Chemistry- Unit 2- Group 7, the halogens

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  • Created by: FireDwarf
  • Created on: 08-02-14 16:04
What group are the halogens?
Group 7
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Physical Properties of F? (Colour & state), Cl, Br, I
Pale Yellow Gas, Green gas, red-brown liquid, black solid
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What is special about the F-F bond?
Unusually weak compared to the trend of the other halogens.
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Trend of eletronegatvity in halogens? Why?
Increases up the group- Less shielding, increases the ability for positive nucleus to attract bonded electrons, which increases its pull, increasing electronegativty.
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Size of the atom?
Increases down the group - more shielding.
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Melting & boiling points?
Increase down the group- More shielding and therefore more electrons- more Van der waals- more intermoleuclar attraction- more energy needed to break molecules apart.
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What are halogens in regards to oxidising & reducing? How does their ability increase & why?
They are oxidising agents , increases up group, less shielding, increased ability to attract electrons to itsself, causes other to be oxidised therefore.
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What are reducing agents? Trend & why?
Halides, increases down the group. Increased shielding and therefore easier to lose electron due to reduced attraction. Itsself becomes oxidised and other reduced.
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How does a displacement reaction occur with Halogens and Halides?
If the halogen is more reactive then the halide, it will displace the halide from its spectator ions eg: Cl2 + NaBr --> Br2 + NaCl
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How is it shown as an ionic equation?
Cl2 + 2Br- -->2 Cl- + Br2
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How do the colours we observe work?
Colour of whatever has been displaced (eg: the Br2 in the example above).
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Describe how a displacement reactions occurs in terms of oxidisation?
The halogen has acted as an oxidising agent. This therefore oxidises the Br- & causes it to lose electrons. The halogen gains them to become reduced.
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What are the 3 steps to identify a metal halide?
Add nitric acid, add silver nitrate & then add ammonia of diffrent concentrations
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Why add nitric acid?
To get rid of any carbonates or hydroxides
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Because these form insoluble silver carbonates & silver hydroxides which would intefere with the formation of the silver halides.
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Why do we add silver nitrate?
Because this forms a silver halide precipitrate (with the exception of F) which allows us to identify them
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Ag + + Cl- --> AgCl
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What do we add next?
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Colours of precipitate?
F- None, Cl, White, Br, Cream, I - Yellow
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Ammonia reactions?
Adding dilute ammonia causes AgCl to dissolve but not the others. Adding concentrated causes AgCl to dissolve but not AgI. AgI does not dissolve in ammonia at all.
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Equation for Chlorine reacting in water?
Cl2 + H20 (reverisble) HCLO + HCL (Chloric acid + Hydrochloric acid
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What is this reaction called? Why?
Disproportiation- Oxidisation state from some atoms of the same element increase and others decrease.
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Why does this reaction take place?
To purify water. Chloric acid is a oxisising agent and thus kills bacteria.
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What is the reaction when chlorine reacts in sunlight?
2cl2 + 2h20 --> 4HCL + O2
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Why is this bad?
Chlorine is rapidly lost, high HCL conc.
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Alternative because of the sunlight reaction?
Add sodium chlorate (solid)
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Easier to store, not a poisionous gas.
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NaClo + H2o Na + OH + HCLO
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The HCLO is removed as CLO- ions. To prevent this happening, conditions must be slightly acidic BUT NOT TOO MUCH.
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Reactions with alkali?
Cl2 + NaoH --> NACLO + NaCl + H20 (NaClo = bleach)
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Whats going to be reacting in the following equations?
Concentrated sulfuric acid & solid sodium halide (halide salts)
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Sodium chloride equation?
NaCl(s) + H2S04(l) ---> HCL(g) + NahSo4(s)
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What do we observe?
Steamy fumes of hydrogen chloride.
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What do we produce?
Sodium hydrogensulfate.
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Is this redox or not? Why? What is it instead?
No, because the oxidation states have not changed. Chlorine is therefore a weak reducing agent. Acid-base reaction.
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What does it produce which is useful?
hydrogen chloride gas.
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Simular reaction? Product?
Fluorine, even weaker agent. Creates hydrogen fluoride however which is a dangerous gas which etches gas.
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Sodium bromide equation? (1) Observe?
NaBr(s) + H2so4(l) ---> NaHso4(s) + HBr(g) HBr- Mistry fumes
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Second equation?
2H+ + 2Br- + H2So4(l) ---> SO2(g) + 2H20(l) + Br2(l)
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What would you observe?
So2- Chocking colourless gas, brown/organge vapour Br2.
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Sodium iodide equation (1)?
NaI(s) + H2So4(l) ---> NaHSo4(s) + HI(g)
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8H+ + 8I- + H2so4(l) ---> H2s(g) + 4H20(l) + 4I2(s)
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Rotten eggs H2S, black solid (I2) OR can get purple gas if I2 in gas form.
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Other products?
So2 & S - So2 is a chocking colourless gas & sulfur is a yellow solid.
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Card 2


Physical Properties of F? (Colour & state), Cl, Br, I


Pale Yellow Gas, Green gas, red-brown liquid, black solid

Card 3


What is special about the F-F bond?


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Card 4


Trend of eletronegatvity in halogens? Why?


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Card 5


Size of the atom?


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