Question 1

Which of the following molecules does NOT obey the octet rule?

Accepted Answer

In $BF3$, the central boron atom has only 6 valence electrons around it after sharing electrons with three fluorine atoms. Hence, it is an electron-deficient molecule and an exception to the octet rule.

Question 2

What is the shape of the $SF4$ molecule according to VSEPR theory?

Accepted Answer

$SF4$ has 4 bond pairs and 1 lone pair of electrons on the central sulfur atom. Its steric number is 5 ($sp^3d$ hybridization) giving it a see-saw shape.

Question 3

Which of the following molecules has a dipole moment equal to zero?

Accepted Answer

$BF3$ has a trigonal planar symmetrical geometry. The vector sum of the three bond dipoles cancels out, resulting in a net dipole moment of zero.

Question 4

What is the hybridization of the central phosphorus atom in $PCl5$?

Accepted Answer

In $PCl5$, phosphorus forms 5 sigma bonds using 5 valence electrons. Thus, it undergoes $sp^3d$ hybridization with a trigonal bipyramidal geometry.

Question 5

According to Molecular Orbital Theory (MOT), which of the following species is paramagnetic?

Accepted Answer

$O2$ has two unpaired electrons in its antibonding $\pi^ 2px$ and $\pi^ 2py$ molecular orbitals, making it paramagnetic.

Chemical Bonding and Molecular Structure