Question

Among ${{H}_{2}},He_{2}^{+},L{{i}_{2}},B{{e}_{2}},{{B}_{2}},{{C}_{2}},{{N}_{2}},O_{2}^{-}$ and ${{F}_{2}}$, the number of diamagnetic species is (Atomic numbers:H=1,Li=3,Be=4,B=5,C=6,N=7,O=8,F=9).

Answer 1

Hint: Write the molecular orbital electronic configuration of all these compounds and those compounds which do not have any unpaired electrons in its last orbitals are considered as diamagnetic species.

Complete Step by Step Answer:
Diamagnetism is a quantum mechanical effect that occurs in all materials , when it is the only contribution to the magnetism , the material is called as diamagnetic materials. In this kind of magnetism characteristics of materials that line up at right angles to a non uniform magnetic field and that partly expel from their interior the magnetic field in which they are placed. The species in which no unpaired electrons are present are considered as diamagnetic species rest all are considered as paramagnetic species in which unpaired electrons are present. Here, the molecular orbital configuration of these species are :
${{H}_{2}}-{{\sigma }^{2}}_{1s}-Diamagnetic \\ He_{2}^{+}-\sigma _{1s}^{2}\sigma _{1s}^{*1}-Paramagnetic \\ L{{i}_{2}}-\sigma _{1s}^{2}\sigma _{1s}^{*1}\sigma _{2s}^{2}-Diamagnetic \\ B{{e}_{2}}-\sigma _{1s}^{2}\sigma _{1s}^{*1}\sigma _{2s}^{2}\sigma _{2s}^{*2}-Diamagnetic \\ {{B}_{2}}-\sigma _{1s}^{2}\sigma _{1s}^{*1}\sigma _{2s}^{2}\sigma _{2s}^{*2}\pi _{2{{p}_{y}}}^{1}\pi _{2{{p}_{z}}}^{1}-Paramagnetic \\ {{C}_{2}}-\sigma _{1s}^{2}\sigma _{1s}^{*1}\sigma _{2s}^{2}\sigma _{2s}^{*2}\pi _{2{{p}_{y}}}^{2}\pi _{2{{p}_{z}}}^{2}-Diamagnetic \\ {{N}_{2}}-\sigma _{1s}^{2}\sigma _{1s}^{*1}\sigma _{2s}^{2}\sigma _{2s}^{*2}\pi _{2{{p}_{y}}}^{2}\pi _{2{{p}_{z}}}^{2}\sigma _{2{{p}_{x}}}^{2}-Diamagnetic \\ O_{2}^{-}-\sigma _{1s}^{2}\sigma _{1s}^{*1}\sigma _{2s}^{2}\sigma _{2s}^{*2}\sigma _{2{{p}_{x}}}^{2}\pi _{2{{p}_{y}}}^{2}\pi _{2{{p}_{z}}}^{2}\pi _{2{{p}_{x}}}^{*2}\pi _{2{{p}_{y}}}^{*1}-Paramagnetic \\ {{F}_{2}}-\sigma _{1s}^{2}\sigma _{1s}^{*1}\sigma _{2s}^{2}\sigma _{2s}^{*2}\sigma _{2{{p}_{z}}}^{2}\pi _{2{{p}_{x}}}^{2}\pi _{2{{p}_{y}}}^{2}\pi _{2{{p}_{x}}}^{*2}\pi _{2{{p}_{y}}}^{*2}-Diamagnetic \\$
${{H}_{2}},He_{2}^{+},L{{i}_{2}},B{{e}_{2}},{{B}_{2}},{{C}_{2}},{{N}_{2}},O_{2}^{-}$

Among these electronic configurations , we can observe that those species in which the last electron remains unpaired that is it is not an even in number like 2, 4 etc. shows paramagnetic properties while those species in which the last orbital has even number of electron that is its paring is done and it exists there as a pair of electrons are called as diamagnetic species. When we count the number of paramagnetic species then we have 3 paramagnetic species and the rest 6 are considered as diamagnetic species .
Thus, the correct answer is 6 diamagnetic species.

Note: The charge denoted on the species given information about the loss or gain of electrons in the species . Like , the positive charge represents the loss of electrons while – charge represents the gain of electrons in the species. These electronic configurations should be written in accordance with the loss or gain of electrons to the neutral species .