Group 7 Flashcards
1
Q
what are group 7 elements known as
A
the halogens
2
Q
how many outer electrons do group 7 elements have
A
7
3
Q
why are group 7 elements in the p block
A
their outer electrons are in the p subshell
4
Q
what do group 7 elements exist as
A
diatomic molecules
5
Q
what is the trend in atomic radius down the group
A
increases
6
Q
why does atomic radius increase down the group
A
- more shells-more shielding
- nuclear attraction on outer electrons decreases
- atomic radius increases
7
Q
why is the ionic radius of a group 7 element bigger than the atomic radius
A
- atoms gain electrons to form x- ions
- same protons more electrons
- more electron-electron repulsion
8
Q
trend in boiling point down group 7
A
increases
9
Q
what is the trend in volatility down the group
A
they become less volatile
10
Q
why does boiling point increase (and volatility decrease) down group 7
A
-Mr increases- more electrons
_VDW forces between molecules increases
-more energy needed to overcome forces of attraction
11
Q
trend in electronegativity down group
A
decreases
12
Q
why does electronegativity decrease down group
A
- more shells- more shielding
- nuc attraction on outer electron decreases as atomic radius increases
13
Q
trend in first ionisation energy down group
A
decreases
14
Q
why does first ionisation energy decrease
A
- more shells- more shielding
- nuc attraction on outer electron decreases as atomic radius increases
15
Q
appearance of chlorine
A
pale green gas
16
Q
state of chlorine at room temperature
A
gas
17
Q
colour of aqueous solution of chlorine
A
very pale green
18
Q
colour of chlorine in cyclohexane
A
very pale green
19
Q
appearance of bromine
A
red/brown liquid
20
Q
state of bromine at room temp
A
liquid
21
Q
colour of bromine in aqueous solution
A
orange
22
Q
colour of bromine in cyclohexane
A
orange
23
Q
appearance of iodine
A
grey solid
24
Q
state of iodine at room temp
A
solid
25
colour of iodine in aqueous solution
brown
26
colour of iodine in cyclohexane
purple
27
why are halogens more soluble in cyclohexane than water
they themselves are non polar like cyclohexane
28
trend in solubility of halogen in water down group
decreases
29
why does solubility in water decrease down group
halogen molecule becomes larger
30
what does a series of displacement reactions provide evidence for
the trend in oxidising powers of the halogens
31
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)
32
what will the colour of the organic layer in displacement reactions tell you
which halogen is now present
33
colour of organic top layer:
| KBr + Cl2
orange- Br2
34
colour of organic top layer:
| KI + Cl2
pink/purple - I2
35
colour of organic top layer:
| KCl + Br2
orange- Br2
36
colour of organic top layer:
| Br2 + KI
purple/pink- I2
37
colour of organic top layer:
| I2 + KCl
purple/pink- I2
38
colour of organic top layer:
| KBr + I2
pink/purple- I2
39
oxidising agent
substance which accepts electrons
40
why are halogens oxidising agents
they all take electrons readily to form ions
X2 +2e- > 2X-
41
what happens to the halogens ability to act as oxidising agents as you go down the group
decreases
42
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
43
trend in reactivity Cl2 > Br2 > I2
chlorine most reactive- iodine least
44
if X is higher up in group than Y...
X is able to oxidise Y
45
what is a reducing agent
electron donor (is itself oxidised)
46
can halide ions act as reducing agents
yes but to different extents
47
what is the oxidation number of sulphur in sulphuric acid
+6
48
test for sulphuric acid
indicator paper turns red
49
oxidation number of sulphur in sulphur dioxide
+4
50
test for sulphur dioxide
acidified dichromate paper: orange > green
51
oxidation number of sulphur in its element
0
52
test for sulphur
yellow solid
53
oxidation number of sulphur in hydrogen sulphide
-2
54
test for hydrogen sulphide
lead acetate paper: white > black
55
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-
56
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
57
initial observations NaCl + sulphuric
white fumes (HCl made)
58
subsequent observations NaCl + sulphuric
no further change
59
initial observation: NaBr + sulphuric
white fumes (HBr)
60
subsequent observations: NaBr + sulphuric
brown fumes (Br2)
SO2 detected
61
initial observation: NaI + sulphuric
white fumes (HI)
62
subsequent observations: NaI + sulphuric
purple fumes (I2)
SO2,S, H2S all detected
63
what is the initial observation in all halide ion and sulphuric acid reactions
white fumes
64
what are the white fumes
the hydrogen halide as a gas
65
why is NaCl + H2SO4 not a redox reaction
- no change in oxidation states
| - example of proton transfer ie acid/base reaction
66
why is there no further reaction between HCl produced and sulphuric acid
chloride ion cannot reduce sulphuric acid
67
why can halides act as reducing agents
they are able to lose electrons to form the respective halogen
68
what is the trend in reducing strength down the group of halides
increases
69
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)
70
strongest oxidising agent group 7
flourine
71
strongest reducing agent group 7
iodide
72
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
73
Cl- PPT colour
white
74
name and formula of PPT that Cl- forms
silver chloride
AgCl
75
Br- PPT colour
cream
76
name and formula of PPT that Br- forms
silver bromide
AgBr
77
I- PPT colour
yellow
78
name and formula of PPT that I- forms
silver iodide
AgI
79
why do F- ions not form a ppt with silver nitrate
silver fluoride is soluble in water
80
Overall equation silver nitrate and sodium chloride
AgNO3 + NaCl > AgCl + NaNO3
81
Ionic equation silver nitrate + sodium chloride
Ag + Cl > AgCl
82
General ionic equation for test for halide ions
Ag + X > AgX
83
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
84
What is silver chlorides solubility in ammonia
Soluble in dilute NH3
85
What is silver bromides solubility in ammonia
Insoluble in dilute NH3
Soluble in conc NH3
86
What is silver iodides solubility in ammonia
Insoluble in dilute and conc NH3
87
What is the trend in solubility in ammonia solution from silver chloride to silver iodide
Decreasing soluble
88
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
89
Disproportionation
A redox reaction in which the same element is both oxidised and reduced
90
Equation for the reaction of chlorine with water
Cl2 + H20 > HCl + HClO
<
(Reversible)
91
Where is an equilibrium established between in the reaction between chlorine and water
The chlorine, water, hydrochloric acid and chloric (I) acid
92
What is chlorine in the reaction between the reaction of chlorine and water
Both oxidised and reduced
93
How can chlorine be detected
Very pale green colour
94
How can hydrochloric acid be detected
Turns universal indicator paper red
95
How can chloric (I) acid be detected
Universal indicator paper red then bleached white
96
What happens to the chloric acid that is formed from the reaction between chlorine and water
Decomposes to hydrochloric acid and oxygen
97
Equation for decomposition of chloric (I) acid
2HClO > 2HCl + O2
98
What is the reaction between chlorine and water accelerated by
Sunlight and certain catalysts
99
Why is the reaction between chlorine and water accelerated by sunlight
Breaks bonds so lowers activation energy
100
What is produced when chlorine reacts with water in the presence of sunlight
Hydrochloric acid and oxygen
101
What is the benefit of using chlorine in water treatment
It kills bacteria
102
What is the risk in using chlorine in water treatment
It's toxic
| Chlorinated hydrocarbons are carcinogenic
103
What does the reaction of chlorine with cold dilute sodium hydroxide solution produce
Sodium chloride, sodium chlorate (I) and water
104
Equation for reaction between chlorine and sodium hydroxide solution
Cl2 + NaOH > NaCl + NaClO + H2O
105
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
106
Why is the reaction between chlorine and sodium chloride a disproportionation reaction
Chlorine is both oxidised and reduced
107
Main use of sodium chlorate
Domestic bleach
