World 1 · Atoms & Bonds · 8 minLone pairs bend the shape
Electron-domain geometry vs molecular shape
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Lone pairs are electron domains too, so they help set the arrangement. But a molecular shape is named only from where the atoms are. With four domains and one lone pair, the domains still form a tetrahedron, but atoms sit at only three of its four corners.
To count lone pairs on the central atom, take its valence electrons, subtract the electrons it puts into bonds (one per single bond), and halve what is left. Nitrogen has 5 valence electrons; oxygen has 6.
Check yourself
The H–N–H angle in NH₃ is about 107°, a little less than the ideal tetrahedral angle of 109.5°. Why?
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