Period 3 Elements & Oxides (A2 Only)
Chemistry: AQA A Level, topic 4.1.1
Reactions of the Third Period with Water
The Third Period elements show many interesting reactions with water.
Reactions of Na with water
- 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
- This reaction is vigorous with cold water.
- The solution you get is highly basic.
Reactions of Mg with water
- Mg(s) + 2H2O(l) → Mg(OH)2(aq) + H2(g)
- This reaction is slow with cold water.
Reactions of Mg with steam
- Similarly, if you react magnesium with steam, you get magnesium oxide.
- Mg(s) + H2O(g) → MgO(s) + H2(g)
- This is a vigorous reaction and makes the Mg burn with a white light.
Reactions of the Third Period with Oxygen
The elements of the third period have distinctive and different reactions with oxygen.
Na, Mg, Al oxides
- The equations are:
- 4Na(s) + O2(g) → 2Na2O(s)
- 2Mg(s) + O2(g) → 2MgO(s)
- 4Al(s) + 3O2(g) → 2Al2O3(s)
- The common feature is that these metals form their normal ions: Na+, Mg2+ and Al3+.
- To work out the equations, you just have to balance the overall charge with oxide ions.
Silicon and phosphorus oxides
- These oxides are covalent materials. The reactions for their formation are:
- Si(s) + O2(g) → SiO2(s)
- P4(s) + 5O2(g) → P4O10(s)
- Both of these get the oxidation state of their group:
- Phosphorus is +5 and in group 5.
- Silicon is +4 and in group 4.
Sulfur
- Sulfur can form multiple oxides. The most common are sulfur dioxide and sulfur trioxide.
- The equation for the formation of sulfur dioxide is:
- S8(s) + 8O2(g) → 8SO2(g)
- Sulfur trioxide is made from sulfur dioxide using a catalyst. The equation is:
- 2SO2(g) + O2(g) 2SO3(g)
Test yourself on Period 3 Elements & Oxides (A2 Only)
What is the product of the reaction between magnesium and steam?
Which of the following describes silicon and phosphorus oxides?
Why are sulfur oxides different to the oxides of other elements in the third period?