Question

what is the overall polarity of this molecule? h-c≡c-h polar nonpolar

Explanation:

• For a molecule to be polar, there must be a net dipole moment.
• In \(H - C\equiv C - H\) (acetylene), the \(C - H\) bonds have a small dipole (since \(C\) and \(H\) have slightly different electronegativities, \(C\approx2.5\), \(H\approx2.1\)).
• However, the molecule is linear (\(H - C\equiv C - H\) has a \(180^{\circ}\) bond angle). The dipole moments of the two \(C - H\) bonds are equal in magnitude and opposite in direction.
• When we vectorially add these dipole moments (\(\vec{\mu}_1\) and \(\vec{\mu}_2\) for the two \(C - H\) bonds), \(\vec{\mu}_{net}=\vec{\mu}_1+\vec{\mu}_2\). Since \(\vec{\mu}_1 =-\vec{\mu}_2\) (because of the linear geometry and symmetry), \(\vec{\mu}_{net} = 0\).

Answer:

nonpolar