Group 7 Halogens Flashcards
Give some properties of the halogens
Have 7 electrons in their outer shell and are in the P block.
Generally diatomic
Have different appearances at room temperature
Have low melting and boiling point as only weak intermolecular forces exist (van der waals)
What is the changes of state that occur down the group and what are their appearances (colour) for each element?
F2 - gas (yellow)
Cl2 - gas (green)
Br2 - liquid ( orangey browny red)
I2 - solid (black)
At2 - solid
What happens to the atomic size of the halogens down the group?
Increases down the group
Due to more electrons in the shells and therefore there are more shells so the atomic radius increase
What is the trend in electronegativity down the group?
Decreases down the group
More electron shells and therefor increased shielding between the outer electrons and the central nucleus by the inner electron shells
This means the outer electrons have less attractive forces acting upon them and are therefore more easily lost
What is the trend in boiling point down the group?
Increases down the group
Each element has an extra shell of electrons and therefore a larger atomic radius
His means there is a greater surface area for a greater abundance of van der waals forces of attraction to act between so the boiling point increases as more energy is required to break the abundance of van der waals
What is the trend in reactivity of the halogens down the group?
Halogens are very reactive
Highly electronegative elements which only require 1 extra electron to obtain a full outer shell.
Down the group reactivity decreases as there are more shells and therefore increased shielding. This means there is less attraction between the positive nucleus and the negative surrounding electrons so fewer electrons are gained producing the full octect outer shell.
Why are halogens strong oxidising agents?
They themselves can easily be reduced by accepting an electron and hence will oxidise another species
What type of ions do the halogens produce?
Halide ions
Cl-
Br-
What is a displacement reaction?
Where a more reactive species will displace a less reactive species from a solution
What is disproportionation?
A disproportionation reaction is one where the same species is both oxidised and reduced in the same reaction
What happens when chlorine is added to water?
Chlorine can dissolve in water to produce HCL or HClO ( products of this reaction can be used to kill bacteria and is used to sanitise water)
What happens when chlorine is added to an alkali?
With cold alkali ( eg NaOH) chlorine will react producing NaCl or NaClO
These can be used as disinfectant or bleaching agents and weed killers
What are the advantages and disadvantages of using chlorine disproportionation properties?
Advantages:
Can be used to sanities water
Prevents the spread of infections (especially water born diseases)
Disadvantages:
Water is chlorinated without direct consent
Chlorine could react with organic matter forming chlorinated hydrocarbons
( could cause cancer)
What happens in the trends of oxidation and reduction for halogens and Halide ions down the group?
Halogens are oxidising agents
Halide ions are reducing agents
Down the group
Oxidising power of halogens decreases
Reducing power of halide ions increases
What happens when halide ions react with conc sulphuric acid?
Halide ions are reducing agents
Sulphuric acid is an oxidising agent
Three possible reactions:
Produce sulphuric dioxide
Produce sulphur
Produce hydrogen sulphide
What happens when chloride ions react with sulphuric acid?
Chloride is a weak reducing agent and so no redox reactions occur between NaCl and H2SO4
Sulphuric acid will donate a proton creating HCL white misty copious white fumes
What happens when bromide ions react with sulphuric acid?
Sulphuric acid acts as an acid donating a proton:
2NaBr + H2SO4 ——> Na2SO4 + HBr
Bromide can reduce sulphuric acid to form sulphur dioxide and water:
HBr + H2SO4 ——> Br2 +SO2 + 2H2O
What happens which iodide ions react with sulphuric acid?
Sulphuric acid acts as an acid:
2NaI + H2SO4 ——> Na2SO4 + 2HI
Iodide can reduce sulphuric acid further to sulphur:
6HI + H2SO4 ——> 4H2O + S + 3I2
Then To hydrogen sulphide:
8H+ + 8I- + H2SO4 ——> 4H2O + H2S + 4I2
What happens when hydrogen halides react with ammonia?
Forms salts of ammonium
What happens when hydrogen halides react with water?
Forms acidic colourless solutions
What is the test for carbonate ions?
- Add aqueous acid to suspected solution
- Is positive then CO2 gas will be produced
- Test the gas by bubbling through limewater and this turns cloudy with CO2
What is the test for sulphate ions?
- Acidify the test solution with drops of HCL (removes carbonate ions as CO2)
- Add a few drops of barium chloride
- If positive a white precipitate forms
What is the test for ammonium ions?
- Add sodium hydroxide to test solution
- Warm the mixture
- Test the gas evolved with damp red litmus paper
- If positive the red litmus will turn blue
What is the test for halide ions?
- Add dilute nitric acid (removes an soluble impurities)
- Add silver nitrate solution
A precipitate of silver halide will form
Each precipitate is a different colour
(Silver fluoride is soluble and so will dissolve in water and cant be detected by this test)
- Add ammonia
As silver bromide and iodide can look similar adding ammonia will help to distinguish between them.
What are the precipitate formed with the halide test?
Silver chloride:
White precipitate
Colourless with ammonia
Silver bromide:
Cream precipitate
Does not dissolve with dilute ammonia
Dissolved to colourless with conc ammonia
Silver iodide:
Pale yellow precipitate
Does not dissolve with ammonia
