Period 3 Oxides (CIE AS Chemistry)

Reactions with oxygen & chlorine

Reaction of Period 3 elements with oxygen table

Reaction of Period 3 elements with chlorine table

Reaction of sodium & magnesium with water

• Sodium reacts vigorously with cold water:

2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

• The sodium melts into a ball and moves across the water surface until it disappears
• Hydrogen gas is given off
• The solution formed is strongly alkaline (pH 14) due to the sodium hydroxide which is formed

The diagram shows the reaction of sodium with cold water

• Magnesium reacts extremely slowly with cold water:

Mg(s) + 2H₂O(l) → Mg(OH)₂(aq) + H₂(g)

• The solution formed is weakly alkaline (pH 11) as the formed magnesium hydroxide is only slightly soluble
• When magnesium is heated, it reacts vigorously with steam (water) to make magnesium oxide and hydrogen gas:

Mg(s) + H₂O(g) → MgO(s) + H₂(g)

• Oxygen is more electronegative than any of the Period 3 elements

The Pauling scale shows the electronegativities of the elements in the periodic table. Oxygen has a higher electronegativity than any of the Period 3 elements which is why the Period 3 elements will have positive oxidation states and the oxygen a negative oxidation state in the oxides of Period 3 elements

• The Period 3 elements therefore have positive oxidation states in their oxides and the oxygen has a negative oxidation state of -2

Oxidation states of the Period 3 elements in their oxides

Formulae of the oxides of the Period 3 elements & their oxidation states table

• Not all Period 3 oxides react with or are soluble in water

Reaction of Period 3 oxides with water table