2.3 Group 7 the halogens Flashcards
Describe the trend in atomic radius down the group
Atomic radius increases down the group.
Why does atomic radius increase down the group
The atoms increase in size due to additional electron shells.
Describe the trend in reactivity down the group
Reactivity decreases.
Why does reactivity decrease down the group
- Group 7 elements need to gain an electron
- Weaker attraction between nucleus and outer shell due to greater atomic radius and increased shielding
- Harder to attract an electron, so reactivity decreases
Describe the trend in first ionisation energy down the group
Decreases down the group.
Why does first ionisation energy decrease down the group
- Weaker attraction between nucleus and electron being removed due to a greater atomic radius and increased shielding
- Less energy required to remove the electron
Describe the trend in boiling point down the group
Boiling point increases down the group
Explain why boiling point increases down the group
- Group 7 elements are simple covalent molecules held together by van der waals forces
- Down the group, the Ar increases/more electrons
- Causes van der waals forces to be stronger, so more energy required to overcome them
Describe the trend in oxidising power down the group
Oxidising power decreases down the group
Why does oxidising power decrease down the group
- Weaker attraction between nucleus and outer shell
- Atoms less able to attract an electron (harder to be reduced)
- Causes oxidising power to decrease
Describe and explain the trend in reducing power down the group
- Reducing power increases down the group
- Atomic radius increases, so outer electron more easily lost as there is a weaker attraction between the nucleus and outer shell
What is the equation for the reaction between fluoride ions and sulfuric acid
NaF + H2SO4 => NaHSO4 + HF
What is the equation for the reaction between chloride ions and sulfuric acid
NaCl + H2SO4 => NaHSO4 + HCl
What are the equations for the 2 reactions between bromide ions and sulfuric acid
NaBr + H2SO4 => NaHSO4 + HBr
2HBr + H2SO4 => Br2 + SO2 + 2H2O
What are the equations for the 3 reactions between iodide ions and sulfuric acid
NaI + H2SO4 => NaHSO4 + HI
2HI + H2SO4 => I2 + SO2 + 2H2O
6HI + SO2 => H2S + 3I2 + 2H20
What is the relationship between reducing power and length of reaction
The greater the reducing power, the longer the reaction as the halide is powerful enough to reduce more species.
What is used to test for halide ions
Acidified silver nitrate and ammonia.
What happens when silver nitrate is added to chloride ions
A white precipitate forms (AgCl).
What happens when silver nitrate is added to bromide ions
A cream precipitate forms (AgBr).
What happens when silver nitrate is added to iodide ions
A yellow precipitate forms (AgI).
What happens when dilute ammonia (NH3) is added to chloride ions
The precipitate dissolves.
What happens when dilute ammonia (NH3) is added to iodide ions
No change.
What happens when dilute ammonia (NH3) is added to bromide ions
No change.
What happens when concentrated ammonia (NH3) is added to chloride ions
The precipitate dissolves.
What happens when concentrated ammonia (NH3) is added to bromide ions
The precipitate dissolves.
What happens when concentrated ammonia (NH3) is added to iodide ions
No change.
What is a disproportionation reaction
A reaction in which the same species is both oxidised and reduced.
What is the equation for the reaction between chlorine and cold alkali
Cl2(aq) + 2NaOH(aq) => NaCl(aq) + NaClO(aq) + H2O(l)
What is the equation for the reaction between chlorine and water
Cl2(aq) + H2O(l) => HCl(aq) + HClO(aq)
What is the equation for the reaction between chlorine and sunlight (UV light)
2Cl2 + 2H2O => 4HCl + O2
How do you test for sulfate ions (SO4^2-)
Adding BaCl2, reacts to form a while precipitate.
How do you test for hydroxide ions (OH-)
Use red litmus paper which will turn blue.
How do you test for carbonate ions (CO3^2-)
- When you add an acid (e.g. HCl), the substance containing the carbonate ions will fizz and CO2 is given off
- This can be collected and bubbled through limewater which will turn cloudy
