ES1: Halogens Flashcards
What group are the halogens in?
Group 7
What block are the halogens in?
P block
What electronic configuration do all the halogens have?
ns2np5
Why are halogens not found as elements on their own?
Too reactive
What three ways do halogens exist naturally?
- Exist as ionic compounds
- Exist as separate covalently bonded diatomic molecules
- By sharing an electron from another metal atom
What’s fluorine’s appearance at room temperature?
Pale yellow gas
What’s chlorine’s appearance at room temperature?
Green gas
What’s bromine’s appearance at room temperature?
Dark red liquid
What’s iodine’s appearance at room temperature?
Shiny grey/black solid
What’s chlorine’s appearance in water?
Virtually colourless
What’s bromine’s appearance in water?
Yellow/orange
What’s iodine’s appearance in water?
Brown
What’s chlorine’s appearance in hexane?
Virtually colourless
What’s bromine’s appearance in hexane?
Orange/red
What’s iodine’s appearance in hexane?
Pink/violet
How does the reducing ability of the halogens change down the group?
Increases
How does the oxidising ability of the halogens change down the group?
Decreases
Why does the reducing ability of the halogens increase down the group?(4)
- Increased atomic radius
- Increased electron shells between the nucleus and the outer shell of electrons
- More electron shielding means less of an attraction between the nucleus and the outer shell
- Harder to attract an electron towards it
How does the volatility of the halogens change down the group?
Decreases
What is volatility?
The ease with which an element evaporates into a gas
Why does the volatility of the halogens decrease down the group? (4)
- Increased atomic radius: larger molecule
- Larger electron cloud
- Stronger instantaneous dipole-induced dipole bonds
- Harder to break these strong intermolecular bonds to change state into a gas
How does the electronegativity of the halogens change down the group?
Decreases
How soluble are halogens in water?
Low solubility
Why do halogens have a low solubility in water?
They form covalent and non polar molecules
What substances do halogens dissolve more easily in than water?
Organic solvents e.g hexane
Why is it useful to dissolve halogens in hexane?
They have more distinctive colours when dissolved in hexane so are easier to tell apart
How do halogens react?
By gaining an electron (being reduced) and oxidising another substance
Are halogens stronger oxidising agents or reducing agents?
Oxidising agents
What is the general formula for a halogen reacting?
X + e- ===> X-
What happens in a displacement reaction with halogens?
A more reactive halogen will displace a less reactive halide in a solution
Give the formula for a displacement reaction with chlorine and potassium iodide.
Cl2 (aq) + 2KI(aq) ====> 2KCl (aq) + I2 (aq)
What colour change would you observe in a displacement reaction with chlorine and potassium iodide?
The solution would turn from pale green to brown
How could a clearer colour change be observed in a displacement reaction?
By shaking the solution with hexane
What does chlorine do in a displacement reaction with chlorine and potassium iodide? Give the half equation.
- Chlorine displaces iodine and gets reduced
- Cl2 + 2e- ====> 2Cl-
What does iodine do in a displacement reaction with chlorine and potassium iodide? Give the half equation.
- Iodine is displaced by chlorine and gets oxidised
- 2I-====> I2 + 2e-
How do you write an ionic equation?
Cancel out the unchanged ions
What reacts with halide ions to form a precipitate?
Silver ions
Give the general formula of a precipitation reaction with silver ions and halide ions.
Ag+ (aq) + X- (aq) ====> AgX(s)
How do you test for halides? (2)
- Add dilute nitric acid
- Add silver nitrate solution
Why do you add dilute nitric acid when testing for halides?
To remove other ions that could interfere in the reaction
What colour precipitate forms with fluorine after reacting with silver ions?
No precipitate forms (trick question :-P)
What colour precipitate forms with chlorine after reacting with silver ions?
White
What colour precipitate forms with bromine after reacting with silver ions?
Cream
What colour precipitate forms with iodine after reacting with silver ions?
Yellow
How do you further distinguish between the silver halides?
By adding ammonia solutions of different concentrations
What happens when you add ammonia solution to AgCl?
Dissolves in dilute ammonia solution to form a colourless solution
What happens when you add ammonia solution to AgBr? (2)
- Does not dissolve in dilute ammonia solution
- Dissolves in concentrated ammonia solution to form a colourless solution
What happens when you add ammonia solution to AgI?
Never dissolves
