Chapter 10 - Group 7 Halogens

what does fluorine look like at room temperature?

yellow gas

what does chlorine look like at room temperature

pale green gas

features of fluorine and chlorine

• very reactive

• toxic

what does bromine look like at room temperature?

orange-brown liquid

features of bromine

• Very reactive

• Toxic

• Often used as bromine water

• Volatile

what does iodine look like at room temperature

grey crystals (solid)

what does iodine look like as a gas

purple gas

what does iodine look like as a liquid

brown liquid

features of iodine

• Sublimates to purple gas

• Used in antiseptics

• Reactive

• toxic

electronegativity defintiion

the power of an atom to attract the shared pair of electrons in a covalent bond

TREND - electronegativity

• decreases as you go down the group

• Atomic radius increases and shielding increases

• So electrostatic force of attraction between nucleus and outermost electron decreases

• So electronegativity decreases

TREND - melting points

• Melting points increase as you go down the group

• Strength of VDW forces increases as you go down the group due to larger atomic number

• So more energy is needed to overcome these forces as you go down the group

• so less volatile as you go down the group

oxidising ability definition

Refers to an atoms ability to gain electrons

what are halogens oxidised to

• Occurs for halogen molecules

• Halogen molecules oxidised to 2 halide ions

TREND - oxidising ability

• Oxidising ability decreases as you go down the group

• More shielding as you go down the group

• So weaker electrostatic force of attraction between nucleus and outermost electron

• So harder to gain an electron, so less reactive and has low oxidising ability

reducing ability definition

Refers to an atoms ability to lose electrons

what are halogens reduced to

• Occurs for halide ions

• Halide ions lose electrons to become halide molecules

TREND - reducing ability

• Reducing ability increases as you go down the group

• The larger the ionic radius, the weaker the efoa so easier to lose an electron

oxidising agent definition

electron acceptor

reducing agent definition

electron donor

halides are only displaced by….

more reactive halogens

reacting sodium chloride with concentrated sulphuric acid

NaCl (s) + H₂SO₄ (l)  → NaHSO₄ (s) + HCl (g)

what type of reaction is this:

acid-base reaction

observations for this reaction

Misty white fumes - Hydrogen chloride gas aka salt gas

why isn’t this a redox reaction:

as chlorine isn’t a strong enough reducing agent so oxidation states don’t change

sodium bromide reacting with concentrated sulphuric acid

this is an acid-base reaction

2HBr (g) + H₂SO₄ (l) → SO₂ (g) + 2H₂O (l) + Br₂ (l)

this is a redox reaction

reaction to form bromine with sulphuric acid and sodium bromide is

H2SO4 + NaBr → Na2SO4 + SO2 +Br2+ 2H2O

half equation for redox reaction of bromine

2Br + SO42 + 4H+ → Br2 + SO2 +2H2O

observation for this reaction

• Steamy fumes - Hydrogen bromide gas

• Brown fumes - Bromine gas

• Sulphur dioxide gas is colourless

• exothermic reaction

sodium iodide reacting with concentrated sulphuric acid

NaI (g) + H₂SO₄ → NaHSO₄ (s) + HI (g) 

this is an acid base reaction

8HI (g) + H₂SO₄ (l) → H₂S (g) + 4H₂O (l) + I₂ (s)

H2SO4 + 2HI + SO2 → I2 + 2H2O

H2SO4 + 6HI → S + 4H2O + 3I2

half equation for reaction with iodine creating solid sulphur

SO42- + 8H+ + I-→ S + 4H2O + 3I2

half equation for iodine and producing sulphur dioxide

H2SO4 + 2HI → SO2 + I2 + 2H2O

observations for this reaction

• Steamy fumes - Hydrogen iodide

• Black solid - Iodine

• Bad egg smell - Hydrogen sulphide gas

• Yellow solid - sulphur

identifying halides using silver ions test

Silver nitrate and nitric acid formed a silver halide precipitate

1. If chloride ions white precipitate

2. If bromide ions cream precipitate

3. If iodide ions yellow precipitate

further test for halide ions using ammonia

• Silver chloride is able to dissolve in dilute ammonia

• Silver bromide only dissolves in concentrated ammonia

• Silver iodide doesn’t dissolve in concentrated or dilute ammonia

simplest ionic equation for halide ion test if precipitate formed is:

Ag+ + I- → AgI

direct chlorination equation - this occurs with no sunlight

Cl₂ (g) + H₂O (l) → HClO (aq) + HCl (aq)

what type of reaction is this?

disproportionation - chlorine is simultaneously oxidised and reduced

chlorine with water reaction (sunlight present)

2Cl₂ (g) + 2H₂O (l) → 4HCl (aq) + O₂ (g)

• Chlorine is rapidly lost from pool water when sunlight is present so must constantly be refilled

uses of chloric acid

oxidising agent, kills bacteria by oxidation and is also a bleach

what can you use for ALTERNATE CHLORINATION

 sodium chlorate or calcium chlorate which dissolved in water to form chloric acid

SODIUM CHLORATE REACTION WITH WATER

NaClO + H₂O → Na⁺ + OH^- + HClO

chlorine reaction with dilute cold sodium hydroxide

Cl_2, + 2NaOH → NaClO + NaCl + H₂O

• This is an oxidising agent

• This is an active ingredient in bleach

• This is also a disproportionation reaction