Chapter 10 - Group 7, The Halogens Flashcards
What are the trends in electronegativity as you go down the group? Why?
They become less electronegative because in a covalent bond the positive nucleus becomes further away from the valent electrons, so they exert less attractive forces than the nucleus of fluorine for example
What are the trends in boiling point? Why?
The lower down the group you go the higher the boiling point because you gain an extra shell of electrons each time, and more electrons means more chance for Van Der Waals to be formed and increased inter molecular forces will increase the boiling point.
What is the trend in oxidising ability of the halogens? Why? What does this mean for halide compounds?
They become weaker oxidising agents as you go down the group because the nucleus becomes more and more shielded and further away from the electrons in the reducing agent, therefore it makes it harder for it to oxidise. This means that halide ions in a compound with a cation will always be displaced by a halogen from a higher period, fluorine is never displaced by another halogen.
What gives fluroine the characteristics which are very untypical of the rest of the group?
The F - F bond is extremely unstable and therefore extremely easy to break (requiring little activation energy) due to the proximity of the fluorine atoms due to their size, there is a lot of repulsion between the electrons.
Explain the trend in reducing ability of the halides:
They halide ions become stronger reducing agents as you go down the group, i.e. iodine gives up its electron very easily due to it being so far away from the nucleus and being shielded by so many other shells of electrons
What does this mean for the reactions with Sulfuric acid(l)
Sodium Chloride(s): Acid-base reaction to form sodium hydrogen sulfate and hydrogen chloride gas (steamy white fumes observed), the chloride ion is too weak to reduce the sulfate ion, this is the same reaction as a fluoride ion
Sodium Bromide(s): The same reaction will occur as before, however bromide can reduce the Sulfur from +6 to +4 and form sulfur dioxide in an exothermic reaction. Steamy white fumes will still be observed as well as brown bromine fumes
Sodium iodide(s): The same reactions will occur as before with the same observations (black fumes instead of brown) however iodide ions can reduce the sulfur to both 0 and -2 states as well, resulting in solid yellow sulfur and the rotten egg smell of hydrogen sulfide
Silver Halide test procedure and why:
Begin by adding nitric acid to the solution to remove any hydroxide and carbonate ions, because both of them would bond to the silver and cause a false positive. In both reactions the nitrate ion essentially acts as a catalyst for the proton. then add the silver nitrate solution to the acidified test sample.
Results of the silver halide test:
Chlorine - white ppt which is easily soluble in silute ammonia
Bromine - cream ppt which is only soluble in concentrated ammonia
Iodine - pale yellow ppt which is insoluble in ammonia
Why is chlorine used in pools and how does it work?
It is soluble in water in a disproportionation reaction to form chloric(I) acid, an oxidising agent which kills bacteria. However in U.V it instead only forms hydrochloric acid in a one way reaction as opposed to its usual reversible reaction
What is bleach?
Bleach is when chlorine has been reacted with an alkaline, e.g NaOH to form NaClO, which can also be added to water to form chloric(I) acid again. The formation of bleach is another example of a disproportionation reaction
