Group 7- The Halogens

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  • Created by: Heather
  • Created on: 08-03-15 16:05
What are the first four halogens?
Flourine, Chlorine, Bromine and iodine
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How do the elements exist/ are structured?
As diatomic molecules e.g. F2
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What is the trend of appearance of the gaseous halogens?
They get darker and denser as we go down group 2.
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What is the state and colour of flourine at room temperature?
Gas, -Pale yellow,
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What is the state and colour of chlorine at room temperature?
-Gas, -Greenish,
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What is the state and colour of bromide at room temperature?
-Liquid, -red-brown,
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What is the state and colour of iodide at room temperature?
-Solid, -Black
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What is their usual smell?
'swimming bath' smell
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Why are many of the properties of flourine untypical?
Due to the weakness of the F-F bond as compared to the rest of the halogens,
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Why is the F-F bond so weak?
As the small size of the flourine atom leads to repulsion between non-bonding electrons as they are so close,
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What is the trend in Group 7 for the size of the atoms and why?
They get bigger as we go down Group 7 as each element has one extra filled main level of electrons as compared to the one above,
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What is the definition of electronegativity?
The measure of the ability of an atom to attract electrons towards itself within a covalent bond,
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What is the trend for electronegativity for Group 7?
The electronegativity decreases as we go down Group 7,
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What are three factors why the electronegativity of halogens decrease down the group?
1)Atomic number, 2)Number of electron shells, 3) Atomic radius
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How does the atomic number of the halogen affect the electronegativity?
The atomic number gives the nucleur charge. As this increases, the attraction for the bonding electron pair in a covalent bond might be expected to increase,
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How does the number of electron shells of halogens affect the electronegativity?
As this number increase, the shielding of the outer electrons from attraction by the nucleus increases,
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How does the atomic radius of the halogen affect the electronegativity?
As the radius of the arom increases, the outer electrons are further from the nucleus which therefore attracts them less strongly,
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What is the trend for melting and boiling points of Group 7 halogens?
They increase as we go down the group,
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Why does the melting/boiling point of halogens increase as we go down Group 7?
As the larger atoms have more electrons and this makes the van der Waals forces between the molecules stronger.
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The lower the boiling point the more _ _ _ _ _ _ _ _ the element.
volatile
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Describe the oxidising ability of halogens?
The oxidising ability of the halogens decrease as we go down Group 7,
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Which element is the most powerful oxidising agent?
Flourine
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What is the definition of a displacement reaction?
A chemical reaction in which one atom or group of atoms replaces another in a compound
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Describe a displacement reaction involving halogens?
Halogens will react with metal halides in solution in such a way that the halide will be displaced by a more reactive halogen
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What is the equation to show the chlorine displacing metal(M) bromide?
Cl2(aq) + 2MBr(aq) -> Br2(aq) + 2MCl(aq)
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What is the ionic equation for this reaction?
Cl2(aq) + 2Br-(aq) -> Br2(aq) + 2Cl-(aq)
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Why were the metal(M) ions not included in this equation?
As they are spectator ions,
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In the reaction, which element/compound was the oxidising agent and why?
Chlorine- As it removed the electrons from 2Br- to Br2,
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Why cant flourine be investigated in aqueous solution?
As it reacts with water due to its strong oxidising power.
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What is an example of the oxidation of a halide by a halogen in everyday life?
The extraction of bromine from the sea,
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Write the equation to show how bromide ions are oxidised by chlorine?
Cl2(aq) + 2Br-(aq) -> Br2(aq) + 2Cl-(aq)
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How is bromine liberated from the water?
By using air and is then concentrated in a series of stages,
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Give the trend for the reducing power of halogens?
The reducing power of the halogens increase as we go down the group,
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Why does the reducing power of halogens decrease as we go down Group 7?
As the larger the ion, the more easily it loses an electron. This is becuase the electron is lost from the outer shell which is further from the nucleus as the ion gets larger,
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Which ion has the largest reducing power?
I-, Iodide,
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What states are sodium chloride, sodium bromide and sodium iodide?
solid
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When a sodium halogen reacts with concentrated sulfuric acid, what is alway produced and observed?
Hydrogen X which produces steamy fumes,
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Give the equation for the reaction between sodium chloride and concentrated sulfuric acid?
NaCl(s) + H2SO4(l) ->NaHSO4(s) + HCl(g)
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What is observed during this reaction?
Streamy fumes from the hydrogen chloride and a precipitate of sodium hydrogensulfate,
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WHy is this equation/reaction not a redox reaction?
As the oxidation states have not changed as the chloride ion is too weak as a reducing agent to reduce sulfur,
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What type of reaction is this?
An acid-base reaction so neutralisation,
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Give the equation for the reaction between sodium bromide and concentrated sulfuric acid?
NaBr(s) + H2SO4(l) -> NaHSO4(s) + HBr(g)
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What is observed during this reaction?
-Steamy fumes of hydrogen bromide and brown fumes of bromide, -Colourless sulfur dioxide
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Is bromide ions strong enough reducing agents to reduce the sulfuric acid?
Yes
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Give the ionic equation for the reduction of the products formed in the first equation?
2H+ + 2Br- +H2SO4(l) -> SO2(g) + 2H20(l) + Br2(l)
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Why is this a redox reaction?
As the bromide is oxidised from -1 to 0 and sulfur is reduced from +6 to +4
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Give the equation for the reaction between sodium iodide and concentrated sulfuric acid.
NaI(s) + H2SO4(l) ->NaHSO4(s) + HI(g)
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What is observed during this reaction?
-Steamy fuems of hydrogen iodide, -Black solid of iodide,
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Iodide ions are better reducing agents than bromide. Give three products it can form alternatively from NaHSO4 and what is observed with the formation of each?
-S or sulfur-Yellow solid,e -SO2 or sulfur dioxide-Colourless gas, -H2S or hydrogen sulfide-Bad egg smell
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Give the equation to show the reduction of the products of the first equation into hydrogen sulfide
8H+ + 8I- + H2SO4(l) -> H2S(g) + 4H2O(l) +4I2(s)
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How can you identify metal halides except flourine?
With silver ions in aqeuous solution
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Why cant silver flouride be detected?
As it is soluble in water so a precipitate wont form to show its presence,
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Give the ionic equation for the formation of silver chloride
Cl-(aq) + Ag+(aq) -> AgCl
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What is first added to the halide solution and why?
Dilute nitric acid HNO3 to get rid of any soluble carbonate, CO32-(aq) or hydroxide, OH-(aq) impurities
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Give the equation to show the ionic equation of carbonate reacting with nitric acid
CO32-(aq) + 2H+(aq) +2NO3-(aq) -> CO2(g) + H2O(l) + 2NO3-(aq)
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What would form if the carbonate or hydroxide wasnt removed?
Insoluble silver hydroxide or silver carbonate,
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What is then added after nitric acid?
Silver nitrate solution
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What forms for chloride ions?
A white precipitate
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What happens if dilute ammonia was added?
it would dissolve
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What forms for bromide ions?
A cream precipitate
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What would happen if diulte ammonia was added?
Nothing,
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what is needed for silver bromide to be dissolved?
concentrated ammonia
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What is formed for iodide ions?
A pale yellow precipitate
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Is this precipitate soluble?
No it is insoulbe in concentrated ammonia,
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Give the equation to show chlorine reacting with water.
Cl2(g) + H2O(l) HClO(aq) + HCl(aq)
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What is the definition of a disproportionation reaction?
A redox reaction in which the oxidation numner of some atoms of a particular elemtn increases and that of the other atom of the same element decreases,
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Why is this reaction a disproportionation reaction?
As one of the chlorine atoms increases from 0 to +1 and the other decreases from 0 to -1
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What is this reaction used for?
To purify water for drinking and swimming to prevent diseases
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How do chlorine atoms kill the bacteria?
It is an oxidising agent so kills bacteria by oxidation,
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What form can chlorine atoms take in everyday life?
Bleach
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Rewrite the reaction between chlorine atoms and water in sunlight.
2Cl2 + 2H2O(l) ->4HCl(aq) + O2(g)
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What is an alternative to adding chlorine atoms?
Sodium (or calcium) chlorate or NaClO
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How is NaClO formed?
When chlorine reacts with cold, dilute sodium hydroxide,
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For a reaction with Cl2 (aq), what observations are made when it reacts with Br-(aq) and why?
Yellow/brown solution formed as the Br2 has been displaced,
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Give the ionic equation for the displacement reaction between bromide ions and chlorine?
2Br- + Cl2 -> 2Cl- + Br2
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For the reaction with Cl2 (aq), what observations are made when it reacts with I- (aq) and why?
A brown solution and/pr black precipitate as the I2 has been displaced,
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Give the ionic equation for this displacement reaction?
2I- + Cl2 -> 2Cl- + I2
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For a reaction with Br- (aq), what observations are made when it reacts with Cl- and why?
No change as the Cl2 has not been displaced as it is less reactive,
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For a reaction with Br- (aq), what observations are made when it reacts with I-(aq) and why?
A brown solution and/or black precipitate as I2 has been displaced,
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Give the ionic equation for the displacement reaction between Br2 and I-?
2I- + Br2 -> 2Br- + I2
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For a reaction with I2 (aq), what observations are made when it reacts with Cl-(aq) and why?
Nothing as Cl2 has not been displaced as it is less reactive,
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For a reaction with I2 (aq), what observations are made when it reacts with Br-(aq) and why?
Nothing as Br2 has not been displaced as it is less reactive,
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How do the elements exist/ are structured?

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As diatomic molecules e.g. F2

Card 3

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What is the trend of appearance of the gaseous halogens?

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Card 4

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What is the state and colour of flourine at room temperature?

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Preview of the front of card 4

Card 5

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What is the state and colour of chlorine at room temperature?

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