Group 7 (VII) displacement reactions
In a displacement reactionIs a reaction in which a more reactive metal takes the place of a less reactive metal in a compound., a more reactive halogen (Cl2, Br2, I2) is added to a halide solution. The more reactive halogen pushes out and replaces the less reactive halogen.
Chlorine is more reactive than the iodine in potassium iodide solution:
| Word equation: | chlorine + potassium iodide 鈫 iodine + potassium chloride |
| Symbol equation: | Cl2(g) + 2KI(aq) 鈫 I2(aq) + 2KCl(aq) |
| Ionic equation: | Cl2(g) + 2I-(aq) 鈫 I2(aq) + 2Cl-(aq) |
| Word equation: | Symbol equation: |
|---|---|
| chlorine + potassium iodide 鈫 iodine + potassium chloride | Cl2(g) + 2KI(aq) 鈫 I2(aq) + 2KCl(aq) |
| Word equation: | Ionic equation: |
|---|---|
| chlorine + potassium iodide 鈫 iodine + potassium chloride | Cl2(g) + 2I-(aq) 鈫 I2(aq) + 2Cl-(aq) |
Observations: the colourless solution changes to brown
Chlorine is also more reactive than the bromine in potassium bromide solution:
| Word equation: | chlorine + potassium bromide 鈫 bromine + potassium chloride |
| Symbol equation: | Cl2(g) + 2KBr(aq) 鈫 Br2(aq) + 2KCl(aq) |
| Ionic equation: | Cl2(g) + 2Br-(aq) 鈫 Br2(aq) + 2Cl-(aq) |
| Word equation: | Symbol equation: |
|---|---|
| chlorine + potassium bromide 鈫 bromine + potassium chloride | Cl2(g) + 2KBr(aq) 鈫 Br2(aq) + 2KCl(aq) |
| Word equation: | Ionic equation: |
|---|---|
| chlorine + potassium bromide 鈫 bromine + potassium chloride | Cl2(g) + 2Br-(aq) 鈫 Br2(aq) + 2Cl-(aq) |
Observations: the colourless solution changes to orange
When a Group 7 element reacts, it gains one electron to form a negative ion with a stable electronic configuration 鈥 a full outer shell.
As we move down the column of Group 7 elements, their reactivity decreases. In each, the outer shell is further from the nucleus and the incoming electron is not as easily attracted to it.
Half equations can be used to represent these reactions (higher tier):
Chloride ions from a chlorine molecule:
Cl2 +2e- 鈫 2Cl-
A chloride ion from a chlorine atom:
Cl +e- 鈫 Cl-