Final answer:
The presence of double bonds in molecules like HNCO can affect bond angles and cause distortions in the usual tetrahedral angle of 109.5°.
Step-by-step explanation:
When there are double bonds, the bond angles can sometimes be affected. In the case of HNCO, the double bond between the carbon and nitrogen atoms can influence the bond angles. The double bond introduces more electron density, which can repel other electron pairs and cause a distortion in the bond angles.
For example, in HNCO, the carbon-nitrogen double bond can push the hydrogen atoms closer together, reducing the bond angle compared to what it would be in a structure without the double bond. This distortion can result in bond angles that are less than the usual tetrahedral angle of 109.5°.