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Halogens Halogens

Halogens - PowerPoint Presentation

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Halogens - PPT Presentation

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

potassium chlorine bromine reactive chlorine potassium reactive bromine hydrogen reactions halogens ide reaction fluorine iron colour acid description halogen

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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