Group VII

Group VII

Chlorine

Explode with H2 under light

Cl2 + H2 -> 2HCl

Bromine

Slow reaction, heat at 200ºC with catalyst

Br2 + H2 -> 2HBr

Iodine

No reaction unless heated strongly

I2 + H2 2HI

Increasing ionisation energy Increasing electronegativity Increasing oxidation power Increasing reduction power

Fluorine

Explode with H2 under all F2 + H2 -> 2HF conditions

Fluorine Chlorine Bromine Iodine

Stronger Van Der Waals forces Increasing atomic/ionic radii Increasing colour intensity

Reaction with hydrogen

Reaction with water Fluorine

Violent reaction oxidise water to oxygen

F2 + H2O -> 2HF + 1/2O2

Chlorine

Reversible reaction

Cl2 + H2O HCl + HClO

Bromine

Equililibrium to the left

Br2 + H2O HBr + HBrO

Iodine

Almost insoluble

I2 + H2O HI + HIO

Reason: H-X bond formed release less energy

Reaction with H2SO4

Fluoride

Chloride

Bromide

Iodide

Steamy fumes of HF

NaF + H2SO4 -> HF + NaHSO4

Steamy fumes of HCl

NaCl + H2SO4 -> HCl + NaHSO4

Brown fume of Br2 and HBr

NaBr + H2SO4 -> HBr + NaHSO4 2HBr + H2SO4 -> Br2 + SO2 + 2H2O

NaI + H2SO4 -> HI + NaHSO4 Purple fumes of 2HI + H2SO4 -> I2 I2 + SO2 + 2H2O

Reaction with NH3

Decomposition of HX

Fluoride

No ppt

-

Chloride

White ppt of AgCl

Soluble in dil. NH3

Bromide

Cream ppt of AgBr

Soluble in conc. NH3

Iodide

Yellow ppt of AgI

Insoluble in NH3

AgCl (s) Ag+ (aq) + Cl- (aq) Ag+(aq) + 2NH3(aq) [Ag(NH3)2]+ (aq)

Reaction of Cl2 with NaOH Cold: 2NaOH + Cl2 -> NaCl + NaClO + H2O Hot: 3NaClO -> 2NaCl + NaClO3

Hydrogen Fluoride

Stable to heat

-

Hydrogen Chloride

Stable to heat

-

Hydrogen Bromide

Decompose slightly, brown fumes observed

2HBr-> H2 + Br2

Easily decomposed, Hydrogen Iodide dense purple fumes observed

2HI -> H2 + I2

Reason: atomic radius of X increases, causing bonding parit of electron to be futher awayfrom nuclei of H and X. Energy of H-X bond decrease as the electrons are less strongly attracted. Thermal stability of H-X decreases down the group.