Intermediate Topic 131 of 1102 Bonding & Molecular Structure

Odd-Electron Molecules

Free radicals such as NO and NO2 contain an unpaired electron and are often reactive.

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In-depth explanation of Odd-Electron Molecules

Species with an odd total number of valence electrons cannot have all their electrons paired, so one electron remains unpaired. Such species are called free radicals and are paramagnetic, meaning they are attracted into a magnetic field. Most radicals are highly reactive because they seek to pair the unpaired electron by bonding or by abstracting atoms from other molecules. Nitric oxide is a relatively stable exception with important biological roles, while nitrogen dioxide is a reactive pollutant. Radicals are key intermediates in combustion, polymerization and atmospheric chemistry.

Going deeper: Odd-Electron Molecules

Key ideas: Detect them by an odd valence electron count: NO has 11, NO2 has 17, ClO2 has 19. Draw the structure with the unpaired electron on the less electronegative atom or one that gives the best formal charges, as in NO2 with the electron on nitrogen. Radicals are paramagnetic, and they usually dimerize or react quickly.

Common mistakes and connections: Do not try to force an octet on every atom, or pair the electrons by guesswork. Not all radicals are very reactive, and NO and ClO2 persist. Also, paramagnetism is not exclusive to radicals, since transition metal ions show it too. Connects to MO theory, paramagnetism, chain reactions and ozone depletion.

Visualization of Odd-Electron Molecules

Nitric oxide, nitrogen dioxide and chlorine dioxide have an odd number of valence electrons, so one electron must stay unpaired and they are radicals. The interactive lesson shows this as a live animation or chart.

Worked example and use case

NO2 is a brown gas that dimerizes to colourless N2O4 at lower temperatures.

Frequently asked questions about Odd-Electron Molecules

What is Odd-Electron Molecules?

Free radicals such as NO and NO2 contain an unpaired electron and are often reactive.

Is Odd-Electron Molecules a beginner, intermediate or advanced topic?

Odd-Electron Molecules is a intermediate topic in Bonding & Molecular Structure. It builds on the vocabulary of beginner topics in this area.

What should I learn before Odd-Electron Molecules?

Study these earlier topics in Bonding & Molecular Structure first: Resonance Hybrid, Expanded Octet, Incomplete Octet.

What comes after Odd-Electron Molecules?

The next topics in Bonding & Molecular Structure are Coordinate Bond and Bond Length.

Can I practise Odd-Electron Molecules with quizzes?

Yes. The interactive lesson includes a self-check question on Odd-Electron Molecules, and the Bonding & Molecular Structure quiz draws on every topic in this area.

Where Odd-Electron Molecules fits in Bonding & Molecular Structure

Odd-Electron Molecules is topic 16 of 104 in Bonding & Molecular Structure.