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© Boardworks Ltd 20071 of 37. 2 of 37© Boardworks Ltd 2007.

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Presentation on theme: "© Boardworks Ltd 20071 of 37. 2 of 37© Boardworks Ltd 2007."— Presentation transcript:

1 © Boardworks Ltd of 37

2 2 of 37© Boardworks Ltd 2007

3 3 of 37 Group 7 – the halogens The elements in group 7 of the periodic table, on the right, are called the halogens. fluorine chlorine bromine iodine astatine I Br Cl F At

4 © Boardworks Ltd of 37 What are the halogens?

5 © Boardworks Ltd of 37 Why are they called the ‘halogens’? Halogens are very reactive non metals. They are all toxic or harmful because they are so reactive. Before antiseptics, iodine was used to clean wounds as it is harmful to all things, including bacteria. They are also never found free in nature because of their reactivity – they are found as compounds with metals. These halogen-metal compounds are salts, which give halogens their name – ‘halo-gen’ means ‘salt-former’.

6 © Boardworks Ltd of 37 All halogens have seven electrons in their outer shell. What is the electron structure of the halogens? fluorine 2,7 chlorine 2,8,7 bromine 2,8,8,7 They can easily obtain a full outer shell by gaining one electron. They have similar chemical properties. They all gain an electron in reactions to form negative ions with a -1 charge. This means that:

7 © Boardworks Ltd of 37 How do halogen molecules exist? All halogen atoms require one more electron to obtain a full outer shell and become stable. Each atom can achieve this by sharing one electron with another atom to form a single covalent bond. This means that all halogens exist as diatomic molecules: F 2, Cl 2, Br 2 and I 2. +  F F F F

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9 9 of 37 poisonous and smelly. brittle and crumbly when solid What are the general properties of the halogens? All the halogens are: They become darker in colour down the group: non-metals and so do not conduct electricity is pale yellow is green-yellow is blue-black. is red-brown

10 © Boardworks Ltd of 37 What is the physical state of the halogens? The melting and boiling points of the halogens increase down the group, as the molecules become bigger. Halogen Relative size Melting point (°C) Boiling point (°C) State gas liquid solid What is the state of each halogen at room temperature?

11 © Boardworks Ltd of 37 Melting and boiling points of halogens

12 © Boardworks Ltd of 37 Halogen vapours Bromine and iodine are not gaseous, but have low boiling points. This means that they produce vapour at relatively low temperature. They are volatile. Bromine produces some red-brown vapour, seen here above the liquid bromine in the jar. When iodine is heated gently, it changes directly from a solid to a gas without first becoming a liquid. This is called sublimation.

13 © Boardworks Ltd of 37 True or false?

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15 15 of 37 How do the halogens react with metals? The reactivity of halogens means that they readily react with most metals. Halogens need to gain electrons for a full electron shell and metals need to lose electrons for a full electron shell. This means that halogens and metals react to form ionic compounds. nickel (II) chloride copper (II) chloride These are metal halides, which are a type of salt.

16 © Boardworks Ltd of 37 What are halides? When halogens react with another substance, they become negative ions, as they are gaining an extra electron. The name of each of the halogens changes slightly once it has reacted – instead of ending with ‘–ine’, they end with ‘-ide’. HalogenHalidereaction fluoride (F - ) chloride (Cl - ) bromide (Br - ) iodide (I - ) (F) (Cl) (Br) (I) When this happens, they are called halides.

17 © Boardworks Ltd of 37 Halogens reacting with iron wool

18 © Boardworks Ltd of 37 What is the order of reactivity?

19 © Boardworks Ltd of 37 What is the reactivity of the halogens? The iron wool experiment shows that the reactivity of halogens decreases as you go down the group. decrease in reactivity Astatine is the halogen that appears directly below iodine in the periodic table. How do you think astatine would react with iron wool? Iron wool burns and glows brightly. Iron wool has a very slight glow. Iron wool glows but less brightly than with chlorine. Halogen Reaction with iron wool

20 © Boardworks Ltd of 37 Equations of halogens and iron When a halogen reacts with iron it forms an iron halide: What would the equation be for the reaction that forms iron (III) bromide? iron iron (III) chloride chlorine +  3Cl 2 (g)2Fe (s)2FeCl 3 (s) +  halogen + iron  iron (III) halide The word and chemical equations for the reaction between chlorine and iron are: iron iron (III) bromide bromine +  3Br 2 (g)2Fe (s)2FeBr 3 (s) + 

21 © Boardworks Ltd of 37 How does electron structure affect reactivity? The reactivity of alkali metals decreases going down the group. What is the reason for this? The atoms of each element get larger going down the group. This means that the outer shell gets further away from the nucleus and is shielded by more electron shells. The further the outer shell is from the positive attraction of the nucleus, the harder it is to attract another electron to complete the outer shell. This is why the reactivity of the halogens decreases going down group 7. decrease in reactivity F Cl Br

22 © Boardworks Ltd of 37 How do the halogens react with non-metals? Halogens also react with non-metals. For example, halogens react with hydrogen to create hydrogen halides. All hydrogen halides are gases. They dissolve easily in water and become strong acids. Unlike their reactions with metals, halogens share electrons with non-metals, and so react to form covalent compounds. hydrogen H chlorine Cl hydrogen chloride H Cl  +

23 © Boardworks Ltd of 37 Displacement of halogens If a halogen is added to a solution of a compound containing a less reactive halogen, it will react with the compound and form a new one. sodium chloride sodium fluoride chlorinefluorine ++  F 2 (aq)2NaCl (aq)2NaF (aq)Cl 2 (aq) ++  A more reactive halogen will always displace a less reactive halide from its compounds in solution. This is called displacement.

24 © Boardworks Ltd of 37 Displacement of halogens Why will a halogen always displace a less reactive halogen?

25 © Boardworks Ltd of 37 Cl - Displacement theory If a metal halide is mixed with a more reactive halogen, the extra electron will be transferred from the less reactive to the more reactive halogen. - sodiumchloride fluorine fluoride Na + Cl - F chlorine

26 © Boardworks Ltd of 37 Displacement reactions of halogens

27 © Boardworks Ltd of 37 Displacement reactions: summary The reactions between solutions of halogens and metal halides (salts) can be summarised in a table: 2KCl + I 2 2KBr + I 2 halogen chlorine bromine iodine salt (aq) potassium chloride potassium iodide potassium bromide 2KCl + Br 2 no reaction

28 © Boardworks Ltd of 37 Is there a displacement reaction?

29 © Boardworks Ltd of 37 Reactions of halogens: summary

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31 31 of 37 How many everyday uses of halogens can you see below? What are the uses of halogens?

32 © Boardworks Ltd of 37 What are the uses of halogens?

33 © Boardworks Ltd of 37 What are the uses of halogens?

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35 35 of 37 Glossary diatomic – Molecules that exist as two atoms covalently bonded together. displacement – The reaction when a more reactive halogen reacts with a compound containing a less reactive halogen. halide – The name of a halogen when it has reacted with another substance and gained a full outer electron shell. halogen – An element that belongs to group 7 of the periodic table. hydrogen halide – A compound formed from the reaction between hydrogen and a halogen. metal halide – A compound formed from the reaction between a metal and a halogen. sublime – To change from a solid to a gas without first becoming a liquid. volatile – A substance that evaporates or produces vapour at relatively low temperatures.

36 © Boardworks Ltd of 37 Anagrams

37 © Boardworks Ltd of 37 Multiple-choice quiz


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