Chemical bonding &
molecular geometry

Count valence electrons, connect the atoms, complete terminal octets, and place the remaining electrons on the central atom. If the center still lacks an octet, consider multiple bonds. A Lewis structure tells you which atoms are bonded; it does not by itself show every bond in its final spatial direction.

Example: water

H—O—H

Oxygen makes two O–H bonds and has two lone pairs. Four electron regions surround O, even though only two atoms are attached to it. Rotate the H₂O model ↗

Draw formal charges where needed. For example, a useful nitric acid contributor is H–O–N⁺(=O)–O⁻; the two non-protonated oxygen positions exchange through resonance. See HNO₃ ↗

VSEPR counts electron regions around a central atom. A single, double, or triple bond counts as one region; each lone pair counts as one region. Two regions suggest a linear arrangement, three trigonal planar, and four tetrahedral electron geometry. Lone pairs occupy regions but are omitted when naming the molecular shape.

CO₂ · AX₂Linear

Two bonding regions at C, no lone pairs at C. The O=C=O directions oppose each other.

View CO₂ ↗

H₂O · AX₂E₂Bent

Two bonds and two lone pairs at O. The H–O–H bonds do not point in opposite directions.

View H₂O ↗

Actual angles can depart from ideal VSEPR values, especially when lone pairs, multiple bonds, or ring strain matter. Our 3D viewer shows model geometry; it is not a replacement for an experimentally measured angle. Use the VSEPR shape guide for the full AXE table.

A polar bond has an uneven electron distribution. Molecular polarity also depends on the direction of every bond dipole in space. Equal dipoles cancel when symmetry points them in opposing directions; otherwise the molecule can retain a net dipole. Do not decide from a single bond or from the molecular formula alone.

BF₃Nonpolar molecule

The three B–F bonds are polar, but their trigonal-planar directions cancel.

Inspect BF₃ ↗

NH₃Polar molecule

Three N–H bonds form a trigonal pyramid; the bond contributions do not cancel.

Inspect NH₃ ↗

“Nonpolar” in introductory organic chemistry can be a practical classification for hydrocarbons with only small dipoles. It does not always mean an exactly zero measured dipole. Try the polarity checker ↗

Two substances can share a formula while differing in connectivity or geometry. In cis-1,2-dichloroethene, the chlorine substituents sit on the same side of a rigid C=C bond; in the trans isomer they sit on opposite sides. This changes whether the C–Cl dipoles reinforce or cancel.

C₂H₂Cl₂ · CISPolar

Same-side chlorine substituents reinforce their dipole components.

View cis isomer ↗

C₂H₂Cl₂ · TRANSNonpolar

Opposite substituents give cancellation in the planar trans arrangement.

View trans isomer ↗

Single bonds can rotate, so a 3D conformer is one pose of a flexible molecule. 1,2-dichloroethane is a useful case: the C–Cl directions change as the C–C bond rotates. Resonance is different: contributors change the electron drawing, not the atomic connectivity.