BackOxides, Peroxides, and Superoxides: Properties, Formulas, and Reactions
Study Guide - Smart Notes
Tailored notes based on your materials, expanded with key definitions, examples, and context.
Oxides, Peroxides, and Superoxides
Introduction to Oxygen Anions
Oxides, peroxides, and superoxides are important classes of compounds formed by the reaction of oxygen with metals. These compounds differ in the number of oxygen atoms and the charge of the oxygen-containing anion. Understanding their formulas, properties, and reactions is essential in general chemistry, especially when studying periodic trends and chemical reactivity.
Oxides contain the O2− ion.
Peroxides contain the O22− ion.
Superoxides contain the O2− ion.
Group 1A and 2A metals commonly form these compounds by direct combination with oxygen.
Classification and Formulas of Oxygen Anions
The following table summarizes the types of oxygen anions found in oxides, peroxides, and superoxides, along with their formulas and charges.
Type | Formula | Charge | Example |
|---|---|---|---|
Oxide | O2− | -2 | Na2O |
Peroxide | O22− | -2 | Na2O2 |
Superoxide | O2− | -1 | KO2 |
Memory Tool: "One Two Two One" helps recall the number of oxygen atoms and charges: Oxides (1 O, 2−), Peroxides (2 O, 2−), Superoxides (2 O, 1−).
Writing Formulas for Oxides, Peroxides, and Superoxides
To write the formula for a compound containing a specific oxygen anion, combine the metal cation with the appropriate oxygen anion, balancing charges to achieve a neutral compound.
Oxide Example: Sodium oxide:
Peroxide Example: Sodium peroxide:
Superoxide Example: Potassium superoxide:
Practice: Classify and write formulas for the following:
Li2O: Oxide
Na2O2: Peroxide
KO2: Superoxide
MgO: Oxide
Periodic Trends in Formation of Oxygen Compounds
The ability of metals to form peroxides and superoxides decreases as you move down Group 1A. Group 2A metals do not form superoxides under normal conditions.
Group 1A metals: Can form oxides, peroxides, and superoxides (e.g., Li forms oxide, Na forms peroxide, K forms superoxide).
Group 2A metals: Typically form only oxides and peroxides.
Reactions Involving Oxides, Peroxides, and Superoxides
These compounds are often formed by direct reaction of metals with oxygen gas. The type of product depends on the metal and reaction conditions.
General Reaction:
Example: (formation of barium peroxide)
Example: (formation of potassium superoxide)
Summary Table: Oxides, Peroxides, and Superoxides
Type | General Formula | Oxygen Anion | Example | Formation |
|---|---|---|---|---|
Oxide | M2O | O2− | Li2O | Li + O2 → Li2O |
Peroxide | M2O2 | O22− | Na2O2 | Na + O2 → Na2O2 |
Superoxide | MO2 | O2− | KO2 | K + O2 → KO2 |
Additional info: Superoxides are less common and typically form only under specific conditions, such as high oxygen pressure or with larger alkali metals.
