Question

The p orbitals are aligned along the x, y and z axes as shown below.

If the orbitals overlap along z - axis, bonds formed by which of the following overlaps (if possible) is easiest to break?

• A. $p_x$ $-$ $p_x$
• B. $p_y$ $-$ $p_y$
• C. $p_z$ $-$ $p_z$
• D. $p_x$$-$ $p_z$

Answer 1

Answer: (A), (B)

The correct options are
A $p_x$ $-$ $p_x$
B $p_y$ $-$ $p_y$

In p-p overlap two kinds of overlap is possible:
(i) axial (end on end)
(ii) lateral (sideways)

If the orbitals overlap along x axis, then the two $p_z$ orbitals overlap axially. The sigma bond formed due to the axial overlap is stronger due to greater extent of overlap.


The $p_y$ and $p_x$ orbitals overlap laterally (sideways) with other $p_y$ and $p_x$ orbitals respectively. The pi bond formed due to sideways overlap of the orbitals is weaker than sigma bond because the extent of overlap is less than that of sigma bond.



The weaker bonds are easier to break. So, $p_y$ - $p_y$ and $p_x$ - $p_x$ overlaps are easier to break.

$p_x$ - $p_z$ overlap doesnot happen because for overlap to happen, the orbitals must have the same orientation i.e. lie along the same axis but $p_x$ and $p_z$ are perpendicular to each other.