Ozone (O₃) — Properties, Uses & Safety

Overview

Ozone (O3) is a pale blue gas with a distinctive pungent smell and a molar mass of 47.998 g/mol. It is an allotrope of oxygen, consisting of three oxygen atoms bonded in a bent molecular geometry with a bond angle of approximately 117 degrees. Ozone is a powerful oxidizing agent and plays a dual role in Earth's atmosphere — beneficial in the stratosphere but harmful at ground level. In the stratosphere at 15 to 35 km altitude, the ozone layer absorbs 97 to 99% of the Sun's harmful ultraviolet UV-B and UV-C radiation, protecting life on Earth from DNA damage, skin cancer, and cataracts. The depletion of this protective layer by chlorofluorocarbons (CFCs) led to the Montreal Protocol, one of the most successful international environmental agreements. At ground level, ozone is a major component of photochemical smog and a respiratory irritant. Ozone carries several GHS hazard codes including H270 (may cause or intensify fire as an oxidizer), H332 (harmful if inhaled), H314 (causes severe skin burns and eye damage), and H335 (may cause respiratory irritation). Industrially, ozone is used for water purification, air treatment, bleaching of textiles and paper, and food sterilization. It is generated on-site using electrical discharge through oxygen because it decomposes rapidly back to O2. For chemistry students, ozone is a fascinating molecule for exploring resonance structures — the two equivalent O-O bonds in ozone are best described as a resonance hybrid with a bond order of 1.5, intermediate between a single and double bond. Ozone also connects to lessons on allotropy (comparing O2 and O3), oxidation-reduction reactions, atmospheric chemistry, and the kinetics of catalytic ozone destruction by free radicals. The story of ozone depletion and recovery is a compelling real-world example of how chemistry knowledge directly informs environmental policy.

IUPAC Name

ozone

CAS Number

10028-15-6

PubChem CID

24823

Molecular Formula

O₃

Molar Mass

47.998 g/mol

State at STP

gas

Appearance

Pale blue gas with distinctive pungent smell