Group 7 – the halogens

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

4. What are the halogens?

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

7. F F + F F  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 diatomicmolecules:F2, Cl2, Br2 and I2.

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

10. 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 Melting point (°C) Boiling point (°C) State Relative size -220 -118 gas -101 -34 gas -7 59 liquid 114 184 solid What is the state of each halogen at room temperature?

11. Melting and boiling points of halogens

12. When iodine is heated gently, it changes directly from a solid to a gas without first becoming a liquid. This is called sublimation. 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.

13. True or false?

15. 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. These are metal halides, which are a type of salt. nickel (II) chloride copper (II) chloride

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

17. Halogens reacting with iron wool

18. What is the order of reactivity?

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

20. halogen + iron  iron (III) halide iron (III)chloride iron (III)bromide + + bromine chlorine iron iron   + + 3Cl2(g) 3Br2(g) 2Fe(s) 2Fe(s)   2FeCl3(s) 2FeBr3(s) Equations of halogens and iron When a halogen reacts with iron it forms an iron halide: The word and chemical equationsfor the reaction between chlorine and iron are: What would the equation be for the reaction that forms iron (III) bromide?

21. decrease in reactivity 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. F • This means that the outer shell gets further away from the nucleus and is shielded by more electron shells. Cl • 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. Br • This is why the reactivity of the halogens decreases going down group 7.

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

23. sodiumchloride sodiumfluoride + + fluorine  chlorine + + F2(aq) 2NaCl(aq)  2NaF(aq) Cl2(aq) 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. This is called displacement. A more reactive halogen will alwaysdisplace a less reactive halide from its compounds in solution.

24. Displacement of halogens Why will a halogen always displace a less reactive halogen?

25. + - Na Cl Cl - - F 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. chlorine sodium chloride fluorine fluoride

26. Displacement reactions of halogens

27. salt (aq) potassiumchloride potassiumbromide potassiumiodide halogen chlorine bromine iodine Displacement reactions: summary The reactions between solutions of halogens and metal halides (salts) can be summarised in a table: 2KCl + Br2 2KCl + I2 no reaction 2KBr + I2 no reaction no reaction

28. Is there a displacement reaction?

29. Reactions of halogens: summary

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

32. What are the uses of halogens?

33. What are the uses of halogens?

35. 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 withanother 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. Anagrams

37. Multiple-choice quiz