Question

For which of the following species, Bohr theory does not apply?
A.${{\text{H}}^ - }$
B.H
C.${\text{H}}{{\text{e}}^ + }$
D.${\text{L}}{{\text{i}}^{{\text{2 + }}}}$

Answer 1

Hint:We know that Bohr proposed the model of atoms on the basis of Planck’s quantum theory. This theory was primarily applicable to the hydrogen atom and one electron species.

Complete step by step answer:
Here, we have to count the number of electrons in all the given species.
Option A is ${{\text{H}}^ - }$. The negative sign indicates that one electron is gained. So, the total number of electrons of ${{\text{H}}^ - }$ is two. We know that Bohr Theory is applicable to only one electron species. So, The Bohr theory is not applied to ${{\text{H}}^ - }$.
Option B is H. We know that the Bohr theory is applicable to hydrogen atoms.
Option C is ${\text{H}}{{\text{e}}^ + }$. The positive sign indicates that one electron is less than He. So, ${\text{H}}{{\text{e}}^ + }$ is a one electron species. So, The Bohr Theory is applicable to ${\text{H}}{{\text{e}}^ + }$.
Option D is ${\text{L}}{{\text{i}}^{{\text{2 + }}}}$. We know that the atomic number of lithium is 3. The +2 sign indicates that the two electrons is less in ${\text{L}}{{\text{i}}^{{\text{2 + }}}}$ than Li, that means, ${\text{L}}{{\text{i}}^{{\text{2 + }}}}$
is a one electron species. So, The Bohr Theory is applicable to ${\text{H}}{{\text{e}}^ + }$.
Hence, the correct answer is option A.

Note:
The main postulates of Bohr’s theory are as follows:
1) In a hydrogen atom, the electron revolves around the nucleus in a well defined circular path of fixed radius and energy.
2) The energy of an electron in its orbit does not change of its own with time.
3) Electrons when received a required amount of energy jumps to a higher stationary state.