Multiple choiceQuestion 1 · Recall
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By the end you can write balanced equations for the reactions of Period 3 elements with oxygen, chlorine and water, and describe what you would actually see in each case.
Period 3 runs . It starts with a reactive metal and ends with a noble gas that does nothing at all.
The chemistry shifts steadily rightwards: metals lose electrons, non-metals gain them, and the middle element (aluminium) is the awkward in-betweener.
That single idea explains almost every reaction in this lesson — how violently the element reacts, and whether its oxide turns out basic or acidic.
Heat a Period 3 element in air or oxygen and you usually get its oxide. The metal oxides are ionic and solid; the non-metal oxides are covalent and often gaseous.
| element | equation | what you see |
|---|---|---|
| sodium | yellow flame, white solid | |
| magnesium | brilliant white flame, white solid | |
| aluminium | a tough oxide layer forms first, which protects the metal | |
| silicon | needs strong heating; white solid | |
| phosphorus | catches fire on its own, thick white smoke | |
| sulfur | pale blue flame, choking gas |
Notice that sodium and magnesium burn easily because their outer electrons are cheap to lose. Silicon and sulfur need help — a flame, or strong heating.
Under normal burning conditions sulfur gives sulfur dioxide, not sulfur trioxide. is made industrially with a vanadium(V) oxide catalyst.