Oxide

An oxide is a chemical compound. It must contain at least one oxygen atom and one other element. You can find these compounds almost everywhere. In fact, most of the Earth's crust is made of oxides. Even materials that look like pure elements often have an oxide coating. For example, aluminum foil grows a thin skin called a passivation layer. This layer acts like a shield. It protects the foil from further oxidation.

Oxides come in many different shapes and sizes. Some are very simple and are called binary oxides. These contain only oxygen and one other element. A good example is carbon monoxide or carbon dioxide. Other oxides are much more complex. They can include many different parts, like extra ions. The mineral fayalite is a ternary oxide. This means it has three parts, such as iron, silicon, and oxygen. Some metal oxides can even have different structures. Titanium dioxide is a famous example because it has three distinct structures.

Many different ways can create an oxide. Some metal oxides form when you heat other compounds. For instance, heating limestone breaks it down into calcium oxide. This process also releases carbon dioxide gas. Other metals form oxides by reacting with oxygen in the air. This can lead to corrosion in iron. Sometimes, workers use a process called roasting to make oxides. They heat metal sulfide minerals in the air. This turns molybdenite into molybdenum trioxide. This trioxide is used to make almost all molybdenum compounds.

We can also use oxides to get pure metals. This is often done through a process called reduction. One way is thermal decomposition, which means using heat to break a compound apart. For example, silver oxide decomposes at 200 °C. Another way uses a chemical reagent. Carbon in the form of coke is a common and cheap reducing agent. This is how people smelt iron ore. Other non-metal oxides are very common in our world. Carbon dioxide and carbon monoxide form when carbon reacts with oxygen. Nitrogen can also form oxides, like nitric oxide, through combustion.

Oxides can be found in many states of matter. Some are gases, like carbon dioxide. Others are crystalline solids, like many metal oxides. Some oxides can even dissolve in liquids. Adding an aqueous base to certain oxides can create oxyanions. This is a way of describing how they change in water. You might know about sulfuric acid, which is made on a huge scale. It starts by oxidizing sulfur to sulfur dioxide. Then, it is oxidized again to become sulfur trioxide. Finally, a hydration reaction turns it into sulfuric acid.