Question

Identify the wrong statement in the following.
A. Amongst isoelectronic species, the smaller the positive charge on the cation smaller is the ionic radius.
B. Amongst the isoelectronic species, greater the negative charge on the anion larger is the ionic radius.
C. Atomic radius of the elements increases as one moves down the first group of the periodic table.
D. Atomic radius of the elements decreases as one moves across left to right in the second period of the periodic table.

Answer 1

Here, we are given four different sentences with two concepts. The first concept is how the ionic radius changes in isoelectronic species and the second is how atomic radius changes in the periodic table. Therefore, for identifying the wrong sentence, we need to understand the facts regarding these two concepts.

Complete answer:
First, we will discuss the effect of the number of positive and negative charges on the ionic radius in isoelectronic species. It is observed that ionic radius is decreased with increasing positive charge and increased with increasing negative charge, and thus, anions are almost always larger than cations.From this, we can say that option A is the wrong statement and option B is the correct statement.

Now, we will discuss how the atomic radius changes in the periodic table. The number of energy levels increases as we move down a group as the number of electrons increases. Each subsequent energy level is further from the nucleus than the last. Therefore, the atomic radius increases as the group and energy levels increase.

Whereas, as we go across a period, electrons are added to the same energy level. At the same time, protons are being added to the nucleus. The concentration of more protons in the nucleus creates a decrease in atomic radius.From this, we can say that both the statements C and D are correct statements.

Hence, option A is the right answer.

Note: It is important to note that anions or negative ions are larger than their respective atoms because electron-electron repulsion forces them to spread further apart. However, cations or positive ions are smaller than their respective atoms because there are less electron-electron repulsions due to which they can come closer together.