Question

The atom having smallest size in the list below is

Na, Si, Cl, Ar

(A) Na

(B) Cl

(C) Si

(D) Ar

Answer 1

We know the modern periodic table is based on the properties of an element that are functions of their atomic number. The properties are based on the electronic configuration of the elements. Periodic properties are the trend in properties across a period from left to right to down the group. Some of the important periodic properties are metallic character, non-metallic character, atomic size, electron affinity, ionization potential and electronegativity.

Complete step by step answer:

We have to know that the atomic radius is an indication of the size of an atom.

As we go down a column of the periodic table, the atomic radii increase. This is because the outermost electron shell is getting larger and there is a larger principal quantum number, so the valence shell lies farther away from the nucleus. We can summarize this trend as follows,

As $\downarrow$ Periodic table, atomic radius $\uparrow$ .

As we go across a row on the periodic table, left to right, the atomic radius decreases. This is because the valence shell maintains the same principal quantum number, the number of protons, and so the nuclear charge increases as we go across the row. The increasing positive charge casts a tighter grip on the outermost electrons, so as we go across the periodic table, the atomic radii decrease. This could be summarized as follows,

As $\to$ Periodic table, atomic radius $\downarrow$ .

Sodium, silicon, chlorine, argon belong to the same period, and the period is 3.

As we move from left to right, the size of the atom decreases.

Halogen of any period is smallest in size. Hence size of $Cl$ will be small among all other elements.

So, the correct answer is Option (B).

Note:

We must remember that the ionization energy is the energy required to remove an electron from a gaseous atom (or) iron. The first ionization energy of an atom (or) molecule is the energy required to remove one mole of electrons from one mole of gaseous atoms (or) ions.

The ionization energy and the atomic size of an atom are inversely proportional which means that smaller the size of the higher the ionization energy.

$\text{Ionization energy} \,\propto \,\dfrac{1}{{\text{atomic size}}}$

Example: The atomic size of Nickel is ${\text{124pm}}$ and the atomic size of copper is ${\text{128pm}}$ as the size of the atom decreases ionization energy increases. Thus, nickel has higher ionization energy than copper.