Group 7

what colour and state is fluorine at room temperature

pale yellow gas

what colour and state is chlorine at room temperature

green gas

what colour and state is bromine at room temperature

orange/ brown liquid

what colour and state is iodine at room temperature

grey/black solid

what colour vapour does iodine very easily form

purple

what happens to the melting and boiling points going down group 7

they increase → volatility decreases down group

what type of molecules are halogens

diatomic

why does mpt decrease down the group

• atomic radius increases

• more electron shells

• outermost electrons are further away from positive nucleus so is less strongly attracted to it

what is the trend in bond enthalpies down group 7 between atoms of group 7 diatomic molecules, and what is the exception to this
e.g. energy needed to break covalent bond between Br-Br vs energy needed to break I-I

• higher bond enthalpy = stronger covalent bonds

• bond enthalpies decrease down group 7 = bonds strengths decrease going down the group

• exception = fluorine = smaller bond enthalpy than chlorine and bromine

• lone pairs on fluorine get so close to each other in a fluorine molecule that they cause repulsion which decreases the bond strength

what is the trend in electronegativites down group 7

• electronegativity decreases down group

• larger atoms / atomic radius increases / more shells → outermost electron is further away from nucleus

• weaker attraction between nucleus and shared pair of electrons

what type of structures are halogens with what forces between the diatomic molecules

• simple molecular structure

• weak VDWs

when a halogen reacts with a metal, what sort of agent is it?

• oxidising agent

• accepts an electron from metal atom to become an ion with a 1- charge

what happens to the oxidising power of the halogens as you go down the group

decreases→ halogens get less reactive

halogens ability to accept an electron decreases

define electronegativity

how strongly an atom attracts the electrons in a covalent bond towards itself

order halogens in order of reactivity

fluroine, chlorine, bromine, iodine

what happens to the reducing power of halide ions as you move down the group

• increases going down the group → ions are more likely to donate electrons going down group

why does reducing power of halide ions increase going down the group

• halide ions become larger

• outermost electron gets further away from nucleus

• outermost electron experience more shielding due to more shells

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

• electron lost more easily → reducing power increases

what 2 substances can you use to test for halides

• silver nitrate

• ammonia

give the full equation and half equation for the reaction of chloride ion and silver nitrate

AgNO₃ (aq) + NaCl (aq) → AgCl (s) + NaNO_{3 (aq)}

Ag⁺ (aq) + Cl^- → AgCl (s)

when testing for halide ions suing silver nitrate, list the colour of the precipitates formed

1. with chloride

2. with bromide

3. with iodide

1. white

2. cream

3. yellow

why do you add ammonia to the precipitates after doing a halide test with silver nitrate

• as white white, cream and yellow precipitates can look very similar

describe the test of adding ammonia to the AgX precipitates and the results

• dilute followed by concentrated ammonia is added to silver halide solution

• precipitate redissolves in dilute ammonia to form colourless solution→ halide = chloride

• precipitate doesn’t redissolve in dilute ammonia but does in concentrated → halide = bromide

• precipitate doesn’t redissolve in either dilute or concentrated ammonia → halide = iodide

reaction of halide ions with silver nitrate and ammonia solutions
learn this table:

okay

when testing for halides using silver nitrate, why do you have to add nitric acid (aq) first to the solution being tested

• removes any other ions that could give a precipitate with silver nitrate

• e.g. carbonate ions

• CO₃^2- + 2H⁺ → CO₂ + H₂O

give the chemical equation for when AgCl reacts with dilute ammonia

AgCl + 2NH₃ → (Ag(NH₃)₂)⁺ → Cl^-

give the chemical equation for when AgBr reacts with concentrated ammonia

AgBr + 2NH₃ → (Ag(NH₃)₂)⁺ → Br^-

what is a disproportionation reaction

a reaction in which the same species is both oxidised and reduced

give 2 examples of a disproportionation reaction

1. chlorine with dilute alkali
   - chlorine gets oxidised and reduced at same time

2. chlorine with water

give the equation for the disproportionation reaction of chlorine in cold alkali

1. chemical

2. ionic

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

2. Cl₂ (aq) + 2OH^- (aq) → Cl^- (aq) + ClO^- (aq) + H₂O (aq)

• increase in ox. no. from 0 to +1 in ClO^- (aq) = oxidation

• decrease in ox. no from 0 to -1 in Cl^- (aq) = reduction

learn this table for the reaction of halides with concentrated sulphuric acid

okay

what can chlorine be used for

clean water and make it drinkable

give the equation for the disproportionation reaction of chlorine and water

Cl_2(aq) + H₂O_(l) → HCl_(aq) + HClO_(aq)