Question

Which one of the following is smallest in size?
A. ${N^{ - 3}}$
B. ${O^{ - 2}}$
C. ${F^ - }$
D. $N{a^ + }$

Answer 1

Hint: In order to answer the question, first we have to check the periodic table and the properties on which the elements are arranged. And, then understand the logic of charges on the elements like positive or negative.

Complete answer:
As we go across the period, the size of the atom decreases. So, the size of Sodium is less compared to Nitrogen, Oxygen and Fluorine. Also, the size of cation is always less than that of an atom. So, $N{a^ + }$ has the smallest size.
The size of any element depends on the atomic radius of the element. And, the periodic table is arranged also according to the atomic radius of the elements. As we move down an element group (column), the size of atoms increases. This is because each atom further down the column has more protons and neutrons and also gains an additional electron energy shell. And, as we move across an element period (row), the overall size of atoms decreases slightly. Even though atoms further to the right have more protons, neutrons, and electrons, the outer electron shell is the same. The increased number of protons exerts a stronger positive charge, pulling the electrons in toward the nucleus.
And, now a question is arising here that why positive charge on an element is smaller than the negative charge on an element. So, positive charge on an element is the cation on the element or we can say that Cation is formed when we remove one electron from an atom. On the other hand, a negative charge on an element is the anion on the element or we can say that Anion is formed when we add one electron to an atom. So after removing an electron the size of the atom decreases and by adding an electron the size increases. That’s why Positive Charge on the element is smaller than Negative Charge on the element.
Hence, the correct option is, ‘(D) $N{a^ + }$’.

Note: Normally, when getting left to directly across the periodic table, there is a pattern of decreasing atomic radius. Be that as it may, in the transition metals, moving left to right, there is a pattern of expanding atomic radius which levels off and gets steady. In the changed components, the quantity of electrons is expanding however with a certain goal in mind. The quantity of electrons increment going across a period, hence, there is more draw of these electrons towards the nucleus.