Chemguide: Support for CIE A level Chemistry

The Periodic Table

Learning outcome 9.2.3 and part of 9.2.6

Statement 9.2.3 deals with the reactions of the oxides of the elements in Period 3 with water. 9.2.6 is involved in the explanation for this.

Before you go on, you should find and read the statements in your copy of the syllabus.

Remember that we are only dealing with the oxides:

Na₂O, MgO, Al₂O₃, SiO₂, P₄O₁₀, SO₂ and SO₃.

The reactions between these oxides and water are found on the page acid-base behaviour of the period 3 oxides. That page contains a lot of information, and if you try to absorb it all in one go, you risk getting really confused.

For each oxide, you will find an introduction, its reaction with water (if any), and its reaction with acids or bases. For the purposes of this statement, just read the introduction to each oxide, and its reaction with water. Make notes on what the syllabus wants you to know. Ignore everything else!

Remember that you don't need to know about phosphorus(III) oxide, or the oxides of chlorine.

Summary of what you need to get from this page

• You need to know how each of these oxides reacts with water (if they do) and what is formed (if anything). You also need to be able to write equations for the reactions that occur.

• You need to understand that the oxides at the left-hand end of the period are ionic, containing oxide ions, and that the rest are covalent. Whether an oxide is ionic or covalent depends on the electronegativity difference between the element and oxygen.

  In all of these oxides, oxygen is the most electronegative element. However, electronegativity increases across a period, and from silicon onwards, there isn't enough electronegativity difference between the element and oxygen for the oxide to be ionic.

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