Molecular geometry

High School

Definition

The three-dimensional arrangement of the atoms in a molecule, determined largely by the repulsion between electron pairs around the central atom. Geometry affects a molecule's polarity and how it interacts with other molecules.

Worked examples

Water (\(\)H\(_2\)O\(\)) has a bent geometry with a bond angle of ~104.5° because two lone pairs on oxygen repel the two bonding pairs.

The bent shape makes water polar, which is why it dissolves salts and other polar substances.

Methane (\(\)CH\(_4\)) has four bonding pairs around carbon and no lone pairs, giving it a tetrahedral geometry with 109.5° bond angles.

Equal repulsion in all directions creates a symmetrical, nonpolar molecule.

Ammonia (\(\)NH\(_3\)) is trigonal pyramidal — three bonds and one lone pair on nitrogen push the hydrogens closer together.

The lone pair at the top makes the molecule polar and able to form hydrogen bonds.

Common mistakes

Thinking \(\)CO\(_2\) is bent like \(\)H\(_2\)O\(\) because both have two atoms bonded to the center → \(\)CO\(_2\) is linear because carbon has no lone pairs; \(\)H\(_2\)O\(\) is bent due to two lone pairs on oxygen Lone pairs change geometry — always count both bonding and lone pairs around the central atom.
Assuming all tetrahedral molecules are nonpolar → Tetrahedral molecules like \(\)CH\(_3\)Cl\(\) can be polar if substituents differ Symmetry matters — only perfectly symmetric tetrahedral molecules (like \(\)CH\(_4\)) are nonpolar.
Ignoring lone pairs when predicting molecular shape → Include lone pairs in VSEPR theory; they occupy space and repel bonding pairs Lone pairs repel more strongly than bonding pairs, compressing bond angles and changing the shape.

Where you'll use it next

You'll apply molecular geometry when predicting molecular polarity, intermolecular forces, boiling points, and solubility in chemistry. It also appears in organic chemistry when studying reaction mechanisms and in biochemistry for understanding enzyme-substrate interactions.

Found in 1 StudyPug lesson

Mastering Molecular Geometry and VSEPR Theory

Chemistry 11

Dive into the 3D world of molecules! Our video lesson simplifies molecular geometry and VSEPR theory, helping you predict shapes, polarity, and reactivity. Perfect for building your chemistry foundation!

11th Grade11th