3.1.1 GROUP 7, THE HALOGENS Flashcards
Describe and explain the trend in reactivity down group 7
- Reactivity decreases down the
group - Atomic radius increases due to
increased number of shells - Greater shielding between
positive nucleus and an outer
electron, decreasing the
electrostatic attraction felt.
What are the colours of the halogens? (vapours and solid)
Fluorine - colourless/pale yellow
Chlorine - yellow/green
Bromine - Brownish solution
Iodine - grey crystals/ purple vapour
What is the state of each halogen at room temperature?
Fluorine - gas
Chlorine - gas
Bromine - liquid
Iodine - solid
Astatine - solid
General properties of the halogens
- Diatomic
- Toxic
- Volatile
- Simple molecular structures
- Very soluble (in water + other)
- React with aluminium to produce
WHITE TRIHALIDES
What is a commercial use of iodine?
As an antibacterial
What is electronegativity?
The tendency of an atom to attract a bonding pair of electrons in a covalent bond
(Measured with the Pauling scale)
Name the most and least electronegative elements
Most - Fluorine
Least - Francium and Caesium
What is the trend in electronegativity across the periodic table?
Electronegativity increases up groups and along periods
Describe and explain the trend in electronegativity down group 7
- It decreases down the group
- Larger atomic radius, more shells
- Greater shielding
- Weaker attraction between -
positive nucleus and electron pair
Describe and explain the trend in melting and boiling point down group 7
- Increases down the group
- Larger molecules
- Greater van der waals forces
Describe and explain the trend in first ionisation energy down group 7
- Decreases down the group
- Larger atomic radius, more shells
- Greater shielding
- Weaker attraction between outer
electron and positive nucleus - More easily removed
What are the colours of the halogens in organic solvents?
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Write the equations for halogens acting as oxidising agents, and halides acting as reducing agents
X2 + 2e- —— 2X-
^ Oxidising agent
2X- ——- X2 + 2e-
^Reducing agent
How does the oxidising ability of the halogens change down the group?
It decreases
Larger atomic radius, more shells
Greater shielding
Less electrostatic force felt between nucleus and another electron in a compound
Describe how the reducing ability of the halogens change down the group
Reducing ability increases
Greater shielding (Ar + shells)
Less attraction between outer electron and positive nucleus
Easier to lose an electron, as less energy is required to remove it
Why do redox reactions not happen when fluorine and chlorine react with concentrated sulfuric acid?
Fluorine and Chlorine are not strong enough oxidising agents
(instead undergo reaction with H2SO4 as a proton donor)
Write a general form for the (acid) reaction between halide ions and concentrated sulfuric acid
X- + H2SO4 —— HX + NaHSO4
e.g. NaCl + H2SO4 – HCL + NaHSO4
What are the properties of hydrogen halides?
- Colourless gases at room
temperature - Form steamy fumes in moist air
What are the properties of hydrogen sulfide?
- Colourless
- Corrosive
- Flammable
What happens in the reaction between bromide ions and sulfuric acid?
Bromide ions reduce SO4 to SO2, and are oxidised to neutral Br2 molecules, producing water as well
H2SO4 + 2Br- + 2H+ – SO2 + Br2 + 2H2O
State the charge on the hydrogen sulfate ion, and the oxidation numbers on the elements involved
HSO4 [-1]
H + 1
S - 2
O -2
Describe what happens when concentrated sulfuric acid reacts with iodide ions
- Sulfuric acid is reduced from S+6
then to S+4, then to neutral sulfur. - Sulfur is then reduced to -2 in
hydrogen sulfide, if there is
enough iodine to reduce all the
sulfur. - Water is also produced
- Iodine acts as a reducing agent and is oxidised to I2 molecules
What is the overall equation for when concentrated sulfuric acid reacts fully with iodide ions?
H2SO4 + 8I- + 8H+ – 4I2 + H2S + 4H2O
