Question

Although both \(CO_2\) and \(H_2O\) are triatomic molecules, the shape of \(H_2O\) molecule is bent while that of \(CO_2\) is linear. Explain this on the basis of dipole moment.

Answer 1

Concept Used:

Molecular shape is influenced by bond polarity and the resultant dipole moment of the molecule.

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Explanation:

In the CO₂ molecule, the two C=O bonds are polar, but the molecule has a linear geometry with a bond angle of 180°.

The dipole moments of the two C=O bonds are equal in magnitude and act in opposite directions.

As a result, the bond dipoles cancel each other completely, giving CO₂ a zero dipole moment.

This symmetrical distribution of charge makes the CO₂ molecule linear.

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In contrast, in the H₂O molecule, the O–H bonds are polar and the molecule has a bent (V-shaped) geometry with a bond angle of about 104.5°.

Because of this angular structure, the dipole moments of the two O–H bonds do not cancel each other.

Hence, H₂O has a net dipole moment.

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Conclusion:

The presence of a net dipole moment in H₂O leads to a bent shape, whereas cancellation of dipole moments in CO₂ results in a linear structure.

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Final Answer:

CO₂ is linear due to zero dipole moment, while H₂O is bent because it possesses a net dipole moment.