The Period 3 elements from sodium to sulfur all burn when heated in oxygen, forming an oxide. You need to know the equations and what you would see:• Sodium: burns with a yellow (orange) flame, forming a white solid. 4Na + O2 → 2Na2O
• Magnesium: burns with a brilliant white flame, forming a white solid. 2Mg + O2 → 2MgO
• Aluminium: powdered aluminium burns with a white flame, forming a white solid. 4Al + 3O2 → 2Al2O3. A lump or foil reacts only slowly because it is protected by a layer of oxide.
• Silicon: reacts slowly on strong heating, forming a white solid. Si + O2 → SiO2
• Phosphorus: burns with a white flame, giving clouds of white smoke. P4 + 5O2 → P4O10
• Sulfur: burns with a blue flame, giving a colourless, choking gas. S + O2 → SO2In Na2O to P4O10 the oxidation state of the Period 3 element equals its number of outer electrons: +1, +2, +3, +4 and +5. Sulfur is +4 in SO2 (it only reaches +6 in SO3, which needs a catalyst to form).Worked example: balance Al + O2 → Al2O3. Two Al2O3 contain 6 O atoms, which need 3 O2, and 4 Al atoms. So 4Al + 3O2 → 2Al2O3.
• Magnesium: burns with a brilliant white flame, forming a white solid. 2Mg + O2 → 2MgO
• Aluminium: powdered aluminium burns with a white flame, forming a white solid. 4Al + 3O2 → 2Al2O3. A lump or foil reacts only slowly because it is protected by a layer of oxide.
• Silicon: reacts slowly on strong heating, forming a white solid. Si + O2 → SiO2
• Phosphorus: burns with a white flame, giving clouds of white smoke. P4 + 5O2 → P4O10
• Sulfur: burns with a blue flame, giving a colourless, choking gas. S + O2 → SO2In Na2O to P4O10 the oxidation state of the Period 3 element equals its number of outer electrons: +1, +2, +3, +4 and +5. Sulfur is +4 in SO2 (it only reaches +6 in SO3, which needs a catalyst to form).Worked example: balance Al + O2 → Al2O3. Two Al2O3 contain 6 O atoms, which need 3 O2, and 4 Al atoms. So 4Al + 3O2 → 2Al2O3.