3.1.3 halogens

What type of molecules do halogens exist as

diatomic molecules

What sub-shells are the outermost electrons of halogens present in

Two electrons in the s sub shell and 5 in the p sub shell

What ions do halogens form?

1- ions (halides)

Describe the trend in boiling point as you go down group 7

Boiling point increases

More electrons

Stronger London forces

More energy required to overcome intermolecular forces

What occurs when chlorine is added to a solution in water

Turns pale green

What occurs when bromine is added to a solution in water

Turns orange

What occurs when iodine is added to a solution in water

Turns brown

What occurs when chlorine is added to an organic solution ( in cyclohexane)

Top layer turns pale green

What occurs when bromine is added to an organic solution ( in cyclohexane)

Top layer turns orange

What occurs when iodine is added to an organic solution ( in cyclohexane)

Top layer turns violet

How can you diffirentiate between solutions of iodine and bromine that may appear a similar colour

Non polar organic solvent (eg cyclohexane ) added

Mixture shaken

In cyclohexane colours easier to distinguish

Iodine deep violet and Bromine orange

Describe the trend in reactivity as you go down group 7

Reactivity decreases

Atomic radius increases

Greater shielding - Weaker nuclear attraction

Form -1 ions less easily down the group

What ions will chlorine displace

Bromide and Iodide ions

What ions will bromine displace

Iodide ions

What ions will iodine displace

None

What occurs when chlorine is added to a solution of bromide ions + the equation

Chlorine will displace bromide ions

Orange colour from Br2 formation

Cl2 (aq) + 2BR-(aq) = 2CL-(aq) + Br2(aq)

What occurs when chlorine is added to a solution of iodide ions + the equation

Chlorine will displace iodide ions

Violet colour from I2 formation

CL2(aq) + 2I-(aq) = 2CL-(aq) + I2(aq)

What occurs when bromine is added to a solution of chlorine ions + the equation

No reaction as bromine is less reactive than chlorine

What occurs when bromine is added to a solution of Iodide ions + the equation

Bromine will displace iodide ions

Violet colour from I2 formation

Br2(aq) + 2I-(aq) = 2Br-(aq) + I2(aq)

What occurs when iodine is added to a solution of chlorine ions + the equation

No reaction as iodine is less reactive than chlorine

What occurs when Iodine is added to a solution of Bromide ions + the equation

No reaction as iodine is less reactive than bromine

What is a disproportionation reaction? + example

A redox reaction in which the same element is both oxidised and reduced

Reaction of chlorine with water

Reaction of chlorine with cold , dilute sodium hydroxide

Describe the use of chlorine in water treatment + the equation that illustrates this

Water purification

Products of reaction are HCl and hypochlorus acid (HClO) - HClO ionises to make chlorate (ClO-) ions, which kill bacteria.

This makes water safe to drink/swim in

Cl2 (aq) + H20 (l) = HCLO(aq) + HCL (aq)

Describe the reaction of chlorine with cold , dilute aqueous sodium hydroxide + the equation that illustrates this

large conc of chlorate (CLO- ) ions fromthe NaClO formed

Solution is used in household bleach

Cl2(aq) +2NaOH(aq) = NaClO(aq) +NaCl(aq) + H20(l)

Evaluate the uses of chlorine

Beneficial in ensuring water is safe to drink and that bacteria are killed

Extremely toxic gas

Respiratory irritant in small conc and in large conc can be fatal

Chlorine in water can react with organic hydrocarbons and chlorinated hydrocarbons are said to be cancerous

Not adding chlorine to water would compromise the quality of drinking water and diseases may break out

What are the benefits of using chlorine for water purification

Beneficial in ensuring water is safe to drink and that bacteria are killed

Not adding chlorine to water would compromise the quality of drinking water and diseases may break out

What are the limitations of using chlorine for water purification

Extremely toxic gas

Respiratory irritant in small conc and in large conc can be fatal

Chlorine in water can react with organic hydrocarbons and chlorinated hydrocarbons are said to be cancerous

Aqueous halide ions react with aqueous silver ions to form ...
+ equation

Precipitates of silver halides

Ag+ (aq) + X- (aq) = AgX (s)

Describe the steps of the halide test

Add aqueous silver nitrate (AgNO3) to an aqueous solution of a halide

Silver halide precipitates will form different colours

Add aqueous ammonia to test the solubility of the precipitate

What is the result when Cl- reacts with aqueous silver ions
+ the equation that illustrates it

White precipitate forms

Ag+(aq) + Cl-(aq) = AgCl(s)

What is the result when Br- reacts with aqueous silver ions
+ the equation that illustrates it

Cream precipitate forms

Ag+(aq) + Br-(aq) = AgBr(s)

What is the result when I- reacts with aqueous silver ions
+ the equation that illustrates it

Yellow precipitate forms

Ag+(aq) + I-(aq) = AgI(s)

Describe the solubility of the silver chloride in NH3(aq)

Soluble in dilute NH3(aq)

Describe the solubility of the silver bromide in NH3(aq)

soluble in concentrated NH3(aq)

Describe the solubility of the silver Iodide in NH3(aq)

Insoluble in concentrated NH3(aq)

What is the ionic equation for the reaction between chloride ions and aqueous silver ions

Ag+(aq) + Cl-(aq) = AgCl(s)

What is the ionic equation for the reaction between iodide ions and aqueous silver ions

Ag+(aq) + I-(aq) = AgI(s)

What is the ionic equation for the reaction between bromide ions and aqueous silver ions

Ag+(aq) + Br-(aq) = AgBr(s)