► What is rust? – Henry E., age 13, Boston, Massachusetts

Imagine leaving your shiny metal bicycle outside in the rain. As water pools on its surfaces, oxygen from the air lingers nearby, and together they begin to quietly attack the metal.

The iron in the bike and the oxygen and water in the environment together undergo a chemical reaction. It forms iron oxide – better known as rust – which accumulates over time. This reddish-brown, flaky substance is more than just ugly; it’s a sign that the metal is breaking down.

Chemists call this process oxidation. You can think of iron as like a superhero — tough, durable and shiny — until it meets its kryptonite: moisture and air. Water helps iron atoms more easily shed their electrons, which are negatively charged particles. Oxygen acts like

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