Chapter 15, Problem 2TC

To determine

The rank from the smallest to greatest in order of atomic size of the atoms: potassium K, sodium Na, and lithium Li.

Answer to Problem 2TC

Lithium is arranged at first, then sodium and potassium in ascending order of their atomic mass $Li<Na<K.$

Explanation of Solution

The atomic size of the atom depends on the number of electrons in the atoms that fill the shells of atoms. The more the number of electrons more will be the shell filled by the electrons of the atoms.

Potassium (K), sodium (Na), and Lithium (Li) are the elements of first group in the periodic table.

The atomic number of these elements is as follows:

Elements	Atomic number
Lithium (Li)	3
Sodium (Na)	11
Potassium (K)	19

From the above table, the atomic number of lithium is the least of the given elements, then sodium has more atomic number than lithium and the potassium has the highest atomic number. As the atomic size depends on the atomic number of the elements, so lithium is arranged as first, then sodium and the potassium in the last in the smallest to greatest order of their atomic mass.

Conclusion:

Therefore, lithium is arranged at first, then sodium and potassium in ascending order of their atomic mass $Li<Na<K.$