How does copper change when exposed to moist carbon dioxide in the air, and what is the green substance formed on copper surfaces as a result of this reaction?

When copper is exposed to moist carbon dioxide in the air, it undergoes oxidation to form copper carbonate. The reaction involves the copper surface reacting with carbon dioxide (CO₂) and water (H₂O) from the air. Over time, a greenish layer of copper carbonate develops on the copper surface, creating the characteristic patina. This green substance is often identified as basic copper carbonate, and its chemical formula is typically a combination of copper(II) hydroxide (Cu(OH)₂) and copper(II) carbonate (CuCO₃). The patina acts as a protective layer, preventing further corrosion and giving aged copper items, such as statues or roofs, their distinctive appearance.