10.1 - 10.4 - Group 7 Flashcards
Which Group 7 element does not follow most trends and why?
Fluorine:
- F-F bond very weak compared to the rest of the halogens
- Small size of fluorine = repulsion between non-bonding electrons since they are so close
Describe the atomic radius trend in Group 7
Increases down the group:
- More electron shells
- So bigger atoms
Describe the electronegativity trend in Group 7
Decreases down the group:
- Bigger atoms
- More shielding
- Weaker attraction between nucleus and the 2 electrons in the covalent bond
Describe the boiling point trend in Group 7
Increases down the group:
- All simple covalent molecules
- Bigger molecules = More VdW = higher b.p
Describe the first ionisation energy trend in Group 7
Decreases down the group:
- Atoms get bigger
- More shielding
- Therefore weaker attraction from nucleus to electron in outer shell
Describe the trend in reducing power in Group 7
Increases down the group:
- More shells
- More shielding
- Outer electrons further away
- Easier to lose electrons
Describe the reaction of sodium chloride and sodium fluoride and sulphuric acid
Steamy fumes of HCL/HF gas
It is an acid base reaction
NaCl + H₂SO₄ → NaHSO₄ + HCl (or replace Cl with F)
Describe the reaction of sodium bromide and sulphuric acid
- Steamy fumes of HBr gas and brown fumes of Bromine
Acid-base reaction:
NaBr + H₂SO₄ → NaHSO₄ + HBr
Exothermic redox reaction:
2H⁺ + 2Br⁻ + H₂SO₄ → SO₂ + 2H₂O + Br₂
Overall:
2H2SO4 + 2NaBr → Na2SO4 + SO2 + Br2 + 2H2O
Describe the reaction of sodium iodide and sulphuric acid
- Steamy fumes of hydrogen iodide
- Black sold iodide
- Bad egg smell of hydrogen sulphide gas
Acid-base reaction:
NaI + H₂SO₄ → NaHSO₄ + HI
Redox reaction:
8H⁺ + 8I⁻ + H₂SO₄ → H₂S + 4H₂O + 4I₂
Describe how to test halide ions
Add silver nitrate and nitric acid
Describe the result of the halide ions test
Cl⁻:
- White precipitate (AgCl)
- Precipitate dissolves in dilute NH₃
- Precipitate dissolves in concentrated NH₃
Br⁻:
- Cream precipitate (AgBr)
- Precipitate does not dissolve in dilute NH₃
- Precipitate dissolves in concentrated NH₃
I⁻:
- Yellow precipitate (AgI)
- Precipitate does not dissolve in dilute NH₃
- Precipitate does not dissolve in concentrated NH₃
Describe the reaction of chlorine with cold water
Cl₂ + H₂O ⇌ ClO⁻ + Cl⁻ + 2H⁺
Cl2 + H2O ⇌ HClO + HCl
This is a disproportionation reaction and produces chlorate and chloride ions
Describe the reaction of chlorine with cold water, in the presence of UV light
2Cl₂ + 2H₂O → 4HCl + O₂
Chlorine is used in small quantities in water treatment. The risk or chlorine being toxic is outweighed by the benefits of safe water.
Describe the reaction of chlorine with cold, aqueous sodium hydroxide
2NaOH + Cl₂ → NaClO + NaCl + H₂O
This produces sodium hypochlorite/sodium chlorate(I) which is a key ingredient in bleach
Describe the test for sulphate ions (SO₄²⁻)
- Test with BaCl₂
- Sulphate react to form a white precipitate
Describe the test for hydroxide ions (OH⁻)
- Test with red litmus paper (red -> blue)
- Or test with universal indicator (colourless -> blue/purple)
Describe the test for carbonate ions (CO₃²⁻)
- Test with acid (i.e HCl)
- Carbonate ions will effervesce
- Test these bubbles are CO₂ by bubbling through lime water (colourless -> cloudy)
Describe the test for group 2 ions
Flame tests:
Calcium (Ca²⁺) = Brick red
Strontium (Sr²⁺) = Red
Barium (Ba²⁺) = Pale green
Describe the test for ammonium ions (NH₄⁺)
- Ammonium ions give off ammonia gas (add NaOH to produce gas faster)
- Test by holding red litmus paper over test tube (red -> blue)
Give the ionic equation for AgCl being dissolved in dilute NH3
AgCl(s) + 2NH3(aq) → Ag(NH3)2 + (aq) + Cl−(aq)
Why is nitric acid used when testing for halides?
Removes hydroxide/carbonate ions that may give other ppts with silver nitrate
