Identify the bond angle and molecular shape of H2O.

Question

BlackTom AI · Accepted Answer

We start by restating the problem in our own words to ensure understanding: identify both the bond angle and the molecular shape for H2O.
Option 1 says: bond angle ≈ 90°, shape = trigonal pyramid. This is inconsistent with water’s actual geometry: trigonal pyramidal shapes occur in molecules like NH3, not H2O, and a 90° angle is not associated with water's geometry. The bent shape is the key feature for H2O, not trigonal pyramidal.
Option 2 states: bond angle ≈ 120°, shape = trigonal planar. A 120° angle and trigonal planar geometry would correspond to sp2-hybridized centers with no lone pairs affecting the geometry, which does not describe water, where lone pairs push the hydrogens downward and cause a bent shape; thus this is incorrect.
Option 3 presents: bond angle ≈ 109.5°, shape = bent. The bent shape matches water due to the two lone pairs on oxygen causing repulsion that reduces the H–O–H angle from the ideal tetrahedral 109.5° to a smaller value; however, the commonly cited experimental value is about 104.5°. In many introductory treatments, 109.5° is associated with a tetrahedral arrangement, and the bent shape arises from the same electron-pair geometry. Thus option 3 captures the correct combination of shape and a rounded, tetrahedral-influenced angle, aligning with the idea that water’s electron pair geometry is tetrahedral, even if the exact observed angle is slightly different.
Option 4 asserts: bond angle ≈ 90°, shape = bent. Although ‘bent’ is the correct shape descriptor for H2O, a 90° bond angle is characteristic of a very different geometry (e.g., a square planar or certain d-orbital interactions) and does not describe water’s actual angle; therefore this option is not accurate.
To summarize the mismatches: options 1 and 4 both misstate the angle for a bent molecule like water; option 2 misstates both the angle and the geometry; option 3 correctly identifies bent geometry and gives a plausible bond angle consistent with a tetrahedral electron-pair framework, even if the precise measured value is slightly different in practice. The key ideas are that water has a bent shape due to two lone pairs on oxygen and that the idealized electron-pair geometry is tetrahedral, which is associated with an angle near 109.5°, rather than 90° or 120°.

Identify the bond angle and molecular shape of H2O.单项选择题

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