1. Noble Metals:
* High Electronegativity: Gold and platinum have high electronegativity, meaning they have a strong hold on their electrons and resist losing them to form chemical bonds with other elements. This makes them very stable and unreactive.
* Inertness: These metals are considered "noble metals" due to their inertness. They are highly resistant to oxidation, which is the process of reacting with oxygen to form oxides. Oxides are often responsible for corrosion in other metals.
2. Lack of Reactivity:
* Strong Metallic Bonds: Gold and platinum have strong metallic bonds within their structures. These bonds are difficult to break, making them resistant to chemical attacks from the environment.
* Low Reactivity with Oxygen: While they can react with oxygen at very high temperatures, they don't readily react with oxygen at normal temperatures and pressures. This is why they don't form oxides and corrode in moist air.
3. Surface Protection:
* Protective Oxide Layer: While not as prominent as in some other metals, gold and platinum can form thin, very stable oxide layers on their surfaces. These layers act as a barrier, protecting the metal from further corrosion.
4. Exception:
* Aqua Regia: Although generally resistant to corrosion, gold can be dissolved in a mixture of concentrated nitric acid and hydrochloric acid, known as aqua regia. This is because the mixture creates a complex ion that allows gold to dissolve.
Conclusion:
The combination of their high electronegativity, inertness, strong metallic bonds, and protective oxide layers makes gold and platinum highly resistant to corrosion in moist air. This is why they are often used for jewelry, coins, and other applications where durability is crucial.
