Oxide

Quick Facts

Formula: O²⁻

Pronunciation: OK-side

Etymology: Oxygen + -ide

Meaning: The negative ion of oxygen, or a compound containing oxygen bonded to another element.

What It Really Means

Oxide is the most common oxygen-containing ion in inorganic chemistry, and it is the building block of thousands of compounds. Rust is iron oxide. Sand is silicon dioxide. Lime is calcium oxide. But here is the important thing. Not all oxides behave the same way. Some are basic, some are acidic, and some are amphoteric. Metal oxides like sodium oxide are basic. They react with water to form hydroxides and with acids to form salts. Non-metal oxides like carbon dioxide are acidic. They react with water to form acids and with bases to form salts. Amphoteric oxides like aluminium oxide react with both acids and bases. The type of oxide depends on the element it is bonded to. Now here is a common confusion. Oxide, peroxide, and superoxide are three different things. Oxide is O2 minus. Peroxide is O2 2 minus, with an O-O bond. Superoxide is O2 minus, with a different electron count. Peroxides and superoxides behave very differently from oxides. They are often strong oxidizing agents. So do not assume that oxide, peroxide, and superoxide are interchangeable. They are not. Each has its own structure and its own chemistry. Learning the differences now will save you confusion later.

Common Examples

• Iron oxide (Fe₂O₃)
• Carbon dioxide (CO₂)
• Aluminium oxide (Al₂O₃)
• Calcium oxide (CaO)

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