Chapter 15, Problem 4TC

To determine

Ranking of helium $\text{He}$, chlorine $\text{Cl}$, and argon $\text{Ar}$ atoms from greatest to smallest by atomic numbers.

Answer to Problem 4TC

The atomic number of helium is smallest then the atomic number of the chlorine and atomic number of the argon is largest, the correct order is $\text{He}<\text{Cl}<\text{Ar}$.

Explanation of Solution

The atomic number of an atom is same as the number of protons in the nucleus of that atom. The periodic table's atoms are ordered on the basis of an increase in the atomic number of atoms.

The helium atom's atomic number is $2$, the atomic number of the chlorine is $17$ and atomic number if argon is $18$.

The atomic number of the argon is largest, while the atomic number of helium is smallest. The atomic number of the chlorine lies between the helium and argon.

Conclusion:

Therefore, the atomic number of helium is smallest then the atomic number of the chlorine and atomic number of the argon is largest, the correct order is $\text{He}<\text{Cl}<\text{Ar}$.