Molecular shapes
Count the electron pairs, name the shape, state the bond angle — three easy marks that students throw away. Flip on Test yourself to drill the angles.
Reading mode — count the electron pairs, know the shape and angle.
| Electron pairs | Shape & bond angle | Example |
|---|---|---|
| 2 bonding, 0 lone | Linear · 180° | CO2, BeCl2 |
| 3 bonding, 0 lone | Trigonal planar · 120° | BF3, SO3 |
| 4 bonding, 0 lone | Tetrahedral · 109.5° | CH4, NH4+ |
| 3 bonding, 1 lone | Trigonal pyramidal · 107° | NH3 |
| 2 bonding, 2 lone | Non-linear (bent) · 104.5° | H2O |
| 5 bonding, 0 lone | Trigonal bipyramidal · 120° and 90° | PCl5 |
| 6 bonding, 0 lone | Octahedral · 90° | SF6 |
The rule examiners want stated
Electron pairs repel and get as far apart as possible. Lone pairs repel more than bonding pairs, so each lone pair squeezes the bond angle down by about 2.5° (that's why NH3 is 107° and H2O is 104.5°, not 109.5°).
Shapes come from bonding
The electron pairs you're counting come from the bonding — get that straight and the shapes follow.
Functional groups referenceFree revision tool by Oscar Song Tutoring
Want a hand with this?
Everything here stays free. If Chemistry is where the marks keep going, I teach it one to one from the mark schemes. Free intro call, then a free first lesson.