Group 7, the halogens

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  • Created by: r98
  • Created on: 06-04-16 10:38
What does the word halogen mean?
'salt former'. The halogens readily react with many metals to form fluoride, chloride, bromide and iodide salts.
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Where is Group 7 situated on the periodic table? What is it made up of?
On the right-hand side. It's made up of non-metals.
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How can we describe the elements of Group 7? What do we call them?
As elements they exist as diatomic molecules, F2,Cl2, Br2, I2 and At2, called halogens.
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At room temperature, what is the state and colour of fluorine?
It's a pale yellow gas.
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At room temperature, what is the state and colour of chlorine?
It's a greenish gas.
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At room temperature, what is the state and colour of bromine?
It's a red-brown liquid.
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At room temperature, what is the state and colour of iodine?
It's a black solid.
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Why is the F-F bond unexpecctedly weak?
The small size of the fluorine atom leads to repulsion between non-bonding electrons because they're so close together.
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Do the atoms get bigger or smaller as you go down the group? Why/
The atoms get bigger as you go down the group because each element has one extra filled main level of electrons compared with the one above it.
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What is electronegativity a measure of?
It's a measure of the ability of an atom to attract electrons, or electron density, towards itself within a covalent bond.
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What does electronegativity depend on?
The attraction between the nucleus and bonding electrons in the outer shell. This, in turn, depends on a balance between the number of protons in the nucleus (nuclear charge) and the distance between nucleus and the bonding electrons, plus shieldng.
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Does electronegativity increase or decrease as you go down the group?
Electronegativity decreases as you go down the group.
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Melting and boiling points involve weaking & breaking what forces?
van der Waals forces only. The covalent bonds in the halogen molecule stay intact.
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Do melting and boiling points increase or decrease as you go down the group?
Increase as you go down the group, because the larger atoms have more electrons & this makes the vdW forces between the molecules stronger.
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What can be said about how volatile an element is by referring to its boiling point?
The lower the boiling point, the more volatile the element. E.g. chlorine (a gas at room temp) is more volatile than iodine (a solid).
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When halogen react, do they usually become positive or negative ions? What charge is on the ion?
They usually react by gaining electrons to become negative ions, with a charge of -1.
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Are the reactions involving halogens redox reactions? If so, what role does the halogen play?
Yes they're redox reactions; halogens are oxidising agents and are themselves reduced.
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The the oxidising ability of a halogen increase or decrease as you go down the group?
Decreases as you go down the group.
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Which halogen is the most powerful oxidising agent?
Fluorine.
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What is a displacement reaction, in reference to halogens?
Halogens will react with metal halides in solution, in a way that the halide in the compound will be displaced by a more reactive halogen (but not by a less reactive one).
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What's the general rule of halogens displacing one another?
In general, a halogen will always displace the ion of a halogen below it in the periodic table.
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What halide ions will chlorine displace?
Br- & I-.
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What halide ions will bromine displace?
I-.
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Will iodine displace the halides F-, or Cl-, or Br-?
No, it does not displace any of these ions.
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What halide ions will fluorine displace? What is the problem with investigating fluorine in aqueous solution?
Cl-, Br- and I-. But we can't investigate fluorine in aqueous solution because it reacts with water.
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What colour change (of solution) would be observed if chlorine and sodium bromide reacted?
Two colourless solutions (Cl2 & NaBr) would react to produce a red-brown solution (bromine).
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Can halide ions act as reducing agents?
Yes, in these reactions the halide ions lose electrons.
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What do halide ion become when they lose electrons?
They become halogen molecules.
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What is the trend in reducing ability of halide ions as you go down Group 7?
Their reducing power increases as you go down the group.
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How is the trend, of reducing ability, linked to atomic radius?
The larger the ion, the more easily it loses an electron. This is because the electron is lost from the outer shell which is further from the nucleus as the ion gets larger.
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Is the reaction between sodium chloride and concentrated sulfuric acid a redox reaction? If not, why not?
No, because no oxidation state has changed. The chloride ion is too weak a reducing agent to reduce the sulfur, in sulfuric acid. It's an acid-base reaction.
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What is formed when drops of concentrated sulfuric acid are added to solid sodium chloride?
Steamy fumes of hydrogen chloride are seen & the solid product is sodium hydrogensulfate.
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What reaction occurs between sodium chloride and concentrated sulfuric acid?
NaCl(s) + H2SO4(l) -----> NaHSO4(s) + HCl(g)
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What gas is produced when sodium fluoride reacts with concentrated sulfuric acid?
Hydrogen fluoride.
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What fumes are produced when sodium bromide reacts with concentrated sulfuric acid?
Steamy fumes of hydrogen bromide, brown fumes of bromine & colourless sulfur dioxide.
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What is the equation for the acid-base reaction that occurs between soduim bromide and conc. sulfuric acid?
NaBr(s) + H2SO4(l) -----> NaHSO4(s) + HBr(g)
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What do bromide ions reduce sulfuric acid to? What happens to the oxidation state of sulfur during this reaction?
Sulfur dioxide. The oxidation state of sulfur is reduced from +6 to +4.
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What name is given to the type of reaction that occurs between the bromide ions and the conc. sulfuric acid? What happens to the oxidation state of the bromide ions during this reaction?
Redox reaction. The oxidation state of the bromine increases from -1 to 0.
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What's the equation for the redox reaction that takes place between bromide ions and conc. sulfuric acid?
2H+ + 2Br- + H2SO4(l) -----> SO2(g) + 2H2O(l) + Br2(l)
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Is the reaction between bromide ions and conc. sulfuric acid endothermid or exothermic?
The reaction's exothermic.
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What can be observed when sodium iodide reacts with conc. sulfuric acid?
We see steamy fumes of hydrogen iodide, black solid iodine, bad egg smell of hydrogen sulfide gas, yelliw solid sulfur, and colourless sulfur dioxide is also evolved.
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What's the equation of the acid-base reaction between sodium iodide and conc. sulfuric acid, in which hydrogen iodide is produced?
NaI(s) + H2SO4(l) -----> NaHSO4(s) + HI(g)
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Are iodid ions better reducing agents than bromide ions? What do they reduce sulfur (in sulfuric acid) to? What's produced?
Iodide ions are better reducing agents than bromide ions, they reduce the sulfur from +6 to 0 and -2. Sulfur dioxide, sulfur and hydrogen sulfide gas are produced.
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What's the equation between iodide ions and conc. sulfuric acid?
8H+ + 8I- + H2SO4(l) -----> H2S(g) + 4H2O(l) + 4I2(s)
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Which metal halides react with silver ions, in aqueous solution?
All metal halides, except fluorides.
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What precipitates are formed when metal halides react with silver ions? What is exception to this?
A precipitate of insoluble silver halide. Silver fluoride doesn't form a ppte because it's soluble in water.
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What would the equation be, if chloride ions reacted with silver ions?
Cl-(aq) + Ag+(aq) -----> AgCl(s)
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What is the formula for nitric acid? Why is dilute nitric acid first added to the halide solution?
HNO3 first added to get rid of any soluble carbonate, CO3^(2-)(aq), or hydroxide OH-(aq) impurities.
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What's the equation for the reaction between nitric acid and carbonate ions?
CO3^(2-)(aq) + 2H+ + 2NO3-(aq) -----> CO2(g) + H2O(l) + 2NO3-(aq)
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What's the equation for the reaction between nitric acid and hydroxide ions?
OH-(aq) + H+(aq) + NO3-(aq) -----> H2O(l) + NO3-(aq)
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What's the equation for the formation of silver carbonate?
2Ag+(aq) + CO3^(2-)(aq) -----> Ag2CO3(s)
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What's the equation for the formation of silver hydroxide?
Ag+(aq) + OH-(aq) -----> AgOH(s)
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After the impurities have been removed, what is added to the halide solution? What is formed?
A few drops of silver nitrate solution (AgNO3) are added and the halide precipitate is formed.
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Since the colours of silver bromide and silver iodide are similar, how can we distinguish between the two?
Add a few drops of concentrated ammonia solution, silver bromide dissolves but silver iodide doesn't.
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What colour precipitate is formed if the halide is silver fluoride?
No precipitate.
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What colour precipitate is formed if the halide is silver chloride? What further test could be done on this solution? Would the ppte dissolve?
White precipitate. Add dilute ammonia, ppte will dissolve.
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What colour precipitate is formed if the halide is silver bromide? What further test could be done on this solution? Would the ppte dissolve?
Cream precipitate. Add conc ammonia, ppte will dissolve.
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What colour precipitate is formed if the halide is silver iodide? What further test could be done on this solution? Would the ppte dissolve?
Pale yellow precipitate. Add conc ammonia, ppte will not dissolve (insoluble in ammonia).
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What is formed when chlorine reacts with water?
chloric(I) acid anf hydrochloric acid.
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What's the equation for the reaction between chlorine and water?
Cl2(g) + H2O(l) -----> HClO(aq) + HCl(aq)
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What type of redox reaction is the reaction between chlorine and water? Why is it called this?
Disproportionation reaction. The oxidation state of some atoms of the same element increase and others decrease; one chlorine atom increases from 0 to +1, and the other decreases from 0 to -1.
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What is the reaction of chlorine with water used for?
To purify water, chloric(I) acid is an oxidising agent and kills bacteria by oxidation. It's also a bleach.
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What's the equation for the reaction between chlorine and sunlight?
2Cl2(g) + 2H2O(l) -----> 4HCl(aq) + O2(g)
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What's an alternative to direct chlorination of swimming pools?
Add solid sodium (or calcium) chlorate(I).
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What's the equation for the reversible reaction between solid sodium carbonate chlorate(I) and water?
NaClO(s) + H2O(l) -----> Na+(aq) + OH-(aq) + HClO(aq)
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Why are swimming pools kept slightly acidic?
Because in alkaline solution, the equilibrium moves left and the HClO is removed as ClO- ions.
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What's the equation for the reaction between chlorine and cold, dilute sodium hydroxide?
Cl2(g) + 2NaOH(aq) -----> NaClO(aq) + NaCl(aq) + H2O(l)
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What is the common use of the sodium chlorate(I), NaClO?
It's an oxidising agent and is the active ingredient in household bleach.
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