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1 of 43© Boardworks Ltd 2009
2 of 43© Boardworks Ltd 2009 Starter Write down everything you know about the elements in group 7.
3 of 43© Boardworks Ltd 2009 Group 7 Elements: Redox Reactions Lesson Objectives: Explain the trend in boiling points of Cl 2, Br 2 and I 2. Explain the trend in reactivity for the Group 7 elements. Describe the redox reactions of the Group 7 elements with other halide ions. Describe and interpret, using oxidation numbers, the reaction of chlorine with water and aqueous sodium hydroxide. Key Words: reactivity, displacement reaction, disproportionation, precipitation reaction
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5 of 43© Boardworks Ltd 2009 What are the halogens? The halogens are the elements in Group 7 of the periodic table. The name halogen comes from the Greek words for salt-making.
6 of 43© Boardworks Ltd 2009 Group 7 Elements: The Halogens Physical Properties: Low melting and boiling points Exist as diatomic molecules On descending the group, no. of electrons increases increasing van der Waals’ forces between molecules. Boiling points increase on descending the group. The physical states of the halogens at room temperature; Gas Liquid Solid On descending the group
7 of 43© Boardworks Ltd 2009 Physical properties of halogens
8 of 43© Boardworks Ltd 2009 Trends in boiling point Halogen molecules increase in size down the group. This leads to greater van der Waals forces between molecules, increasing the energy needed to separate the molecules and therefore higher melting and boiling points. fluorine atomic radius = 42 × 10 -12 m boiling point = -118 °C iodine atomic radius = 115 × 10 -12 m boiling point = 184 °C van der Waals forces
9 of 43© Boardworks Ltd 2009 Trends in electronegativity Electronegativity of the halogens decreases down the group due to an increase in atomic radius. fluorine atomic radius = 42 × 10 -12 m electronegativity = 4.0 iodine atomic radius = 115 × 10 -12 m electronegativity = 2.5 Increased nuclear charge has no significant effect because there are more electron shells and more shielding. Iodine atoms therefore attract electron density in a covalent bond less strongly than fluorine.
10 of 43© Boardworks Ltd 2009 Astatine The name astatine comes from the Greek word for unstable. It was first made artificially in 1940, by bombarding 209 Bi with -radiation. What do you predict for these properties of astatine? Astatine exists in nature in only very tiny amounts. It is estimated that only 30 grams of astatine exist on Earth at any one time. This is because it is radioactive, and its most stable isotope ( 210 At) has a half-life of only 8 hours. electronegativity. state at room temperature colour
11 of 43© Boardworks Ltd 2009 Halogens: true or false?
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13 of 43© Boardworks Ltd 2009 Group 7 Elements: Electron Configuration ElementElectron Configuration F[He]2s 2 2p 5 Cl[Ne]3s 2 3p 5 Br[Ar]4s 2 4p 5 I[Kr]5s 2 5p 5 At[Xe]6s 2 6p 5 7 electrons in the outer shell, highest energy electrons in a p sub-shell Each element has two fewer electrons than the next noble gas Outer p sub-shell containing 5 electrons (needs 1 more to form a - 1 ion)
14 of 43© Boardworks Ltd 2009 The Halogens: Oxidising Agents The halogens are the most reactive non-metals in the periodic table Strong oxidising agents (they gain electrons) Oxidising power decreases down the group. Therefore less reactive down the group ½ Cl 2 (g) + e - Cl - (g) ( - 1 oxidation state) Reactivity decreases down the group because; Atomic radius decreases Electron shielding increases Ability to gain an electron decreases
15 of 43© Boardworks Ltd 2009 Reactions of the halogens Halogens react with metals such as sodium and iron: They also take part in displacement reactions with halide ions, such as the reaction that is used to make bromine from potassium bromide in seawater: halogen + hydrogen hydrogen halide They also react with non-metals such as hydrogen: halogen + sodium sodium halide chlorine + potassium bromide potassium chloride bromine +
16 of 43© Boardworks Ltd 2009 Reaction with iron
17 of 43© Boardworks Ltd 2009 Reactions with hydrogen Chlorine and hydrogen explode in bright sunlight but react slowly in the dark. The halogens react with hydrogen gas to product hydrogen halides. For example: Cl 2(g) + H 2(g) 2HCl (g) Iodine combines partially and very slowly with hydrogen, even on heating. Bromine and hydrogen react slowly on heating with a platinum catalyst.
18 of 43© Boardworks Ltd 2009 Redox reactions of halogens
19 of 43© Boardworks Ltd 2009 What is the reactivity of the halogens? The reactions of the halogens with iron and hydrogen show that their reactivity decreases down the group. How do you think fluorine and astatine would react with iron wool and hydrogen? Iron wool burns and glows brightly. Iron wool has a very slight glow. Iron wool glows but less brightly than with chlorine. chlorine bromine iodine HalogenReaction with iron woolReaction with hydrogen Explodes in sunlight, reacts slowly in the dark. Reacts slowly on heating with catalyst. Reacts partially and very slowly.
20 of 43© Boardworks Ltd 2009 Electron structure and reactivity
21 of 43© Boardworks Ltd 2009 Halogen displacement reactions
22 of 43© Boardworks Ltd 2009 Halogen displacement reactions
23 of 43© Boardworks Ltd 2009 Halogen displacement reactions Halogen displacement reactions are redox reactions. Cl 2 + 2KBr 2KCl + Br 2 To look at the transfer of electrons in this reaction, the following two half equations can be written: Chlorine has gained electrons, so it is reduced to Cl - ions. What has been oxidized and what has been reduced? 2Br - Br 2 + 2e - Cl 2 + 2e - 2Cl - Bromide ions have lost electrons, so they have been oxidized to bromine.
24 of 43© Boardworks Ltd 2009 Oxidizing ability of halogens fluorine increasing oxidizing ability iodine bromine chlorine In displacement reactions between halogens and halides, the halogen acts as an oxidizing agent. This means that the halogen: What is the order of oxidizing ability of the halogens? is reduced to form the halide ion. gains electrons oxidizes the halide ion to the halogen
25 of 43© Boardworks Ltd 2009 The Halogens: Recognising them The halogens form solutions with different colours. A colour change will show if a reaction has taken place. HalogenWatercyclohexane Cl 2 Pale-green Br 2 Orange I2I2 Brownviolet If you shake the reaction mixture with an organic solvent it can help distinguish between halogens that have reacted
26 of 43© Boardworks Ltd 2009 Oxidizing ability of halogens
27 of 43© Boardworks Ltd 2009 Chlorine and disproportionation
28 of 43© Boardworks Ltd 2009 Reaction of chlorine with water Chlorination of drinking water raises questions about individual freedom because it makes it difficult for individuals to opt out. Chlorine is used to purify water supplies because it is toxic to bacteria, some of which can cause disease. Adding it to water supplies is therefore beneficial for the population. However, chlorine is also toxic to humans, so there are risks associated with gas leaks during the chlorination process. There is also a risk of the formation of chlorinated hydrocarbons, which are also toxic.
29 of 43© Boardworks Ltd 2009 Bleach and the chlorate(I) ion Household bleach commonly contains the chlorate(I) ion, ClO -, in the form of sodium chlorate(I), NaOCl. ClO - + H 2 O + Cl - + 2OH - The chlorine has been reduced because it has gained electrons. Its oxidation state has decreased from +1 in ClO - to –1 in Cl -. How many electrons are needed to balance this equation? The chlorate(I) ion behaves as an oxidizing agent. It oxidizes the organic compounds in food stains, bacteria and dyes. Has the chlorine been oxidized or reduced in the reaction? 2e -
30 of 43© Boardworks Ltd 2009 Redox reactions of chlorate ions
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32 of 43© Boardworks Ltd 2009 Uses and Halide Tests Lesson Objectives: Interpret and make predictions from the chemical and physical properties of the Group 7 elements/compounds. Contrast the benefits and risks of chlorine’s use as a water treatment. Describe the precipitation reactions of aqueous anions Cl–, Br– and I– with aqueous silver ions, followed by aqueous ammonia. Recognise the use of these precipitation reactions as a test for different halide ions. Key Words: reactivity, displacement reaction, disproportionation, precipitation reaction
33 of 43© Boardworks Ltd 2009 Halides When halogens react with metals, they form compounds called halides. Many naturally-occurring halides have industrial, household and medical applications. caesium chloride sodium hexafluoroaluminate titanium(IV) chloride lithium iodide potassium bromide HalideFormulaUses CsCl NaAlF 6 TiCl 4 LiI KBr Extraction and separation of DNA Electrolysis of aluminium oxide Extraction of titanium Electrolyte in batteries Epilepsy treatment in animals
34 of 43© Boardworks Ltd 2009 Identifying halide ions Halides can be identified by their reaction with acidified silver nitrate solution to form silver halide precipitates. Silver chloride has a low solubility in water, so it forms a white precipitate: the positive result in the test for chloride ions. KCl (aq) + AgNO 3(aq) KNO 3(aq) + AgCl (s) potassium chloride silver chloride + potassium nitrate silver nitrate +
35 of 43© Boardworks Ltd 2009 Identifying halide ions
36 of 43© Boardworks Ltd 2009 Identifying halide ions
37 of 43© Boardworks Ltd 2009 Uses of halides in photography Silver halides are used in photography. Ag + + e - Ag Photographic film coated with a silver halide is exposed to light, causing the halide to decompose to form silver. This appears as a black precipitate on the photographic film. light mask paper coated in silver halide silver precipitate white paper under mask
38 of 43© Boardworks Ltd 2009 William Fox Talbot William Fox Talbot (1800–1877) was a British scientist and mathematician. He was one of the key figures in the development of the use of silver halides in photography. Fox Talbot adapted the process by removing any unreacted silver halide by washing with sodium thiosulfate solution. This meant that the print could be used repeatedly in the way that photographic negatives can be today. A French scientist called Louis Daguerre developed the use of silver halides on copper plates. These were effective at producing prints, but could only be used once.
39 of 43© Boardworks Ltd 2009 Hydrogen halides The hydrogen halides are colourless gases at room temperature. Hydrogen fluoride has an unexpectedly high boiling point compared to the other hydrogen halides. This is due to hydrogen bonding between the H–F molecules. Hydrogen halideBoiling point (°C) HF HCl HBr HI 20 -85 -67 -35
40 of 43© Boardworks Ltd 2009 Halides as reducing agents A substance that donates electrons in a reaction (i.e. is oxidized) is a reducing agent because it reduces the other reactant. fluoride increasing reducing ability iodide bromide chloride The larger the halide ion, the easier it is for it to donate electrons and therefore the more reactive it is. This is because its outermost electrons are further from the attraction of the nucleus and more shielded from it by other electrons. The attraction for the outermost electrons is therefore weaker.
41 of 43© Boardworks Ltd 2009 Halides: true or false?
42 of 43© Boardworks Ltd 2009 Sodium halides and sulfuric acid The sodium halides react with concentrated sulfuric acid. The reactions of sodium halides with concentrated sulfuric acid demonstrate the relative strengths of the halide ions as reducing agents. During this reaction two things can happen to the sulfuric acid. It can act as an acid. be reduced
43 of 43© Boardworks Ltd 2009 Sodium halides and sulfuric acid
44 of 43© Boardworks Ltd 2009 Sodium halides and sulfuric acid
45 of 43© Boardworks Ltd 2009 Oxidation states
46 of 43© Boardworks Ltd 2009 Sodium halides and sulfuric acid
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48 of 43© Boardworks Ltd 2009 Glossary
49 of 43© Boardworks Ltd 2009 What’s the keyword?
50 of 43© Boardworks Ltd 2009 Multiple-choice quiz
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Halogens. Objectives Be able to... Recall the main properties and trends of the Halogens Explain trends using knowledge of intermolecular bonding and.
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Lesson Objectives: Describe the Periodic Table in terms of the arrangement of elements by increasing atomic number, in periods and in groups. Explain.
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.
2.7 Inorganic chemistry of group 7 (limited to chlorine, bromine and iodine) Cro2012.
Halogens All toxic All form Diatomic molecules All form ionic salts Group VII.
Halogens AS. F Cl Br I (At) Generally: Oxidising agents Germicides Note: Atoms are halogens Ions are halides Ions have 8 electrons by borrowing one, so.
TOPIC 3 - PERIODICITY IB CHEMISTRY SL DESCRIBE THE ARRANGEMENT OF ELEMENTS IN THE PERIODIC TABLE IN ORDER OF INCREASING ATOMIC NUMBER The elements.
© Boardworks Ltd of 34 KS4 Chemistry Halogens.
Group 7 Elements The Halogens. Group 7 – the halogens The elements in group 7 of the periodic table, on the right, are called the halogens. fluorine chlorine.
What do we know about fluorine, chlorine and bromine? 1) 2) 3) 4)
HALOGENS. Electron structure and reactivity HHe Rn Xe Kr Ar Ne RaAcRfDbSgBhHsMtDsRg??????? BaLaHfTaWReOsIrPtAuHgTlPbBiPoAt SrYZrNbMoTcRuRhPdAgCdInSnSbTeI.
Group 7, the Halogens. Group 7—The Halogen Group All the elements in Group 7 are nonmetals except for astatine 2 2 These elements are called halogens,
11.0 The Halogens Text book p166 to AQA AS Specification LessonsTopics 1 How and why does the atomic radius and electronegativity change in Gp.
SL Topic 3 Periodic Trends Wichita East High School Beth McKee The Periodic Table – p. 11 IB Diploma book.
GROUP 17 ELEMENTS 1.Group 17 Elements 2. Physical Properties of Halogens 3. Reactivity of Group 17 Elements 4. Chemical Properties of Group 17 Elements.
They have low meting and boiling points. The atoms within each molecule are held together by strong covalent bonds, but the forces between the molecules.
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Explain, in terms of electrons, why potassium reacts more violently than sodium. (3 marks) bigger atom or outer shell electron further from nucleus or.
In this presentation you will: Properties of an Atom explore the reactivity series explore the bonding of atoms Next > explore the reactivity of different.
Chapter 6 The Periodic Table: Group7 6.1 The Halogens 6.2 Reactions of The Halogens and Their Ions.
Periodicity is a regular periodic variation of properties of elements with atomic number and positions in the periodic table.
GROUP VII The Halogens National 5 Chemistry KNOCKHARDY PUBLISHING.
Halogens To know how the Group 7 elements behave. (Grade C) To know how the properties of the Group 7 elements change down the group. (Grade B) To explain.
GROUP VII The Halogens A guide for iGCSE students KNOCKHARDY PUBLISHING 2010 SPECIFICATIONS.
Angstrom Care 1www.AngstromCare.com Angstrom Care Halogens II.
The Halogens A group of non metal elements. State at room temperature Chlorine is a yellow – green gas Bromine is a red - brown liquid which easily evaporates.
Trends in the Periodic Table trend: direction or pattern p
© Boardworks Ltd 2003 THE HALOGENS. © Boardworks Ltd 2003 Halogens and the Periodic Table These are the Halogens or Group 7 Elements H Li Na K Rb Cs Fr.
Revision part3 Periodicity. Aims Electronegativity Ionisation energies Atomic radii Boiling points Group 2 redox reactions Group 2 oxides with water Thermal.
Group 7, the Halogens. Group 17—The Halogen Group All the elements in Group 17 are nonmetals except for astatine, which is a radioactive metalloid. Representative.
ELECTROLYSIS. What is a redox reaction? Oxidation is the addition of oxygen to a substance and reduction is the removal of oxygen from a substance. lead.
Topic 3 Periodicity SL + HL. 3.1 The periodic table of the elements The elements are arranged in order of increasing atomic number, reading from left.
Chapter 11 Groups II and VII Physical Properties of Group II Elements The elements of group 2 are referred to as the ALKALINE EARTH METALS Electronic.
Periodicity Elements in the PT are arranged in order of increasing atomic number. Elements in the same group - same chemical and physical properties.
IGCSE CHEMISTRY SECTION 2 LESSON 2. Content The iGCSE Chemistry course Section 1 Principles of Chemistry Section 2 Chemistry of the Elements Section 3.
Can you draw Bohr diagrams for flourine and chlorine onto your worksheet?
Learning Objectives General trends of group 17 elements Chemical properties of group 17 elements Oxoacids of group 17 elements.
Trends in the Periodic Table (Chpt. 7). 1. Atomic radius (size) 2. Ionization energy 3. Electronegativity The three properties of elements whose changes.
Chemical Properties Discuss the similarities and differences in the chemical properties of elements in the same group. Q – What are chemical.
Keywords: proton, neutron, electron, shells, negative, atomic number, mass number C2 Topic 1 Atomic Structure and the Periodic Table This topic looks at:
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Redox Reactions and Oxidation States. The Basics... ‘Redox’ is used to describe reactions where oxidation and reduction take place. If one reactant.
Title: Lesson 3 Chemical Properties Learning Objectives: –Understand the following trends in reactivity: Alkali metals with water Alkali metals with halogens.
Periodic Table Quiz What is the lightest element on the periodic table? How many elements are there? What is the name for columns? What is the name for.
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