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Boardworks GCSE Additional Science: Chemistry The Halogens

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Presentation on theme: "Boardworks GCSE Additional Science: Chemistry The Halogens"— Presentation transcript:

1 Boardworks GCSE Additional Science: Chemistry The Halogens

2 Boardworks GCSE Additional Science: Chemistry The Halogens

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

4 Boardworks GCSE Additional Science: Chemistry The Halogens
What are the halogens? Boardworks GCSE Additional Science: Chemistry The Halogens

5 Why are they called the ‘halogens’?
Boardworks GCSE Additional Science: Chemistry 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. Photo credit: Dr John Mileham Liquid bromine in a jar on the left, iodine on the right. 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?
Boardworks GCSE Additional Science: Chemistry 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 How do halogen molecules exist?
Boardworks GCSE Additional Science: Chemistry The Halogens 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. + F This means that all halogens exist as diatomic molecules: F2, Cl2, Br2 and I2.

8 Boardworks GCSE Additional Science: Chemistry The Halogens

9 What are the general properties of the halogens?
Boardworks GCSE Additional Science: Chemistry 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: is pale yellow is green-yellow is red-brown is blue-black.

10 What is the physical state of the halogens?
Boardworks GCSE Additional Science: Chemistry 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 -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
Boardworks GCSE Additional Science: Chemistry The Halogens

12 Boardworks GCSE Additional Science: Chemistry The Halogens
Halogen vapours Boardworks GCSE Additional Science: Chemistry The Halogens Bromine and iodine are not gaseous, but have low boiling points. This means that they produce vapour at relatively low temperature. They are volatile. Photo credit: Dr John Mileham 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 GCSE Additional Science: Chemistry The Halogens
True or false? Boardworks GCSE Additional Science: Chemistry The Halogens Teacher notes This true-or-false activity could be used as a plenary or revision exercise on halogens, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise.

14 Boardworks GCSE Additional Science: Chemistry The Halogens

15 How do the halogens react with metals?
Boardworks GCSE Additional Science: Chemistry The Halogens 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. Photo credit (left and right): Dr John Mileham nickel (II) chloride copper (II) chloride

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What are halides? Boardworks GCSE Additional Science: Chemistry The Halogens 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 (F) fluoride (F-) (Cl) chloride (Cl-) (Br) bromide (Br-) (I) iodide (I-)

17 Halogens reacting with iron wool
Boardworks GCSE Additional Science: Chemistry The Halogens Teacher notes This virtual experiment compares the reactivity of the halogens with iron wool. It could be used as a precursor to running the practical in the lab, or as a revision exercise. When using this activity, it should be made clear that with iodine, the reaction takes several minutes of strong heating before it reacts. This is illustrated by the stop watch, but is not run in real time. CA16_halogen_ironwool_experiment8_RM.swf

18 What is the order of reactivity?
Boardworks GCSE Additional Science: Chemistry The Halogens Teacher notes This matching activity could be used as a plenary or revision exercise on halogens and their reaction with iron wool. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.

19 What is the reactivity of the halogens?
Boardworks GCSE Additional Science: Chemistry The Halogens The iron wool experiment shows that the reactivity of halogens decreases as you go down the group. decrease in reactivity 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. Teacher notes Astatine is a rare, radioactive element that has a half-life of only 8 hours. Astatine is the halogen that appears directly below iodine in the periodic table. How do you think astatine would react with iron wool?

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

21 How does electron structure affect reactivity?
Boardworks GCSE Additional Science: Chemistry The Halogens 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 decrease in reactivity 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 How do the halogens react with non-metals?
Boardworks GCSE Additional Science: Chemistry The Halogens Halogens also react with non-metals. For example, halogens react with hydrogen to create hydrogen halides. chlorine Cl hydrogen chloride H Cl hydrogen H + 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 Displacement of halogens
Boardworks GCSE Additional Science: Chemistry The 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. sodium chloride sodium fluoride chlorine fluorine + F2 (aq) 2NaCl (aq) 2NaF (aq) Cl2 (aq) A more reactive halogen will always displace a less reactive halide from its compounds in solution.

24 Displacement of halogens
Boardworks GCSE Additional Science: Chemistry The Halogens Why will a halogen always displace a less reactive halogen?

25 Boardworks GCSE Additional Science: Chemistry The Halogens
Displacement theory Boardworks GCSE Additional Science: Chemistry The Halogens 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. Cl - - Na + Cl sodium chlorine chloride - F fluorine fluoride

26 Displacement reactions of halogens
Boardworks GCSE Additional Science: Chemistry The Halogens Teacher notes This virtual experiment illustrates how a more reactive halogen will displace a less reactive halogen. It could be used as a precursor to running the practical in the lab, or as a revision exercise.

27 Displacement reactions: summary
Boardworks GCSE Additional Science: Chemistry The Halogens The reactions between solutions of halogens and metal halides (salts) can be summarised in a table: salt (aq) potassium chloride potassium iodide potassium bromide halogen chlorine bromine iodine 2KCl + Br2 2KCl + I2 no reaction 2KBr + I2 no reaction no reaction

28 Is there a displacement reaction?
Boardworks GCSE Additional Science: Chemistry The Halogens Teacher notes This drag and drop activity provides the opportunity for informal assessment of students’ understanding of halogens and displacement.

29 Reactions of halogens: summary
Boardworks GCSE Additional Science: Chemistry The Halogens Teacher notes This completing sentences activity could be used as a plenary or revision exercise on the reactions of halogens. Students could be asked to write down the missing words in their books and the activity could be concluded by the completion on the IWB.

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31 What are the uses of halogens?
Boardworks GCSE Additional Science: Chemistry The Halogens How many everyday uses of halogens can you see below? Teacher notes This illustration contains several discussion points relating to the uses of halogens including: Non-stick frying pan Polymers of fluorine are used to make the non-stick on frying pans. Toothpaste Fluoride is used in toothpaste to prevent tooth decay. In animal food supplements Iodine is used in animal food supplements. In insecticides Bromine is used in insecticides. In antiseptics Iodine and chlorine are used as antiseptics. In medicines. Bromine is used in the pharmaceutical industry to make medicines.

32 What are the uses of halogens?
Boardworks GCSE Additional Science: Chemistry The Halogens

33 What are the uses of halogens?
Boardworks GCSE Additional Science: Chemistry The Halogens Teacher notes This matching activity could be used as a plenary or revision exercise on halogens and their uses. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.

34 Boardworks GCSE Additional Science: Chemistry The Halogens

35 Boardworks GCSE Additional Science: Chemistry The Halogens
Glossary Boardworks GCSE Additional Science: Chemistry The Halogens 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.

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Anagrams Boardworks GCSE Additional Science: Chemistry The Halogens

37 Boardworks GCSE Additional Science: Chemistry The Halogens
Multiple-choice quiz Boardworks GCSE Additional Science: Chemistry The Halogens Teacher notes This multiple-choice quiz could be used as a plenary activity to assess students’ understanding of halogens. The questions can be skipped through without answering by clicking “next”. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.


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