Group 7 Flashcards
what are group 7 elements known as
the halogens
how many outer electrons do group 7 elements have
7
why are group 7 elements in the p block
their outer electrons are in the p subshell
what do group 7 elements exist as
diatomic molecules
what is the trend in atomic radius down the group
increases
why does atomic radius increase down the group
- more shells-more shielding
- nuclear attraction on outer electrons decreases
- atomic radius increases
why is the ionic radius of a group 7 element bigger than the atomic radius
- atoms gain electrons to form x- ions
- same protons more electrons
- more electron-electron repulsion
trend in boiling point down group 7
increases
what is the trend in volatility down the group
they become less volatile
why does boiling point increase (and volatility decrease) down group 7
-Mr increases- more electrons
_VDW forces between molecules increases
-more energy needed to overcome forces of attraction
trend in electronegativity down group
decreases
why does electronegativity decrease down group
- more shells- more shielding
- nuc attraction on outer electron decreases as atomic radius increases
trend in first ionisation energy down group
decreases
why does first ionisation energy decrease
- more shells- more shielding
- nuc attraction on outer electron decreases as atomic radius increases
appearance of chlorine
pale green gas
state of chlorine at room temperature
gas
colour of aqueous solution of chlorine
very pale green
colour of chlorine in cyclohexane
very pale green
appearance of bromine
red/brown liquid
state of bromine at room temp
liquid
colour of bromine in aqueous solution
orange
colour of bromine in cyclohexane
orange
appearance of iodine
grey solid
state of iodine at room temp
solid
colour of iodine in aqueous solution
brown
colour of iodine in cyclohexane
purple
why are halogens more soluble in cyclohexane than water
they themselves are non polar like cyclohexane
trend in solubility of halogen in water down group
decreases
why does solubility in water decrease down group
halogen molecule becomes larger
what does a series of displacement reactions provide evidence for
the trend in oxidising powers of the halogens
method for displacement reactions
- add solution of each halogen to a solution of potassium halide in turn
- note any colour changes and decide whether a reaction has occurred
- add cyclohexane and note the clour in the organic (top layer)
what will the colour of the organic layer in displacement reactions tell you
which halogen is now present
colour of organic top layer:
KBr + Cl2
orange- Br2
colour of organic top layer:
KI + Cl2
pink/purple - I2
colour of organic top layer:
KCl + Br2
orange- Br2
colour of organic top layer:
Br2 + KI
purple/pink- I2
colour of organic top layer:
I2 + KCl
purple/pink- I2
colour of organic top layer:
KBr + I2
pink/purple- I2
oxidising agent
substance which accepts electrons
why are halogens oxidising agents
they all take electrons readily to form ions
X2 +2e- > 2X-
what happens to the halogens ability to act as oxidising agents as you go down the group
decreases
why does halogens ability to act as oxidising agents decrease down group
- become less reactive down group
- chlorine is smallest atom (out of chlorine, bromine, iodine)
- has strongest nuc attraction on outer electrons (fewer shells)
- best at gaining electrons
trend in reactivity Cl2 > Br2 > I2
chlorine most reactive- iodine least
if X is higher up in group than Y…
X is able to oxidise Y
what is a reducing agent
electron donor (is itself oxidised)
can halide ions act as reducing agents
yes but to different extents
what is the oxidation number of sulphur in sulphuric acid
+6
test for sulphuric acid
indicator paper turns red
oxidation number of sulphur in sulphur dioxide
+4
test for sulphur dioxide
acidified dichromate paper: orange > green
oxidation number of sulphur in its element
0
test for sulphur
yellow solid
oxidation number of sulphur in hydrogen sulphide
-2
test for hydrogen sulphide
lead acetate paper: white > black
what happens to the halide ion if sulphuric acid is reduced by it
it will be oxidised to the halogen molecule X2
2X- > X2 + 2e-
method to react halide on with sulphuric acid
- put 0.1g solid halide compound in test tub
- add 10 drops conc. sulphuric
- warm if necessary
- identify products
initial observations NaCl + sulphuric
white fumes (HCl made)
subsequent observations NaCl + sulphuric
no further change
initial observation: NaBr + sulphuric
white fumes (HBr)
subsequent observations: NaBr + sulphuric
brown fumes (Br2)
SO2 detected
initial observation: NaI + sulphuric
white fumes (HI)
subsequent observations: NaI + sulphuric
purple fumes (I2)
SO2,S, H2S all detected
what is the initial observation in all halide ion and sulphuric acid reactions
white fumes
what are the white fumes
the hydrogen halide as a gas
why is NaCl + H2SO4 not a redox reaction
- no change in oxidation states
- example of proton transfer ie acid/base reaction
why is there no further reaction between HCl produced and sulphuric acid
chloride ion cannot reduce sulphuric acid
why can halides act as reducing agents
they are able to lose electrons to form the respective halogen
what is the trend in reducing strength down the group of halides
increases
why does reducing strength of halides increase down group
-they become less good at holding onto their electrons (size increases, attraction on outer electrons decreases)
strongest oxidising agent group 7
flourine
strongest reducing agent group 7
iodide
test for halide ions
- make a solution of the substance to be tested
- add dilute nitric acid to remove other ions that interfere with test results by giving precipitates
- add silver nitrate solution
- observe colour of precipitate
Cl- PPT colour
white
name and formula of PPT that Cl- forms
silver chloride
AgCl
Br- PPT colour
cream
name and formula of PPT that Br- forms
silver bromide
AgBr
I- PPT colour
yellow
name and formula of PPT that I- forms
silver iodide
AgI
why do F- ions not form a ppt with silver nitrate
silver fluoride is soluble in water
Overall equation silver nitrate and sodium chloride
AgNO3 + NaCl > AgCl + NaNO3
Ionic equation silver nitrate + sodium chloride
Ag + Cl > AgCl
General ionic equation for test for halide ions
Ag + X > AgX
How to test for trends in solubility of the silver halide precipitates
Add dilute ammonia solution to each PPT and see if it dissolves
If not, add conc ammonia solution and see if it dissolves
What is silver chlorides solubility in ammonia
Soluble in dilute NH3
What is silver bromides solubility in ammonia
Insoluble in dilute NH3
Soluble in conc NH3
What is silver iodides solubility in ammonia
Insoluble in dilute and conc NH3
What is the trend in solubility in ammonia solution from silver chloride to silver iodide
Decreasing soluble
What does the use of ammonia solution help to distinguish between
Silver halide precipitates when the difference between their colours is not easy to identify
Disproportionation
A redox reaction in which the same element is both oxidised and reduced
Equation for the reaction of chlorine with water
Cl2 + H20 > HCl + HClO
<
(Reversible)
Where is an equilibrium established between in the reaction between chlorine and water
The chlorine, water, hydrochloric acid and chloric (I) acid
What is chlorine in the reaction between the reaction of chlorine and water
Both oxidised and reduced
How can chlorine be detected
Very pale green colour
How can hydrochloric acid be detected
Turns universal indicator paper red
How can chloric (I) acid be detected
Universal indicator paper red then bleached white
What happens to the chloric acid that is formed from the reaction between chlorine and water
Decomposes to hydrochloric acid and oxygen
Equation for decomposition of chloric (I) acid
2HClO > 2HCl + O2
What is the reaction between chlorine and water accelerated by
Sunlight and certain catalysts
Why is the reaction between chlorine and water accelerated by sunlight
Breaks bonds so lowers activation energy
What is produced when chlorine reacts with water in the presence of sunlight
Hydrochloric acid and oxygen
What is the benefit of using chlorine in water treatment
It kills bacteria
What is the risk in using chlorine in water treatment
It’s toxic
Chlorinated hydrocarbons are carcinogenic
What does the reaction of chlorine with cold dilute sodium hydroxide solution produce
Sodium chloride, sodium chlorate (I) and water
Equation for reaction between chlorine and sodium hydroxide solution
Cl2 + NaOH > NaCl + NaClO + H2O
What happens to the colour and smell of the chlorine during the reaction between it and NaOH solution
The green colour fades and the smell is less pungent
Why is the reaction between chlorine and sodium chloride a disproportionation reaction
Chlorine is both oxidised and reduced
Main use of sodium chlorate
Domestic bleach
