Group 7 Flashcards
(24 cards)
Trends in melting & boiling temps?
increases down the group as London forces increases: due to size (of electron cloud) & no. electrons
Equations for change of state?
- when Br left at room temp - gives off brown vapour - as bp (59 Celsius) not much higher than room temp:
Br2 (l) –> Br2 (g) - when I warmed - most of it changes directly into vapour w/o melting aka sublimation:
I2 (s) –> I2 (g)
Trend in electronegativity?
decreases as go down group as - atoms get larger & dis between +ve nucleus & bonding electrons increases & more shielding * atom’s ability to attract pair of electrons in a covalent bond - increases w…
- bigger nuclear charge
- shorter dis between nucleus & bonding pair of electrons
- (fewer energy levels) decreased shielding effect of electrons in inner energy levels
Trend in reactivity?
decreases down group
(due to their high electronegativity - most reactions involve acting as oxidising agents & gaining electrons to form -ve ions/becoming delta -ve part of a polar molecule
- reactivity increases w…
- bigger nuclear charge
- shorter dis between nucleus & bonding pair of electrons
- (fewer energy levels) decreased shielding effect of electrons in inner energy levels
Reactions w metals in Group 1 & 2?
- reactions most vigorous between elements at bottom of Groups 1 & 2 and top of G7
- products of reactions r salts - ionic solids that r usually white
- all reactions involve electron transfer to halogen so - redox - halogen acts as oxidising agent
- ox num of halogen decreases from 0 to -1
- ox num of metal increases from 0 to +1 or +2
Halogen/halide displacement reactions?
*A more reactive halogen can displace a less reactive halogen from one of its compounds so:
- Cl displaces Br & I
- Br displaces I but not Cl
- I doesn’t displace Cl or Br
(aq solutions)
e.g. Cl2 + 2NaBr –> 2NaCl + Br2
- redox reactions
problem w interpreting colour changes in displacement reactions?
- similarity of some colours & variation in colour w concentration
e.g. Br(l): red-brown but Br (aq): orange or yellow depending on conc.
e.g. I(aq): may also appear brown at some concs
Cyclohexane in displacement reactions?
gd to add organic solvent like cyclohexane after reaction & shake tube
- halogens r more soluble in cyclohexane than in water so - halogen dissolves in organic upper layer - colour more easily seen here
- Cl: pale green
- Br: orange
- I: purple/violet
Cl more reactive than Br & I?
- smallest atom so - incoming electron gets closer to & is more attracted by protons in nucleus
- has smallest no. complete inner energy levels of electrons so - incoming electron experiences the least repulsion
Disproportionation reaction>
where one element undergoes both oxidation & reduction at the same time
Cl with water?
- dissolves to form solution aka chlorine water
- some of dissolved Cl reacts to form mix of 2 acids - HCl + HClO (chloric(I) acid)
- both acids colourless solutions so - no visible change
- disproportionation:
Cl2 + H2O —> HCl + HClO
0 to -1: Cl reduced
0 to +1 Cl oxidised - purpose: to disinfect water for drinking purposes & in pools - reduces risk of transmitting infections
Cl w cold alkali?
- when Cl added to: cold, dilute aq NaOH - reacts to form the salts of HCl & HClO aka: NaCl & NaClO (sodium chlorate(I) )
- disproportionation:
Cl2 + 2NaOH –> NaCl + NaClO + H2O
0 to -1 Cl reduced
0 to +1 Cl oxidised - NaClO - disinfectant & bleaching action
Cl w hot alkali?
- when Cl added to: hot, conc. NaOH sol - reacts to form: NaCl & NaClO3 (sodium chlorate(V) )
- disproportionation:
3Cl2 + 6NaOH –> 5NaCl + NaClO3 + 3H2O
0 to -1 Cl reduced
0 to +5 Cl oxidised - NaClO3 used in bleaching & as a weed killer
- Br & I react in similar ways
HClO (chloric(I) acid ionises to make…
HClO + H2O -> ClO- + H3O+
(chlorate(I) ions + acidic H3O+)
(reversible)
conc. sulfuric acid partial ionisation?
- contains very few ions when conc.
H2SO4 –> H+ + HSO4 -
(reversible) then…
HSO4 - –> H+ + SO4 2- - acts as ox agent so is reduced but - extent of reduction & products formed depend on species being oxidised
3 poss products: - SO2 (+6 to +4)
- S (+6 to 0)
- H2S (+6 to -2)
- decrease in ox num of S is the same as no. H+ ions & electrons in half-eqs
(half eqs on paper)
Observations & products for NaCl?
misty fumes, hydrogen chloride (HCl)
(no redox)
Observations & products for NaBr?
- misty fumes, hydrogen bromide (HBr)
- brown fumes, bromine (Br2)
- colourless gas w choking smell, sulfur dioxide (SO2)
Observations & products for NaI?
- misty fumes, hydrogen iodide (HI)
- purple fumes or black solid, iodine (I2)
- colourless gas w choking smell, sulfur dioxide (SO2)
- yellow solid, sulfur (S)
- colourless gas w rotten egg smell, hydrogen sulfide (H2S)
Halide ions reducing agents?
- lose electrons in reactions so - reducing agents
- down group ionic radius increases
- dis between nucleus & outer electrons becomes larger & more shielding so - attractive force gets weaker
- outer electron lost more readily
Testing for halide ions in solution?
- add dilute HNO3 to ensure any other anions (especially carbonate ions) r removed - as would also form precipitates
- ad silver nitrate sol
- add ammonia solution - dilute or conc. (if precipitate obtained)
- test can’t be used for F- ions in aq sol as - AgF soluble
- Ag+ (aq) + X- (aq) –> AgX(s)
- AgNO3 + NaCl –> AgCl + NaNO3
- AgCl + 2NH3 –> [Ag(NH3)2]+ + Cl-
Results for Cl- ions?
- add silver nitrate sol - white precipitate
- add dilute aq ammonia - soluble
- add conc. aq ammonia - soluble
Results for Br- ions?
- add silver nitrate sol - cream precipitate
- add dilute aq ammonia - insoluble
- add conc. aq ammonia - soluble
Results for I- ions?
- add silver nitrate sol - yellow precipitate
- add dilute aq ammonia - insoluble
- add conc. aq ammonia - insoluble
Hydrogen halides acting as gases?
- all colourless gases & exist as polar diatomic molecules
- readily react w water to form colourless acidic solutions
e.g. HF + H2O –> H3O+ + F- (same for all BUT - F only reversible one rest aren’t as - HF weak acid)
*hydriodic - react w NH3(g) to form salts - white ionic solids
