Chemistry electron domain geometry

Base shape and bond angle for 2 electron domains

Electron Domain Geometry: Linear | Bond Angle: 180°

Base shape and bond angle for 3 electron domains

Electron Domain Geometry: Trigonal Planar | Bond Angle: 120°

Base shape and bond angle for 4 electron domains

Electron Domain Geometry: Tetrahedral | Bond Angle: 109.5°

Molecular geometry: 2 bonding domains, 0 non-bonding domains

Linear (180°)

Molecular geometry: 3 bonding domains, 0 non-bonding domains

Trigonal Planar (120°)

Molecular geometry: 2 bonding domains, 1 non-bonding domain

Bent or V-shaped (<120°)

Molecular geometry: 4 bonding domains, 0 non-bonding domains

Tetrahedral (109.5°)

Molecular geometry: 3 bonding domains, 1 non-bonding domain

Trigonal Pyramidal (<109.5°)

Molecular geometry: 2 bonding domains, 2 non-bonding domains

Bent or V-shaped (<109.5°)

Effect of non-bonding electron pairs (lone pairs) on bond angles

Lone pairs exert greater repulsion than bonding pairs, which pushes bonding domains closer together and decreases the bond angle.

Geometry & bond angle for CO2 and HCN

Linear (180°)

Geometry & bond angle for BF3 and NO3-

Trigonal Planar (120°)

Geometry & bond angle for SO2 and O3

Bent / V-shaped (<120°)

Geometry & bond angle for CH4, NH4+, and ClO4-

Tetrahedral (109.5°)

Geometry & bond angle for NH3, H3O+, and PBr3

Trigonal Pyramidal (<109.5°)

Geometry & bond angle for H2O, NH2-, and SF2

Bent / V-shaped (<109.5°)

Comparison between Trigonal Planar and Trigonal Pyramidal

Trigonal Planar has 3 bonds and 0 lone pairs (120°). Trigonal Pyramidal has 3 bonds and 1 lone pair (<109.5°).

Difference between 3-domain Bent and 4-domain Bent

3-domain Bent: 2 bonds + 1 lone pair (<120°). 4-domain Bent: 2 bonds + 2 lone pairs (<109.5°).

Effect of multiple bonds (double/triple bonds) on domain count and repulsion

Multiple bonds count as a single electron domain, but they exert greater repulsion than single bonds, slightly modifying bond angles.

Bond angles in ethene (C2H4)

H-C=C angle is 121.5° (greater repulsion from double bond). H-C-H angle is 117°.

How electron domain geometry differs from molecular geometry

Electron domain geometry considers ALL domains (bonding + non-bonding). Molecular geometry considers ONLY the spatial arrangement of the atoms (bonding domains).

Electron domain geometry vs molecular geometry for H2O

Electron Domain Geometry: Tetrahedral | Molecular Geometry: Bent / V-shaped

Electron domain geometry vs molecular geometry for NH3

Electron Domain Geometry: Tetrahedral | Molecular Geometry: Trigonal Pyramidal

Electron domain geometry vs molecular geometry for SO2

Electron Domain Geometry: Trigonal Planar | Molecular Geometry: Bent / V-shaped

Summary rule for bond angles when lone pairs are present

Whenever 1 or more lone pairs are present on the central atom, place a '<' sign before the theoretical base angle (120° or 109.5°).