The halogens Flashcards
Why does the atomic radius of the group 7 elements increase down the group?
The greater the atomic number the more electrons there are, these additional electrons go into shells increasingly further from the nucleus
Why does the electronegativity of the group 7 elements decrease down the group?
There is an increasing number of shells so more
shielding and less pull on the outer electrons
There is also an increasing atomic radius so
attraction of nucleus for outer electrons drops off as
the distance increases
Why does the boiling point of group 7 elements increase down the group?
Increased number of electrons in larger atoms, van der waals forces between molecules increase so more energy is required to separate the molecules
What is the trend in oxidising ability of group 7 elements down the group?
it decreases
Why does the oxidising ability of group 7 elements decrease down the group?
The increasing nuclear charge which should attract electrons more is offset by increased shielding and increasing atomic radius
Write a balanced equation with state symbols for the reaction of chlorine with sodium bromide and state the type of reaction
Cl2 (aq) + 2NaBr (aq) → Br2 (aq) + 2NaCl (aq)
Displacement (or redox)
Write a balanced ionic equation for the reaction of bromine with iodide ions
Br2 + 2I¯ → I2 + 2Br¯
What is the trend in the reducing ability of the halide ions down the group?
It increases
Why does the oxidising ability of the halide ions increase down the group?
Down the group it becomes easier to lose an
electron because ions are larger
There is also more shielding (due to extra electron
shell
Write down 2 observations that would be made
when sodium chloride reacts with concentrated
sulfuric acid?
Name the substances responsible for these
observations.
Write a balanced equation showing the formation
of these substances.
White solid - sodium hydrogensulfate, (NaHSO4)
Steamy fumes - hydrogen chloride (HCl)
NaCl + H2SO4 → NaHSO4 + HCl
Write down 4 observations that would be made
when sodium bromide reacts with concentrated
sulfuric acid?
Name the substances responsible for these
observations.
Write 2 balanced equations showing the formation
of these substances.
White solid - sodium hydrogensulfate (NaHSO4)
Steamy fumes - hydrogen bromide (HBr)
Orange/brown fumes - bromine (Br2)
Colourless gas - sulfur dioxide (SO2)
NaBr + H2SO4 → NaHSO4 + HBr
2HBr + H2SO4 → Br2 + 2H2O + SO2
Write down 6 observations that would be made
when sodium iodide reacts with concentrated
sulfuric acid?
Name the substances responsible for these
observations.
Write 4 balanced equations showing the formation
of these substances.
White solid- sodium hydrogensulfate
Steamy fumes- hydrogen iodide
Black/purple fumes- iodine gas
Pungent colourless gas- sulfur dioxide
Pungent colourless gas that smells of rotten eggs- hydrogen sulfide
Yellow solid- sulfur
NaI + H2SO4 → NaHSO4 + HI
• 2HI + H2SO4 → I2 + 2H2O + SO2
• 8HI + H2SO4 → 4I2 + 4H2O + H2S
• 6HI + H2SO4 → 3I2 + 4H2O + S
List the 4 steps for testing an unknown solution for halide ions
- Acidify the solution with dilute nitric acid
- Add a few drops of silver nitrate solution
- Treat any precipitate with dilute ammonia solution
- If a precipitate still exists, add concentrated
ammonia solution
What is the observation for a positive result to
show the presence of:
a) fluoride ions?
b) chloride ions?
c) bromide ions?
d) Iodide ions?
a) No reaction
b) White precipitate that is soluble in dilute ammonia solution
c) Cream precipitate that is insoluble in dilute
ammonia but soluble in concentrated ammonia
solution
d) Yellow precipitate that is insoluble in both dilute
and concentrated ammonia solution
Describe the test for chlorine gas
Damp litmus paper will bleach white if chlorine gas is present
Write a balanced equation with state symbols for the reaction of chlorine with water to form hydrochloric acid and chloric acid
Cl2 (g) + H2O (l) → HCl (aq) + HOCl (aq)
Why is chlorine used in water treatment despite the toxicity of chlorine?
It reacts with water to forming chloric(I) acid (an
oxidising agent) which kills bacteria by oxidation
The benefits to health of water treatment by
chlorine outweigh its toxic effects
Why is the reaction of chlorine with water called a disproportion reaction?
Because chlorine is simultaneously oxidised and reduced
Write a word and balanced reaction with state symbols for the reaction of chlorine it’s cold aqueous sodium hydroxide
sodium hydroxide + chlorine → sodium chloride +
sodium chlorate(I) + water
2NaOH (aq) + Cl2 (g) → NaCl (aq) + NaOCl (aq) + H2O (l)
Explain in terms of the changes in oxidation states why the reaction of chlorine and cold aqueous
sodium hydroxide is an example of a disproportionation reaction
Chlorine changes oxidation states from 0 to -1 and 0 to +1 in
the same reaction
