1.8 Halogens

fluorine appearance

Yellow gas

Chlorine appearance r.t.p

Yellow-green gas

Bromine appearance at r.t.p

Red-brown liquid

-heated Vapour

Iodine appearance at r.t.p

grey-black solid

Purple vapour when heated

Solidity of halogens

Dissolve in water (except F2)

Dissolve readily in non aqueous solvents

Chlorine in water

Pale green/colourless solution

Chlorine in hexane

Colourless solution

Bromine appearance in water

Yellow or orange or brown solution

Bromine appearance in hexane

Red solution.

Iodine in water

Yellow-brown solution

Iodine in hexane

Purple solution

Atomic radius down group

Increases cus atomic number increases so do number of electrons and electron shells present. As more shells filled, atom increases in size

Decreasing electronegativity

Bigger atom, more nucleus shielded by extra inner electrons.extra shielding means effect of nuclear charge reduced so ability of nucleus to attract electrons is reduced

Increasing boiling points

halogen non-polar, so attraction between molecules due to weak van der waals forces, size of molecule increses down, strenght of van der waals forces between moleucles also increase.

decreasing first ionisation energy

outer electrons increasinly further from nucleus, and outer electrons shielded from nuclear charge by filled shells of electrons, ability of nucleus to hold electrons is reduced

decreasing bond energies

atomic radii of elements increase, so increased bond lengths between atoms in a molecule decreased bond energies. F-F bond unexpectedly weak becus small size of fluorine atom brings lone pairs of electrons in F2 closer together than other molecules,

solubility down group

decreases as chlroine bromine slightly solulbe in water, iodine insoluble, as they non-polar with weak van der waals forces  between them and water is polar with strong hydrogen bonds between molecules, halogens soluble in hexane as its non polar.

oxidation states down group 

fluroine oxidation state of -1 but rest have empty d orbitals so can promote electrons to give oxidaition state +1 - +7 , oxidising agents 

chorine reaction with water

Cl2 (g) + H20 → HCl (aq) + HOCl (aq)

hydrochloric acid and hypochlorous ( hydrogen chlorate (I) ) which is chlorine water

what type of reaction is chlroine water

disproportionation reaction as chlroine has been oxidised in HOCl and reduced in HCl

test for chlorine

damp litmus paper turns red then bleaches white, as its acidic then hypochlroite ions bleach it

chlroine with cold dilute sodium hydroxide solution

Chlorine + sodium hydroxide → sodium chloride + sodium chlorate (I) + water

Cl2 (g) + 2NaOH(aq) → NaCl(aq) + NaClO(aq) + H2O (l)

Ionic equation for chlroine with cold dilute NaOH

2OH- + Cl2 → Cl- + ClO- + H2O

chlorine with hot contentrated sodium hydroxide solution 

Chlorine + sodium hydroxide → sodium chloride + sodium chlorate (V) + water

3Cl2(g) + 6NaOH (aq) → 5NaCl (aq) + NaClO3 (aq) + 3H2O (l)

why this diff from cold dilute 

as chlorate (I) ion disproportionates into chlroide and chlorate (V) ions

Chlorate (I) iond → chloride ions + chlorate (V) ions

3ClO- (aq) → 2Cl- (aq) + ClO3- (aq)

ionic equation for chloride + hot concentrated sodium hydroxide 

6OH- + 3Cl2 → 5Cl- + ClO3- + 3H2O

chlorine + sodium hydroixde observation 

yellow-green gas dissolves to from colourless solution 

halogens oxidising agent and reason

fluorine best, iodine worst,

as electorns gained by fluroine will have stronger attraction to nucleus, it is not subjected to as much shielding and closer to nucleus,

halogens reduicng agents

iodine best reducing agent, fluorine worst

as electron lost from iodine shell far from nuceleus so attraction to nucleus is relatively weak, and outer electron subjected to large amount of shielding as many filled inner shells

displacement reaction of chlorine with potassium bromide (chlorine more reactive)

chlorine + potassium bromide → potassium chloride + bromine

Cl2 (aq) + 2KBr(aq) → 2KCl(aq) + Br2(aq) yellow orange

ionic equation of chorine + potassium bromide

Cl2(aq) + 2Br-(aq) → 2Cl- (aq) + Br2(aq)

half equation of chlorine + potassium bromide

Cl2 + 2e- → 2Cl- (reduction)

2Br- → Br2 + 2e-

Fluoride reaction with concentrated sulfuric acid

NaF + H2SO4 -> NaHSO4 + HF

Why fluoride get no reactions

Fluoride ion poor reducing agent , don’t give up electrons easily

Fluoride names of products

sodium hydrogensulfate, hydrogen fluoride

Fluoride observations

misty fumes, pungent smell, gas produced (HF), solid disappears, heat released

Chloride reaction with concentrated sulfuric acid

NaCI + H2SO4 -> NaHSO4 + HCI

Chloride additional reactions

None as Poor reducing agent

Chloride products

sodium hydrogensulfate, hydrogen chloride

Chloride observations

misty fumes, pungent smell, gas produced (HCI), solid disappears, heat released

Bromide reaction with concentrated sulfuric acid

NaBr + H2SO4 -> NaHSO4 + HBr

Bromide additional reaction

Sulfur atom reduced +6 to +4

2HBr + H2S04 -> Br2 + SO2 + 2H2O

Bromide name of products

sodium hydrogensulfate, hydrogen bromide, bromine, sulfur dioxide, water,

Bromide observations

misty fumes (HBr), gas produced (HBr/ SO2), solid disappears, red-brown vapour (Br), heat released, pungent smell (HBr/SO2/Br2)

Iodide reaction with concentrated sulfuric acid

NaI + H2SO4 -> NaHSO4+ HI

Iodide ion additional reactions, Sulfur atom reduced from +6 to +4/0/-2

2HI + H2SO4 → I2 + SO2 + 2H20

6HI + H2SO4 → S + 3I2 + 4H20

8HI + H2SO4→ H2S + 4I2 + 4H20

Name of products iodide

sodium hydrogensulate, hydrogen iodide, iodine, sulfur doxide, sulfur, hydrogen sulfide, water

Iodide observation

misty fumes (HI), gas produced (HF/SO4), solid disappears, grey-black solid and purple vapour (I2), heat released, pungent smell (HI/SO/ l2), rotten egg smell (H2S), yellow solid (S)

why no additional reactions with Sodium halides with concentrated phosphoric acid equation

harder to reduce phosphoric acid

Sodium halides with concentrated phosphoric acid equation

NaF + H3PO4 → NaH2PO4 + HF

NaCl + H3PO4 → NaH2PO4 + HCl

NaBr + H3PO4 → NaH2PO4 + HBr

NaI + H3PO4 → NaH2PO4 + HI

name of products of Sodium halides with concentrated phosphoric acid

sodium dihydrogen phosphate, hdyrogen fluroide/chlroide/bromide/iodide

observations of Sodium halides with concentrated phosphoric acid equation

gas releases, misty fumes (HF/HCl/HBr/HI), solid disappears, heat released

chlroine reacts with water equation

Cl2 + H2O → HOCl + HCl

Chlorine to drinking water Advantages

• Cheaper than ozone

• Provides residual protection as still present in water when it reaches the consumer

• More soluble in water than ozone

Chlorine to drinking water Disadvantages

• Cannot kill some microorganisms

• Leave chemicals in water

• Unpleasant taste

• Toxic to humans so low quantities used

Ozone to drinking water Advantages

• Kills more different types of microorganisms than chlorine

• Breakdown product is oxygen

• No residual chemicals in water

• Removes metal and organic particles from weather

• No unpleasant taste

Ozone to drinking water Disadvantage

• More expensive than chlorine

• Does not provide residual protection against microorganisms

• Less soluble in water than chlorine so requires special mixing techniques