Group 7,the halogens Flashcards
Describe the state in which each of the halogens exist at room temperature
1) fluorine (F2) is a pale yellow gas
2) chlorine (Cl2) is a greenish gas
3) bromine (Br2) is a red-brown liquid
4) iodine (I2) is a black solid
What is the trend in electronegativity as you go down group 7
The electronegativity decreases as you go down group 7
What happens to the size of the atoms as you go down group 7
They get bigger as each element has one extra filled main level of electrons compared to the one before it.
Define electronegativity
Electronegativity is a measure of an atoms ability to attract electrons, or electron density towards itself in a covalent bond.
What is the trend in melting and boiling points as you go down group seven
The melting and boiling points increase because the atoms get bigger/have more electrons so the Van Der Waals forces are stronger.
What is the link between boiling point and volatility for group 7 elements
The lower the boiling point, the more volatile the element.
Explain why the electronegativity of the H—X bond (and halogens in general) decreases as you go down the group
- The shared electrons in the H—X bond get further away from the nucleus as the atoms get larger going down the group.
- This makes the shared electrons further from the halogen nucleus and increases the shielding by more inner shells of electrons.
- These factors are more important than the increasing nuclear charge, so electronegativity decreases down the group.
What is the trend in the oxidising ability of the halogens as you go down the group
The oxidising ability of the halogens decreases as you go down the group
Which halogen is one of the most powerful oxidising agents known
Fluorine.
How do halogens undergo displacement reactions
Halogens with react with metal halides in such a way that the halide in the compound will be replaced with a more reactive halogen, but not by a less reactive one.
When halogens undergo a displacement reaction with a metal halide, what is the oxidising agent
The more reactive halogen that is displacing the less reactive one.
What oxidation state do halogens always have
Halogens always go from an oxidation state of 0 to an oxidation state of -1 when reacting with a metal
What is the trend in the reducing power of a halogen as you go down the group
The reducing power of the halogens increases as you go down the group
How do halide ions act as reducing agents
They lose electrons and become halogen molecules
What type of reaction demonstrates the differing reducing powers of the halogens
The reaction of solid sodium halides with concentrated sulphuric acid
Describe the reaction between solid sodium chloride and concentrated sulphuric acid
Equation: NaCl + H2SO4 —> NaHSO4 + HCl
What happens:
- drops of concentrated sulphuric acid are added to solid sodium chloride.
- steamy fumes of hydrogen chloride are seen
- The solid product is sodium hydrogensulfate
- This reaction can be used to prepare hydrogen chloride gas
Why is the reaction between solid sodium chloride and concentrated sulfuric acid not a redox reaction
- No oxidation states have changed
- The chloride ion is too weak a reducing agent to reduce the sulfur oxidation state (+6) in sulfuric acid
- It is an acid-base reaction.
How many reactions occur when solid sodium bromide reacts with concentrated sulfuric acid
Two
Describe the first reaction that occurs when solid sodium bromide reacts with concentrated sulfuric acid
Equation: NaBr + H2SO4 —> NaHSO4+ HBr
What happens:
- sodium hydrogensulfate and hydrogen bromide are produced in an acid-base reaction.
- This is similiar to the reaction os solid sodium chloride with concentrated sulfuric acid.
Describe the second reaction that occurs when solid sodium bromide reacts with concentrated sulfuric acid
Equation: 2H+ + 2Br- + H2SO4 —> SO2 + 2H2O + Br2
What happens:
- the bromide ions are strong enough reducing agents to reduce the sulfuric acid to sulfur dioxide.
- The oxidation state of the sulfur is reduced from +6 to +4
- the oxidation state of the bromine increases from -1 to 0
- This is a redox reaction.
Summarise what happens when solid sodium bromide reacts with concentrated sulfuric acid
- Two reactions occur
- You see steamy fumes of hydrogen bromide and bromine.
- Colourless sulfur dioxide is also formed
Describe what happens when solid sodium iodide reacts with concentrated sulfuric acid
- You see steamy fumes of hydrogen iodide, the black solid iodine and hydrogen sulphide gas
- solid yellow sulfur may also be seen and colourless sulfur dioxide
- Several reactions occur
- Hydrogen iodide is produced in an acid-base reaction as before
- Iodide ions are better reducing ions than bromide ions so they reduce the sulfur in sulfur dioxide even further (from +6 to 0 and -2) so sulfur dioxide, sulfur and hydrogen sulfide gas are produced.
- During the reduction form +6 to -2, the sulfur passes through oxidation state 0 and so some yellow, solid sulfur may be seen.
What is a disproportionation reaction
A type of REDOX reaction where the oxidation state of some atoms of the same elements increase and others decrease.
Describe how chlorine reacts with water
Chlorine reacts with water in a reversible reaction to form chloric(I) acid, HClO, and hydrochloric acid, HCl.
Explain why the reaction of chlorine with water is a disproportionation reaction
- The oxidation number of one of the chlorine atoms increases from 0 to +1 (HClO)
- The oxidation number of one of the chlorine atoms decreases from 0 to -1 (HCl)
What is the equation for the reaction of chlorine with water
Cl2 + H2O <=> HClO + HCl
What is the equation for the reaction of chlorine with water in the presence of sunlight
2Cl2 + 2H2O —> 4HCl + O2
Why do shallow pools need frequent addition of chlorine
Chlorine is rapidly lost from pool water in sunlight.
What is an alternative method of chlorinating swimming pools (not the direct chlorination)
Adding solid sodium (or calcium) chlorate.
What is the equation for the chlorination of water with solid sodium chlorate
NaClO + H2O <=> Na+ + OH- + HClO
Why are swimming pools kept slightly acidic
- When you chlorinate swimming pools with solid sodium (or calcium) chlorate,if the solution is alkaline, the HClO is removed as Cl- ions as the equilibrium moves to the left.
- Therefore, to stop this, conditions are slightly acidic.
- However, this is carefully monitored and the solution never gets acidic enough to corrode metal components and affect swimmers.
Describe how chlorine reacts with an alkali
- Chorine reacts with cold, dilute sodium hydroxide to form sodium chlorate(I), NaClO.
- This is an oxidising agent and the active ingredient in household bleach.
- This is a disproportionation reaction and the other halogens behave similarly.
