Question

Radius of the isoelectronic species:
A.Increases with increase of nuclear charge
B.Decreases with the increase of nuclear charge.
C.Is the same for all
D.First increases and then decreases

Answer 1

Hint: Try to recall that isoelectronic species are those having the same number of electrons. However they may differ in atomic number and hence differ in size. Now, by using this you can easily find the correct option from the given options.

Complete step by step solution:
-It is known to you that ions of different elements which have the same number of electrons differ in magnitude of nuclear charge.
-In a series of isoelectronic species, as the nuclear charge increases, the force of attraction by the nucleus on the electrons also increases. As a result of this, ionic radius decreases.
-In other words, we can say that the ionic radii of isoelectronic ions decrease with the increase in the magnitude of nuclear charge.
-The only deciding factor is the charge of the species. If the species is negatively charged, then it has more ionic radii and if it is positively charged then it has less ionic radii.
-Higher the magnitude of its negative charge the more will be its ionic radii and higher the magnitude of its positive charge the smaller will be its ionic radii.
Therefore, from above we can conclude that option B is the correct option to the given question.

Note: It should be remembered to you that ionic radii of elements tends to increase on going down the group on modern periodic table whereas it decreases on going along the period from left to right on modern periodic table.
Also, you should remember that the radius of an anion is always larger than that of its parent atom.