Molecular Geometry Chart
The shape of a molecule depends on both its electron groups and the presence of lone pairs. Electron geometry considers all electron groups, while molecular geometry describes only the arrangement of atoms.
When electrons repel each other, they create predictable arrangements that minimize repulsion. For example, with 2 electron groups, molecules form a linear shape with 180° bond angles (like CO₂). With 3 electron groups and no lone pairs, molecules adopt a trigonal planar arrangement with 120° angles.
Lone pairs significantly affect molecule shape. A molecule with 4 electron groups but 1 lone pair creates a trigonal pyramidal structure (like NH₃) rather than tetrahedral, with bond angles less than 109.5°. Similarly, a molecule with 2 lone pairs forms a bent structure (like H₂O).
💡 Remember: Lone pairs take up more space than bonding pairs, which causes bond angles to decrease from their ideal values!
As electron groups increase to 5 or 6, more complex geometries emerge, including trigonal bipyramidal and octahedral arrangements. The presence of lone pairs in these structures creates specialized shapes like seesaw, T-shaped, and square pyramidal.