Chemical Bonding and Molecular Structure - NEET Review

Flashcards testing concepts of Chemical Bonding and Molecular Structure based on NEET chapterwise practice material.

What type of compound is formed when a cation and an anion combine in a crystal lattice?

An ionic compound, which is held together by electrostatic forces of attraction.

Why does the $\text{H}_2\text{O}$ molecule contain no $\pi$-bonds?

Because the hydrogen atom lacks vacant orbitals required for $\pi$-bond formation.

Why does $\text{BeF}_2$ have a net dipole moment of zero, whereas $\text{H}_2\text{O}$ is dipolar?

$\text{BeF}_2$ is a linear molecule with a $180^\circ$ bond angle where bond polarities cancel out, whereas $\text{H}_2\text{O}$ has an angular/bent geometry with a $104.5^\circ$ bond angle.

What are the number of bond pairs and lone pairs on the central nitrogen atom in a $\text{NO}_3^-$ ion?

4 bond pairs and 0 lone pairs.

What is the correct order of decreasing bond enthalpy for methyl halides ($\text{CH}_3\text{-X}$)?

$$\text{CH}_3\text{-F} > \text{CH}_3\text{-Cl} > \text{CH}_3\text{-Br} > \text{CH}_3\text{-I}$$

According to Fajan's rule, what is the sequence of increasing covalent character among $\text{NaCl}$, $\text{LiCl}$, and $\text{BeCl}_2$?

$$\text{NaCl} < \text{LiCl} < \text{BeCl}_2$$

What is the formal charge on each oxygen atom and the $\text{P-O}$ bond order in a $\text{PO}_4^{3-}$ ion?

The formal charge on each oxygen atom is $-0.75$ and the $\text{P-O}$ bond order is $1.25$.

What is the correct order of electron pair repulsion strength according to VSEPR theory?

lone pair-lone pair > lone pair-bond pair > bond pair-bond pair

How many $\sigma$ and $\pi$ bonds are present in a molecule of ethene ($\text{C}_2\text{H}_4$)?

5 $\sigma$ bonds and 1 $\pi$ bond.

What is the hybridisation of boron and the number of electrons around it in $\text{BF}_3$?

Boron undergoes $sp^2$ hybridisation and has 6 electrons around it.

What type of hybridisation is adopted by each boron atom in diborane ($\text{B}_2\text{H}_6$)?

$sp^3$ hybridisation.

What is the correct sequence of molecular orbital energies for the $\text{N}_2$ molecule?

$$\sigma 1s < \sigma^* 1s < \sigma 2s < \sigma^* 2s < (\pi 2p_x = \pi 2p_y) < \sigma 2p_z < (\pi^* 2p_x = \pi^* 2p_y) < \sigma^* 2p_z$$

According to molecular orbital theory, why does a diatomic helium molecule ($\text{He}_2$) not exist?

Because its bond order is zero ($\text{BO} = \frac{2 - 2}{2} = 0$).

According to molecular orbital theory, what types of bonds make up the double bond in a $\text{C}_2$ molecule?

Both bonds in the double bond of $\text{C}_2$ are $\pi$-bonds because the four valence electrons occupy two degenerate $\pi$-molecular orbitals.

Why is the boiling point of p-nitrophenol higher than that of o-nitrophenol?

Because p-nitrophenol exhibits intermolecular hydrogen bonding, whereas o-nitrophenol exhibits intramolecular hydrogen bonding.

Which oxygen species among $\text{O}_2^+$, $\text{O}_2$, $\text{O}_2^-$, and $\text{O}_2^{2-}$ has the minimum bond length?

$\text{O}_2^+$ has the minimum bond length because it has the highest bond order ($2.5$).