Halogens Flashcards
(19 cards)
Physical properties of halogens
F- poisonous yellow gas
Cl- poisonous dense green gas
Br- toxic brown volatile liquid, brown vapour
I- black solid, violet vapour (sublimes)
As- never seen enough
Trend in halogens bond enthalpy
Bond enthalpy decreases down group
Except F which has similar bond enthalpy to I due to lone pairs repelling bonding pairs weakening the bond
Trends down group 7
Colours darken
Atomic radius increases
Reactivity decreases
Boiling points increase
Electronegativity decreases
Why does atomic radius of halogens increase
More energy levels of electrons
Outer energy levels further from nucleus
Why does Reactivity decrease down halogens
Outer electrons further away
Increased shielding
Weaker nuclear attraction so less likely to aattract a new electron
Why does boiling points of halogens increase
Diatomic size increases
More electrons involved in van Der waals forces
More energy needed to overcome
Why does electronegativity decrease down halogens
Bonding electrons further from positive nucleus
More shielding
Positive nucleus attracts bonding pair less strongly
Reaction of chlorine with NaOH
2OH- + Cl2 -> Cl- + ClO- + H2O
2NaOH + Cl2 -> NaCl + NaClO + H2O
Green gas formed from colourless solution
Chlorine reaction with water
Cl2 + H2O <=> HCl + HClO
Sterilise drinking water and swimming pools
Equillibrium shifts right once microorganisms killed so little Cl2 left
In sunlight:
2Cl2 + 2H2O -> 4HCl + O2
Colours of halide solutions
Cl- pale green
Br- orange
I- brown
Why does oxidising ability reduce down the halogens
F more readily accepts electrons
Due to smaller atomic radius
And less shielding
Why does reducing ability increase down the halogens
Outer shell further away
Can lose electrons more readily
Increased shielding and less nuclear attraction
Reaction of NaF with sulfuric acid
NaF + H2SO4 -> NaHSO4 + HF
White misty fumes
Reaction of NaCl with sulfuric acid
NaCl + H2SO4 -> HCl + NaHSO4
White misty fumes
Reaction of NaBr with sulfuric acid
2NaBr + 3H2SO4 -> 2NaHSO4 + Br2 + SO2 +2H2O
White misty fumes and brown vapour
Reaction of NaI with sulfuric acid
2NaI + 3H2SO4 -> 2NaHSO4 + I2 + SO2 + 2H2O
6NaI + 7H2SO4 -> 6NaHSO4 + 3I2 + S + 4H2O
8NaI + 9H2SO4 -> 8NaHSO4 + 4I2 + H2S + 4H2O
White misty fumes purple vapour yellow solid rotten egg smell black solid formed
Test for halide ions
Add dilute HNO3
Add AgNO3
Cl: Ag+ + Cl- -> AgCl white precipitate, dissolves in dilute and concentrated ammonia
Br: Br- + Ag+ -> AgBr cream precipitate dissolves in concentrated ammonia
I: I- + Ag+ -> AgI yellow precipitate which does not dissolve in ammonia
H2SO4 not used to test as it is corrosive and produces toxic gases
How to test for carbonate ions
Addition of MgNO3
Positive result: white precipitate
Test for ammonium ions
Add NaOH
Warm gently
Test gas with damp red litmus paper
Positive result: paper changes blue
