What a learner can do afterwards
- Writes equations for sodium oxide and for sulfur trioxide reacting with water
- Links the change from ionic to covalent bonding across the row to the change from basic to acidic
- Explains what amphoteric means using aluminium oxide with acid and with alkali
- Predicts the approximate pH of the solution a named period 3 oxide makes
1 · Read
The left of the row gives alkalis. Sodium oxide meets water to make sodium hydroxide solution: Na2O plus H2O gives 2NaOH. Magnesium oxide does the same basic job. These oxides are ionic, and their solutions turn alkaline.
The right of the row gives acids. Sulfur trioxide meets water to make sulfuric acid: SO3 plus H2O gives H2SO4. Phosphorus oxides do the same acidic job. These oxides are covalent, and their solutions turn acidic.
Aluminium oxide sits on the fence and reacts both ways. It takes on acids to give a salt plus water, and it takes on alkalis to give an aluminate. Oxides that behave like this are called amphoteric.
To predict a pH, read the bonding. Metal oxides from the left give pH above 7, non-metal oxides from the right give pH below 7, and aluminium oxide offers no simple pH.
Ionic oxides turn water alkaline, covalent oxides turn it acidic, and aluminium oxide does both.
2 · Watch
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Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.