--- title: "Molecular Symmetry: Elements, Operations and Point Groups" description: "Every molecule has a set of movements that leave it looking unchanged. Cataloguing them gives the molecule a label, and that label turns out to decide which orbitals can mix and which spectra can appe" canonical: https://lightmysky.com/learn/science/molecular-symmetry-elements-operations-and-point-groups-mt_KcofGO11tm source: https://lightmysky.com/learn/science/molecular-symmetry-elements-operations-and-point-groups-mt_KcofGO11tm.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Molecular Symmetry: Elements, Operations and Point Groups Every molecule has a set of movements that leave it looking unchanged. Cataloguing them gives the molecule a label, and that label turns out to decide which orbitals can mix and which spectra can appear. Subject: Science · Area: Chemistry · Ages 18 to 19 Page: https://lightmysky.com/learn/science/molecular-symmetry-elements-operations-and-point-groups-mt_KcofGO11tm ## Ready when they can - Finds the rotation axes, mirror planes, inversion centre and improper axes of a drawn molecule - Assigns a point group by working through a decision sequence rather than by recognition - Explains why a molecule with no improper axis of any kind can be chiral - Predicts from symmetry alone whether a molecule can have a permanent dipole ## Lesson: Moves that leave molecules unchanged Every molecule owns moves that leave it looking unchanged. Spins around an axis, reflections through a plane, inversion through a centre, and combined spin plus reflection moves all count. Train your eye on flat shapes first: fold the drawing in your mind and spot the axes and planes. Then carry the habit into three dimensions. Work a decision sequence, asking about each element in turn, until the molecule earns its point group label. Water is bent and keeps only a twofold axis with two mirror planes, so it is C2v. Ammonia is a pyramid with a threefold axis, so it is C3v. Boron trifluoride is a flat triangle, so it is D3h. Never guess the label from memory when the sequence answers in seconds. **Example.** Chirality falls out of the same list. A molecule with no improper axis of any kind can be chiral, while any mirror plane or improper move forbids it. So a molecule with only rotations on its list is a chirality candidate. Check the improper entries before you declare any molecule achiral. **Tip.** Polarity obeys the label too. Boron trifluoride is flat and symmetric, so its three bond dipoles cancel exactly and it stays nonpolar. Water is bent and ammonia is a pyramid, so their dipoles reinforce and both are polar. Symmetry alone tells you which molecules are even allowed a permanent dipole. **Recap.** List the unchanged moves, work the sequence, and let the label predict chirality and polarity. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Hybridisation, Conjugation and Delocalisation in Organic Molecules](https://lightmysky.com/learn/science/hybridisation-conjugation-and-delocalisation-in-organic-molecules-mt_Anv0MSQ4hq) - [Heteronuclear Diatomics and Polarity in Orbital Terms](https://lightmysky.com/learn/science/heteronuclear-diatomics-and-polarity-in-orbital-terms-mt_thdxFqyHJV) ## Opens up - [Character Tables and What Symmetry Predicts](https://lightmysky.com/learn/science/character-tables-and-what-symmetry-predicts-mt_L8cTQjeKwf)