Molecular Geometry and Polarity

Manual: General · Subject: Chemistry

Predict three-dimensional shapes and connect them to polarity and intermolecular behavior.

From electron pairs to shape

VSEPR theory

Valence-shell electron-pair repulsion theory predicts that electron domains arrange themselves to minimize repulsion. Lone pairs repel more strongly than bonding pairs, so they compress bond angles.

Common molecular shapes

Electron domains	Shape	Typical bond angle
2	Linear	$180^\circ$
3	Trigonal planar	$120^\circ$
4	Tetrahedral	$109.5^\circ$
4 with 1 lone pair	Trigonal pyramidal	Less than $109.5^\circ$
4 with 2 lone pairs	Bent	Less than $109.5^\circ$

Polarity

A molecule is polar when its bond dipoles do not cancel. Molecular polarity depends on both bond polarity and shape. For example, $CO_2$ has polar bonds but is nonpolar overall because it is linear and symmetric.

What is the molecular shape of $CH_4$ ?

Linear Trigonal planar Tetrahedral Bent

Why are bond angles in $NH_3$ smaller than $109.5^\circ$ ?

Polar vs nonpolar molecules

Polar

Uneven charge distribution
Has a net dipole moment
Often higher boiling point than similar nonpolar molecules

Nonpolar

Symmetric or balanced charge distribution
No net dipole moment
Often weaker intermolecular attractions

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Shape-first reasoning

To predict polarity, draw the Lewis structure, count electron domains, determine shape, then assess whether the dipoles cancel.

Which molecule is nonpolar despite having polar bonds?

H_2O

NH_3

CO_2

SO_2

Neuroanatomy Explorer

Memory Deck

Match the Pairs

Concept Constellation

Molecular Geometry and Polarity

From electron pairs to shape

VSEPR theory

Polarity

Polar vs nonpolar molecules