Lone pairs repel more strongly than bonding pairs, compressing angles such as 104.5 degrees in water.
Practise Bonding & Molecular Structure All Bonding & Molecular Structure topics
Real bond angles often differ from the ideal values predicted by VSEPR because repulsions between electron groups are not all equal. The order of repulsion is lone pair-lone pair greater than lone pair-bonding pair greater than bonding pair-bonding pair, so lone pairs compress the bond angles around them. Multiple bonds occupy more space than single bonds, which further distorts the angles. Going down a group, bond angles usually shrink as the central atom becomes larger. These deviations are essential for predicting angles accurately.
Key ideas: Apply the repulsion order and rank angles in a series: CH4 109.5, NH3 107, H2O 104.5. Larger lone pair effects on small central atoms with electronegative substituents: ammonia has greater angle than NF3 because the electronegative F draws bonding electrons away, making bond pairs occupy less space. Double bonds compress adjacent single-bond angles, as in 116 degrees for H-C-H in H2CO.
Common mistakes and connections: Common mistakes are assuming ideal angles, ignoring substituent electronegativity (PF3 versus PH3 trend), and applying the rule backwards for central atoms in lower periods. Also the angle in H2S is 92 and not 104. Links to Bent's rule, hybridization, VSEPR repulsion ranking and electronegativity.
Down group 16 the H-X-H angle falls from 104.5 to about 90 degrees as central atoms get larger and use nearly pure p orbitals for bonding. The interactive lesson shows this as a live animation or chart.
Methane has an angle of 109.5 degrees, ammonia 107 degrees and water 104.5 degrees, as lone pairs are added to the central atom.
Lone pairs repel more strongly than bonding pairs, compressing angles such as 104.5 degrees in water.
Bond Angle Deviations is a intermediate topic in Bonding & Molecular Structure. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Bonding & Molecular Structure first: T-Shaped Geometry, Square Planar Geometry, Square Pyramidal Geometry.
The next topics in Bonding & Molecular Structure are Valence Bond Theory and Sigma Bond.
Yes. The interactive lesson includes a self-check question on Bond Angle Deviations, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Bond Angle Deviations is topic 49 of 104 in Bonding & Molecular Structure.