Group 7 (Halogens)
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How does the appearance of the halogens change going down the group?
they become darker and denser
Why are many of the properties fluorine considered untypical?
• The F-F bond is weaker than expected • This is because the F atoms are smaller and there is repulsion between non-bonding electrons
Describe and explain the trend in electronegativity going down the group
Electronegativity decreases, as the atoms get larger and electron shielding increases therefore the electrostatic attraction between the nucleus and electrons decreases.
Describe and explain the trend in boiling points down the group
Boiling points increase as the atoms get larger and have more electrons so the VDWs forces get stronger
How does the oxidising ability of the halogens change going down the group?
It will decrease going down the group
What happens in a displacement reaction?
Halogens react with metal halides in a solution in such a way that the halide in the compound will be displaced by a more reactive halogen
How does the reducing power of the halogens change going down the group?
The halides become more reducing as you go down the group. The larger the ion, the more easily it can give away an electron
What is the simplest ionic equation for the reaction of solid NaCl with concentrated sulfuric acid? What is an observation of this reaction?
Cl- + H2SO4 –> HCl + HSO4- Steamy,white fumes, turns litmus paper red
What is the simplest ionic equation for the reaction of solid NaBr with concentrated sulfuric acid? What is an observation of this reaction?
2Br- + H2SO4 + 2H+ –> Br2 + SO2 + 2H2O Orange vapour and choking gas
What are the ionic equations for the reaction of solid NaI with concentrated sulfuric acid? What are the observations of these reactions?
6I- + H2SO4 + 8H+ –> 3I2 + S + 4H2O yellow solid produced and purple vapour 8I- + H2SO4 + 8H+ –> 4I2 + H2S + 4H2O foul smelling gas and purple vapour
The reaction of Cl and water is an example of what type of reaction?
disproportionation
What is a disproportionation reaction?
A reaction where an element is being both reduced and oxidised.
When using ammonia to test for Cl- ions, what is the expected result?
The ppt. will dissolve in dilute ammonia
When using ammonia to test for Br- ions, what is the expected result?
The ppt. will dissolve in concentrated ammonia
When using ammonia to test for I- ions, what is the expected result?
the ppt will not dissolve
Give the equation for the reaction of chlorine with cold water
Cl2 + H2O -> HClO + HCl
Give the equation of chlorine with water in the presence of UV light
2Cl2 + 2H2O -> 4HCl + O2
What is a benefit of using Chlorine in water sterilisation?
kills potentially harmful microorganisms stopping disease
What is a risk of using Chlorine in water sterilisation?
• Cl2 gas is toxic • can increase risk of cancer if react with hydrocarbons • can cause allergic reactions
Give the equation showing the reaction of chlorine with cold, dilute sodium hydroxide
Cl2 + 2NaOH -> NaClO + NaCl + H2O
What is a use of NaClO?
active ingredient in household bleach