Chapter 15, Problem 17TE

To determine

The reason for the large size of the beryllium atom than lithium atom.

Answer to Problem 17TE

The size of lithium atom is larger than the beryllium atom because of the nucleus energy of lithium atom is less than the beryllium atom.

Explanation of Solution

The atom's size is dependent on the number of protons in its nucleus, the number of electrons in its shell and the amount of energy hold by the atom.

Lithium and beryllium atoms present in the second period of the periodic table. The atomic number of lithium and beryllium is $3$ and $4$, respectively, so there are two electrons shells in both the atom. There is only $1$ electron is present in the outer shell of lithium, which is closely bonded with the nucleus, and there are $2$ electrons present in the outer shell of beryllium.

The nuclear charge of the lithium atom is less than the beryllium atom, so the electrons of beryllium are closely bonded with its nucleus. Therefore the size of the lithium atom is larger than the beryllium atom.

Conclusion:

Therefore, the size of lithium atom is larger than the beryllium atom because of the nucleus energy of lithium atom is less than the beryllium atom.