• A direct combination reaction is a reaction in which two or more substances join to form one new, more complex substance.
• General pattern A + B → AB
• Think of two separate objects snapping together. Typical examples:

Metal + oxygen → metal oxide

Non-metal + oxygen → non-metal oxide

Metal + non-metal → salt

• Activity: reaction of metals with oxygen. Using tongs, a student heats three samples in a Bunsen flame for the same time: a sanded magnesium ribbon, a piece of steel wool (iron) and a copper wire.
• Observations and conclusions:

• Conclusion most metals combine with oxygen when heated in air, but they do so with very different vigour.
• Magnesium reacts most readily, iron less so, and copper least.
• So magnesium is more reactive than iron, and iron is more reactive than copper.

• Safety note. Burning magnesium gives out very intense light and ultraviolet radiation that can injure the retina.
• Never stare at it; wear safety goggles.
• Notice how each equation is balanced.
• In 2Mg + O₂ → 2MgO there are two Mg atoms and two O atoms on each side.
• In 3Fe + 2O₂ → Fe₃O₄ there are three Fe and four O atoms on each side.
• In 2Cu + O₂ → 2CuO there are two Cu and two O on each side.
• The oxygen molecule O₂ always contains two atoms, so we must produce an even number of oxygen atoms on the left.
• Other direct combination examples you can understand with the same pattern: 2Na + Cl₂ → 2NaCl (a metal and a non-metal give a salt), and Fe + S → FeS (heating iron and sulphur).
• Also, magnesium combines directly with bromine: Mg + Br₂ → MgBr₂.