question: If a solid “A+B–” has a structure similar to NaCl. Consider the radius of anion as 250 pm. Find the ideal radius of the cation in the structure. Is it possible to fit a cation C+ of radius 180 pm in the tetrahedral site of the structure “A+B–”? Explain your answer
Solution: If the A+B– structure is similar to Na+Cl– ion then we know that six Cl– ions will surround Na+ and vice versa. Therefore, Na+ ion fits into the octahedral void. Therefore the limiting ratio for an octahedral site is 0.414
Thus, limiting radius ratio= r/R= 0.414
From the question, R=250 pm
Therefore, r=0.414R= 0.414 × 250pm
Hence, r= 103.5pm
So the ideal radius ration of cation will be 103.5pm or A+ = 103.5 pm
From the above table, we know r/R for a tetrahedral site is 0.225
Therefore, r/R= 0.225
Or, r= 0.225R = 0.225 × 250pm = 56.25 pm
Thus, the ideal radius for the cation in the given structure will be 56.25 pm for a tetrahedral site. However, we know the radius of C+ is 180 pm. This means that the radius of C+ is much larger than 56.25 pm. Therefore, it is not possible to fit cation C+ in a tetrahedral site.
Radius Ratio Rule
Below Table demonstrates the relationship between radius ratio (limiting ratio) and coordination number.
