Molecular Orbitals of Helium and Lithium

Q.

Question 19

Which of the following statement is not correct from the view point molecular orbital theory?

(a) $B{e}_2$ is not a stable molecule

(b) $H{e}_2$ is not stable but $H{e}_2^{+}$ is expected to exist.

(c) Bond strength of N_2 is maximum amongst the homonuclear diatomic molecules belonging to the second period.

(d) The order of energies of molecular orbitals in $N_2$ molecule is

$\sigma 2s<{\sigma }^{\ast }2s<\sigma 2p_z<({\pi }^{\ast }2p_x\simeq {\pi }^{\ast }2p_y)<{\sigma }^{\ast }2p_z$

Q. According to molecular orbital theory, which of the following is true with respect to ${{\mathrm{Li}}_2}^{+}\mathrm{and}{{\mathrm{Li}}_2}^{-}$ ?

1. Both are unstable
2. ${\mathrm{Li}}_2^{+}$ is unstable and
   ${\mathrm{Li}}_2^{-}$ is stable
3. ${\mathrm{Li}}_2^{+}$ is stable and
   ${\mathrm{Li}}_2^{-}$ is unstable
4. Both are stable

Q. In the following the correct bond order sequence is:

1. $O_2^{+}>O_2^{-}>O_2^{2-}>O_2$
2. $O_2^{+}>O_2>O_2^{-}>O_2^{2-}$
3. $O_2^{2-}>O_2^{+}>O_2^{-}>O_2$
4. $O_2>O_2^{-}>O_2^{2-}>O_2^{+}$

Q. $N_2$ and $O_2$ are converted into monocations, $N_2^{+}$ and $O_2^{+}$ respectively. which of the following statements is wrong ?

1. In $N_2$ the $N-N$ bond weakens
2. $N_2^{+}$ becomes diamagnetic
3. In $O_2,$ paramagnetism decreases
4. In $O_2,$ the $O-O$ bond order increases

Q. The correct electronic configuration for $H_2^{-}$ is:

1. $\sigma {1s}^2$
2. $\sigma \left({1s}^1\right){\sigma }^{\ast }({1s}^1$)
3. $\sigma \left({1s}^2\right){\sigma }^{\ast }\left(1s^1\right)$
4. $\sigma {1s}^3$

Q. If one of the electrons in the $H{e}_2$ molecule is taken to the next excited state, then the bond order in $H{e}_2$:

1. decreases by 1
2. increases by 0.5
3. increases by 1
4. no change

Q.

Give the trends in the following properties of Halogens- Electron affinity.

Q.

Draw the electronic distribution for silicon ($\mathrm{Z}=14$).

Q. The number of bonding electron pairs in $N_2$ on the basis of molecular orbital theory is:

Q. Four diatomic species are listed, identify the correct order in which the bond order is increasing in them.

1. $NO<O_2^{-}<C_2^{2-}<H{e}_2^{+}$

2. $O_2^{-}<NO<C_2^{2-}<H{e}_2^{+}$

3. $C_2^{2-}<H{e}_2^{+}<O_2^{-}<NO$

4. $H{e}_2^{+}<O_2^{-}<NO<C_2^{2-}$

Q. What is the bond order of $C{N}^{+}$?

Q.

Draw the electronic distribution for fluorine ($\mathrm{Z}=9$)

Q. If one of the electrons in the $B{e}_2$ molecule is taken to the next excited state, then the bond order in $B{e}_2$ is:

1. Increased by $1$
2. Decreased by $1$
3. Increased by $0.5$
4. Not changed

Q. Ground state electronic configuration of valence shell electrons in nitrogen molecule $\left(N_2\right)$ is written as $\left(S_{2s}{)}^2\right(S{\ast }_{2s}{)}^2\left(P_{2p}{)}^4\right(S_{2p}{)}^2$ Hence, the bond order of nitrogen molecule is:

1. $3$
2. $2$
3. $0$
4. $1$

Q.

Define octet rule. Write its significance and limitations.

Q. The correct electronic configuration for $H_2^{+}$ is:

1. $\sigma {1s}^1$
2. $\sigma \left({1s}^1\right){\sigma }^{\ast }({1s}^1$)
3. $\sigma \left({1s}^2\right){\sigma }^{\ast }\left(1s^1\right)$
4. $\sigma {1s}^2{\sigma }^{\ast }{1s}^2$

Q. Select the incorrect statement(s) about $N_2{F}_4$ and $N_2{H}_4$.
(i) In $N_2{F}_4$, d-orbitals are contracted by electronegative fluorine atoms, but d-orbital contraction is not possible by H-atoms in $N_2{H}_4$.
(ii) The $N-N$ bond energy in $N_2{F}_4$ is more than $N-N$ bond energy in $N_2{H}_4$.
(iii) The $N-N$ bond length in $N_2{F}_4$ is more than that in $N_2{H}_4$.
(iv) The $N-N$ bond length in $N_2{F}_4$ is less than that in $N_2{H}_4$.
Choose the correct code.

1. I, II and III
2. I and III
3. II and III
4. II and IV

Q. What is the bond-order of $C{N}^{-}$?

Q. What is the bond order of $N{O}^{+}$?

Q. Assertion :Electrons in $K$-shell revolve in circular orbit. Reason: Principal quantum number '$n$' is equal to $1$ for the electrons in $K$-shell.

1. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
3. Assertion is correct but Reason is incorrect
4. Assertion is incorrect but Reason is correct

Q. Which charge(s) on the $N_2$ molecule would give a bond order of $2.5$?

1. $+1$
2. $-1$
3. $+2$
4. $-2$

Q.

Using M.O. theory predict which of the following species has shortest bond length?

1. 

2. 

3. 

4. 

Q.

Using M.O. theory predict which of the following species has shortest bond length?

1. 

2. 

3. 

4. 

Q. The electronic configuration of gadolinium (At. no. $64$) is:

1. $\left[Xe\right]{4f}^8,{5d}^0,{6s}^2$
2. $\left[Xe\right]{4f}^7,{5d}^1,{6s}^2$
3. $\left[Xe\right]{4f}^3,{5d}^5,{6s}^2$
4. $\left[Xe\right]{4f}^6,{5d}^2,{6s}^2$

Q. When $N_2$ changes to $N_2^{+}$, the N - N bond distance increases and bond order decreases.
if true enter 1, else enter 0.

1. 1

Q. If one of the electrons in the $H{e}_2$ molecule is taken to the next excited state, then the bond order in $H{e}_2$:

1. increases by 1
2. decreases by 1
3. increases by 0.5
4. no change

Q. When $O_2$ changes to $O_2^{-}$ the O - O bond distance increases and bond order decreases.
If true enter 1, else enter 0.

1. 1

Q. The molecular electronic configuration of $H_2^{-}$ ion is:

1. $(\sigma 1s{)}^2$
2. $\left(\sigma 1s{)}^2\right({\sigma }^{\ast }1s{)}^2$
3. $\left(\sigma 1s{)}^2\right({\sigma }^{\ast }1s{)}^1$
4. $(\sigma 1s{)}^3$

Q. Number of lone pairs of electrons on $X$e atoms $Xe{F}_2,Xe{F}_4$ and $Xe{F}_6$ molecules are respectively.

1. 3, 2 and 1
2. 2, 3 and 1
3. 3, 2 and 0
4. 4, 3 and 2

Q. According to molecular orbital theory, which of the following is true with respect to ${{\mathrm{Li}}_2}^{+}\mathrm{and}{{\mathrm{Li}}_2}^{-}$ ?

1. Both are unstable
2. ${\mathrm{Li}}_2^{+}$ is unstable and
   ${\mathrm{Li}}_2^{-}$ is stable
3. ${\mathrm{Li}}_2^{+}$ is stable and
   ${\mathrm{Li}}_2^{-}$ is unstable
4. Both are stable