Group 7 Elements in the Halogen Group Fluorine F Chlorine Cl Bromine Br Iodine I Astatine At Group 7 Elements Similar reactions to with other elements because they all gain one electron ID: 302150
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Slide1
Halogens
Group 7Slide2
Elements in the Halogen Group
Fluorine (F)
Chlorine (
Cl
)
Bromine (Br)
Iodine (I)
Astatine (At)Slide3
Group 7 Elements
Similar reactions to with other elements because they all gain one electron.
All react with metals to form compounds called halides.Fluorine is the most reactive halogen, and the reactivity decreases as you go down the group.They are diatomic (Cl2
Fl
2
, they always exist in pairs) Slide4
Properties of Halogens
Need to learn!
Element
Symbol
State at
room temperature
ColourFluorineF
GasPale YellowChlorineCl
GasYellow-GreenBromineBrLiquid
Red-Brown
Iodine
I
Solid
GreySlide5
Equations for Reactions of Halogens with Metals
You just saw iron reacting with chlorine, can you write a word equation for this reaction?
What might the symbol equation for this reaction be?
Iron + Chlorine
Iron chloride
Fe + Cl
2
FeCl3
Is this balanced?
2Fe + 3Cl
2
2FeCl
3Slide6
Some More Examples
(Ide at the end when combined)
Potassium + Chlorine Potassium Chloride
Calcium +
Bromine Calcium Chloride Slide7
Halogens and
hydrogen (Used to make acids)
The halogens react with hydrogen gas to form halogen halides. These form acids when they dissolve in water.
For example:
hydrogen (g)
+fluorine (g) → hydrogen fluoride (g)
H2 + F2 → 2HFWhen hydrogen fluoride dissolves in water it makes hydrofluoric acid, HF(
aq)(aq) means aqueous – Latin for dissolved in waterSlide8
Your turn
Write word and balanced symbol equations for the reactions of hydrogen with
a) chlorine
b) bromine
Which acids are formed from a) and b)?Slide9
Answers
a)
hydrogen (g) + chlorine(g) →
hydrogen
chloride
(g)
H2 + Cl2 → 2HCl
b) hydrogen (g) + bromine(g) → hydrogen bromide (g) H2 + Br2
→ 2HBr2. Hydrochloric acid, hydrobromic acidSlide10
Hydrofluoric acid
All the acids just named are extremely hazardous.
Hydrofluoric acid is used in
etching glass. It has the following
hazard symbols.
What do they mean?Slide11
Example of burns from HF acid, from a home glass polisher kit.
When we say wear goggles, we really mean it.
Toxic and corrosive. It is absorbed through the skin and bonds to calcium in your bones!Slide12
Some elements are more reactive than others. A reactive metal will displace (take the place of) a less reactive one to form a compound.
For example:
Iron + copper sulphate → iron sulphate + copperWhich is the more reactive metal, iron or copper
?
Iron!!
Displacement reactionsSlide13
Displacement Reactions of Halogens
These can be used to work out how reactive the different halogens are.
A more reactive halogen will displace a less reactive halogen from its compounds.In the example below chlorine is more reactive than bromine, so chlorine displaces bromine from a bromide.Potassium Iodide + Chlorine Potassium Chloride + IodineSlide14
The order of reactivity of the halogens is:
Fluorine
Chlorine
Bromine
Iodine
Astatine
Reactivity decreasesSlide15
Balanced symbol Equations
NB, remember the halogens are
diatomic molecules
this means that in their natural state they are so reactive that they exist as two atoms joined together.
Chlor
ine
+ potassium bromide → potassium
chloride + bromine (
red-brown
)
Cl
2
+ 2KBr
→
2K
Cl
+ Br
2
Chlor
ine
+ potassium
iod
ide
→ potassium
chlor
ide
+
iodine
(brown/purple)
Cl
2
+
2KI
→
2K
Cl
+
I
2
Brom
ine
+ potassium iod
ide
→ potassium
brom
ide
+ iod
ine
Br
2
+
2KI
→
2K
Br
+
I
2Slide16
Exam question
(c) When
chlorine is added to a solution of potassium bromide, a colour change is seen. When chlorine is added to a solution of potassium fluoride, no colour change is seen.Explain how these observations provide evidence for the order of reactivity of bromine, chlorine and fluorine. (6 marks)Slide17
*(c)
A explanation to include some of the following points • colour change shows reaction occurs • chlorine reacts with potassium bromide solution • bromine is formed • colour is red brown • chlorine displaces bromide ions • chlorine is more reactive than bromine • no colour change shows no reaction / chlorine does not react with potassium fluoride solution • chlorine does not displace fluoride ions • chlorine is less reactive than fluorine • order of reactivity from most reactive halogen is fluorine, chlorine, bromine
Level
1
1 - 2
• a limited description of at least two relevant points either from one reaction or from both reactions • the answer communicates ideas using simple language and uses limited scientific terminology • spelling, punctuation and grammar are used with limited accuracy
2
3 - 4
• a detailed description of one reaction (one minor omission may be ignored) / a limited description of some aspects of both reactions • a detailed description of one reaction (one minor omission may be ignored) / a limited description of some aspects of both reactions • spelling, punctuation and grammar are used with some accuracy
3
5 - 6
• a detailed description of both reactions (one minor
ommision
may be ignored) • the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately • spelling, punctuation and grammar are used with few errors