8.2 Group 7 Flashcards
what are the physical properties of group 7 elements?
most reactive non-metal group
do not occur in their natural state
what is the trend in boiling point in group 7?
the boiling point increases as you go down the group
why does the boiling point increase as you go down group 7?
increased number of electrons
stronger London forces
more energy is needed to overcome the stronger forces
appearance and state of F2
pale yellow
GAS
appearance and state of Cl2
pale green
GAS
appearance and state of Br2
red-brown
LIQUID
appearance and state of I2
shiny grey
SOLID
what is the electronic configuration of group 7 elements?
7 electrons in outer shell
2 electrons in s sub-shell
5 electrons in p sub-shell
why are group 7 elements oxidising agents?
they gain an electron to form -1 ions
Cl2 + e- ——–> 2Cl-
they accept electrons given from another species which means it has had to oxidise another species
what is the trend in reactivity of group 7 elements?
reactivity decreases because as you go down the group:
- atomic radius increases
- shielding increases
- less nuclear attraction between nucleus and electrons
- less ability to attract an electron to ionise
what is a disproportionation reaction?
when oxidation and reduction happens in the same reaction to the same species
what is an example of a disproportionation reaction?
chlorine and water
chlorine and sodium hydroxide
chlorine + water
chloric (I) acid
hydrochloric acid
chlorine + water equation
Cl2 (aq) + H2O (l) ——-> HClO (aq) + HCl )aq)
Cl in Cl2
= 0
Cl in HClO
= +1 (oxidation)
Cl in HCl
= -1 (reduction)
chlorine has been oxidised and reduced so this is a disproportionation reaction
what is HClO?
chloric (I) acid
it is what kills bacteria in bleach
acts as a weak bleach
chlorine + NaOH
sodium chlorate (I)
NaCl
water
chlorine + cold dilute sodium hydroxide
Cl2 (aq) + 2NaOH (aq) –> NaClO (aq) + NaCl (aq) + H2O (l)
Cl in Cl2
= 0
Cl in NaClO
= +1 (oxidation)
Cl in NaCl
= -1 (reduction)
chlorine has been oxidised and reduced so this is a disproportionation reaction
what is NaClO?
sodium chlorate (I)
used in household bleach
why is chlorine dangerous?
- large conc can be dangerous
- can react with hydrocarbons to form chlorinated hydrocarbons which can cause cancer
why is chlorine useful?
- ensures water is drinkable and safe
- kills bacteria
- kills diseases such as typhoid and cholera
- used to make bleach
Cl2 in water
pale green
Br2 in water
orange
I2 in water
brown
I2 in cyclohexane
purple
why is cyclohexane used in displacement reactions?
to make the colour changes more clearer
what happens during a displacement reaction?
the halogen displaces the halide
the halide becomes a diatomic halogen and solution changes colour
how are halide ions tested?
add aqueous silver ions to form silver halide precipitates with specific colours
