Chemical Bonding & Molecular Structure
In hydrogen azide (above) the bond orders of bond (I) and (II) are :
(Atomic nos : B = 5, S = 16, Ni = 28, Xe = 54)
Total number of non-bonded electrons present in NO2$-$ ion based on Lewis theory is ______.
Explanation:
NO$_2^-$ ion

Structure (Lewis Structure)
Nitrogen (N) has 2 non-bonding electrons. The total valence electrons of N is 5. Out of 5, 3 electrons are bonding electrons and 2 electrons are non-bonding electrons.
Double bonded oxygen has 4 non-bonding electrons. Oxygen valence electrons : 6
Out of 6, 2 are bonding electrons are 4 are non-bonding electrons.
Negatively charged oxygen has 6 non-bonding electrons. The negative charge is due to the extra electron present. So, the total number of non-bonded electrons present in NO$_2^-$ ion based on Lewis theory is
$2(of\,N) + 4(of\,O) + 6(of\,{O^ - })$
$ = 2 + 4 + 6 = 12$
The number of molecules/ions that show linear geometry among the following is __________.
$\mathrm{SO}_2, \mathrm{BeCl}_2, \mathrm{CO}_2, \mathrm{~N}_3^{-}, \mathrm{NO}_2, \mathrm{~F}_2 \mathrm{O}, \mathrm{XeF}_2, \mathrm{NO}_2^{+}, \mathrm{I}_3^{-}, \mathrm{O}_3$
Explanation:
Linear species are
Total number of electrons present in $\left(\pi^*\right)$ molecular orbitals of $\mathrm{O}_2, \mathrm{O}_2^{+}$ and $\mathrm{O}_2^{-}$ is ________.
Explanation:
$\begin{aligned} & \mathrm{O}_2(16 \mathrm{e}):\left(\sigma_{1 \mathrm{~s}}\right)^2\left(\sigma_{1 \mathrm{~s}}^*\right)^2\left(\sigma_{2 \mathrm{~s}}\right)^2\left(\sigma_{2 \mathrm{~s}}^*\right)^2 \\ & \left(\sigma_{2 \mathrm{p}}\right)^2\left[\left(\pi_{2 \mathrm{p}}\right)^2=\left(\pi_{2 \mathrm{p}}\right)^2\right],\left[\left(\pi_{2 \mathrm{p}}^*\right)^1=\left(\pi_{2 \mathrm{p}}^*\right)^1\right] \end{aligned}$
Number of $\mathrm{e}^{-}$ present in $\left(\pi^*\right)$ of $\mathrm{O}_2=2$
Number of $\mathrm{e}^{-}$ present in $\left(\pi^*\right)$ of $\mathrm{O}_2^{+}=1$
Number of $\mathrm{e}^{-}$ present in $\left(\pi^*\right)$ of $\mathrm{O}_2^{-}=3$So total $\mathrm{e}^{-}$ in $\left(\pi^*\right)=2+1+3=6$
The total number of species from the following in which one unpaired electron is present, is _______.
$\mathrm{N}_2, \mathrm{O}_2, \mathrm{C}_2^{-}, \mathrm{O}_2^{-}, \mathrm{O}_2^{2-}, \mathrm{H}_2^{+}, \mathrm{CN}^{-}, \mathrm{He}_2^{+}$
Explanation:
| Species | Unpaired e |
|---|---|
| $ \mathrm{N}_2 $ |
0 |
| $ \mathrm{O}_2 $ |
2 |
| $ \mathrm{C}_2^{-} $ |
1 |
| $ \mathrm{O}_2^{-} $ |
1 |
| $ \mathrm{O}_2^{2-} $ |
0 |
| $ \mathrm{H}_2^{+} $ |
1 |
| $ \mathrm{CN}^{-} $ |
0 |
| $ \mathrm{He}_2^{+} $ |
1 |
Number of molecules having bond order 2 from the following molecules is _________.
$\mathrm{C}_2, \mathrm{O}_2, \mathrm{Be}_2, \mathrm{Li}_2, \mathrm{Ne}_2, \mathrm{~N}_2, \mathrm{He}_2$
Explanation:
To determine the number of molecules with a bond order of 2 from the given molecules, we need to first calculate the bond order for each molecule. The bond order can be determined using Molecular Orbital Theory (MOT). The bond order is given by the formula:
$\text{Bond Order} = \frac{\text{Number of bonding electrons} - \text{Number of anti-bonding electrons}}{2}$
Let's evaluate each molecule individually:
1. $\mathrm{C}_2$:
For $\mathrm{C}_2$, the total number of electrons is 12. The molecular orbital configuration will be $\left( \sigma_{1s} \right)^2 \left( \sigma_{1s}^* \right)^2 \left( \sigma_{2s} \right)^2 \left( \sigma_{2s}^* \right)^2 \left( \pi_{2p_x} \right)^2 \left( \pi_{2p_y} \right)^2$. There are 8 bonding electrons and 4 anti-bonding electrons:
$\text{Bond Order} = \frac{8 - 4}{2} = 2$
2. $\mathrm{O}_2$:
For $\mathrm{O}_2$, the total number of electrons is 16. The molecular orbital configuration will be $\left( \sigma_{1s} \right)^2 \left( \sigma_{1s}^* \right)^2 \left( \sigma_{2s} \right)^2 \left( \sigma_{2s}^* \right)^2 \left( \sigma_{2p_z} \right)^2 \left( \pi_{2p_x} \right)^2 \left( \pi_{2p_y} \right)^2 \left( \pi_{2p_x}^* \right)^1 \left( \pi_{2p_y}^* \right)^1$. There are 10 bonding electrons and 6 anti-bonding electrons:
$\text{Bond Order} = \frac{10 - 6}{2} = 2$
3. $\mathrm{Be}_2$:
For $\mathrm{Be}_2$, the total number of electrons is 8. The molecular orbital configuration will be $\left( \sigma_{1s} \right)^2 \left( \sigma_{1s}^* \right)^2 \left( \sigma_{2s} \right)^2 \left( \sigma_{2s}^* \right)^2$. There are 4 bonding electrons and 4 anti-bonding electrons:
$\text{Bond Order} = \frac{4 - 4}{2} = 0$
4. $\mathrm{Li}_2$:
For $\mathrm{Li}_2$, the total number of electrons is 6. The molecular orbital configuration will be $\left( \sigma_{1s} \right)^2 \left( \sigma_{1s}^* \right)^2 \left( \sigma_{2s} \right)^2$. There are 4 bonding electrons and 2 anti-bonding electrons:
$\text{Bond Order} = \frac{4 - 2}{2} = 1$
5. $\mathrm{Ne}_2$:
For $\mathrm{Ne}_2$, the total number of electrons is 20. The molecular orbital configuration will be $\left( \sigma_{1s} \right)^2 \left( \sigma_{1s}^* \right)^2 \left( \sigma_{2s} \right)^2 \left( \sigma_{2s}^* \right)^2 \left( \sigma_{2p_z} \right)^2 \left( \pi_{2p_x} \right)^2 \left( \pi_{2p_y} \right)^2 \left( \pi_{2p_x}^* \right)^2 \left( \pi_{2p_y}^* \right)^2 \left( \sigma_{2p_z}^* \right)^2$. There are 10 bonding electrons and 10 anti-bonding electrons:
$\text{Bond Order} = \frac{10 - 10}{2} = 0$
6. $\mathrm{N}_2$:
For $\mathrm{N}_2$, the total number of electrons is 14. The molecular orbital configuration will be $\left( \sigma_{1s} \right)^2 \left( \sigma_{1s}^* \right)^2 \left( \sigma_{2s} \right)^2 \left( \sigma_{2s}^* \right)^2 \left( \sigma_{2p_z} \right)^2 \left( \pi_{2p_x} \right)^2 \left( \pi_{2p_y} \right)^2$. There are 10 bonding electrons and 4 anti-bonding electrons:
$\text{Bond Order} = \frac{10 - 4}{2} = 3$
7. $\mathrm{He}_2$:
For $\mathrm{He}_2$, the total number of electrons is 4. The molecular orbital configuration will be $\left( \sigma_{1s} \right)^2 \left( \sigma_{1s}^* \right)^2$. There are 2 bonding electrons and 2 anti-bonding electrons:
$\text{Bond Order} = \frac{2 - 2}{2} = 0$
Thus, the molecules with a bond order of 2 from the given list are $\mathrm{C}_2$ and $\mathrm{O}_2$. Therefore, the number of molecules having bond order 2 is 2.
Number of molecules from the following which are exceptions to octet rule is _________.
$\mathrm{CO}_2, \mathrm{NO}_2, \mathrm{H}_2 \mathrm{SO}_4, \mathrm{BF}_3, \mathrm{CH}_4, \mathrm{SiF}_4, \mathrm{ClO}_2, \mathrm{PCl}_5, \mathrm{BeF}_2, \mathrm{C}_2 \mathrm{H}_6, \mathrm{CHCl}_3, \mathrm{CBr}_4$
Explanation:
$\mathrm{NO}_2, \mathrm{H}_2 \mathrm{SO}_4, \mathrm{BF}_3, \mathrm{ClO}_2, \mathrm{PCl}_5, \mathrm{BeF}_2$
These are exception of octet rule






