8C Inorganic Chemistry of Group 7 - Edexcel IAS Chemistry (Unit 2)

Introduction

This section introduces the topic of organic chemistry and group 7 elements.

Organic Chemistry of Group 7 Elements

• The focus is on trends and properties of group 7 elements, including boiling and melting temperatures, physical state, electronegativity, and reactivity.

• Halogens are the atoms in group 7 while halides are the ions they form.

• The section will cover chlorine, bromine, and iodine to make predictions about other halogens.

Trends in Melting Point, Boiling Point, and Electronegativity

This section covers trends in melting point, boiling point, and electronegativity for group 7 elements.

Melting Point and Boiling Point Trends

• As we move down the group from top to bottom, melting and boiling points increase due to an increase in electrons leading to stronger intermolecular forces.

• All halogens exist as diatomic molecules with London forces being responsible for their intermolecular forces.

• Chlorine is a gas at room temperature while bromine is a liquid and iodine is a solid. However, all can form gases at higher temperatures or vaporization.

• Different colors of vapors are produced depending on which halogen is present. Bromine produces brown or orange vapors while iodine produces purple vapors.

Electronegativity Trends

• Electronegativity decreases as we move down the group due to larger elements having more electron shells leading to more shielding from outer electrons becoming less attracted to the nucleus.

• Decreasing electronegativity also explains decreasing reactivity down the group since smaller anions attract electrons more closely than larger ones.

Redox Reactions of Halide Ions

This section covers redox reactions of halide ions in aqueous solutions.

• Halogens are highly reactive and can form over 60 possible combinations when reacting with metals from group 1 and group 2.

• The section will cover general rules for these reactions.

Differences in Oxidation Numbers

This section covers differences in oxidation numbers for halogens.

• Halogens have a range of oxidation states, but the most common is -1.

• As we move down the group, higher oxidation states become more stable due to larger atomic radii leading to weaker attraction between the nucleus and outer electrons.

Specific Reactions of Halogens

This section covers specific reactions of halogens.

• Chlorine reacts with water to produce hydrochloric acid and hypochlorous acid.

• Bromine reacts with water to produce hydrobromic acid and hypobromous acid.

• Iodine does not react with water but can react with iodide ions to produce triiodide ions.

Predicting Reactivity

This section covers how to use knowledge about halogen reactions to predict reactivity.

• Reactivity depends on how closely halogens attract electrons so that they can be held closer to the nucleus. Smaller anions are more reactive than larger ones.

• Knowledge about specific reactions of chlorine, bromine, and iodine can be used to make predictions about other halogens.

Redox Reactions

This section discusses redox reactions and how halogens act as oxidizing agents.

Halogen Electron Transfer

• Halogens gain electrons, while metals lose electrons in redox reactions.

• The halogen acts as the oxidizing agent because it is reduced, while the metal is oxidized.

• The oxidation number of the halogen always goes from 0 to -1, while the oxidation number of the metal goes from 0 to +1 or +2.

Halide-Halogen Displacement Reactions

• A displacement reaction occurs when a more reactive halogen displaces a less reactive one from its compound.

• These reactions are examples of redox reactions where the halogen changes from 0 to -1 and the halide changes from -1 to 0.

• Chlorine is more reactive than bromine and iodine due to its small size and higher electronegativity.

Organic Solvents in Halide-Halogen Displacement Reactions

This section explains how organic solvents can be used in halide-halogen displacement reactions.

Using Organic Solvents

• Adding an organic solvent like cyclohexane can make it easier to see color changes during displacement reactions.

• Cyclohexane and water do not mix, so they form layers that allow for clearer color differentiation.

• In a typical test, chlorine appears brown, bromine appears orange, and iodine appears purple.

Chlorine's Special Properties

This section discusses chlorine's unique properties in disproportionation reactions.

Disproportionation Reactions

• Chlorine can undergo a disproportionation reaction where it is simultaneously oxidized and reduced.

• In the reaction of chlorine with water, chlorine appears in both products.

• It's important to be able to write the full equation, provide information about conditions, and identify which species is being oxidized and reduced.

Oxidation and Reduction Reactions

This section discusses the oxidation and reduction reactions of chlorine gas, HCL, and NaCl with cold or hot alkali.

Chlorine Gas Oxidation and Reduction

• Chlorine gas has an oxidation number of zero.

• When it reacts with hydrogen gas, it is reduced to an oxidation number of -1 to form HCL.

• When it reacts with sodium metal, it is oxidized to an oxidation number of +1 to form NaCl.

• Sodium hypochlorite (NaClO) can be used as a disinfectant.

Cold Alkali Reaction

• When chlorine gas reacts with cold alkaline (specifically sodium hydroxide), two salts are formed: NaCl and NaClO.

• The Roman numeral in NaClO indicates the oxidation number of the chlorine atom. It changes from 0 in Cl2 to -1 in NaCl and +5 in NaClO3.

Hot Alkali Reaction

• When chlorine gas reacts with hot alkaline, we get a different compound: NaCl and NaClO3.

• The oxidation numbers for Cl2, NaCl, and NaClO3 are 0, -1, and +5 respectively.

Halides' Reaction with Sulfuric Acid

This section discusses the reaction between halides (not halogens) and sulfuric acid.

Halides vs. Halogens

• Halogens act as oxidizing agents while halides act as reducing agents.

• Iron halides react as reducing agents.

Reducing Power of Halides

• As we go down the group from fluorine to iodide, the reducing power increases.

• The extent of reduction depends on the reducing agent used.

Sulfuric Acid

• Concentrated sulfuric acid can be partially ionized.

• It works as an oxidizing agent and an acid.

• When it is reduced, three possible products are formed: SO2, S, and H2S.

Half Equations

• There are three different half equations depending on the extent of reduction.

• The oxidation number of sulfur in H2SO4 is +6.

Reduction of Halides

In this section, the speaker discusses the reduction of halides and how different halides produce different products.

Reduction of Halides

• Hydrogen ions and electrons are involved in the reduction process.

• Different halides produce different observations when reduced.

• Sodium iodide produces all three reduction products due to its high reducing power.

Reaction with NaCl

• When NaCl is reacted with sulfuric acid, hydrogen chloride is formed, producing messy fumes.

Reaction with NaBr

• When NaBr is reacted with sulfuric acid, hydrogen bromide is formed, which acts as a reducing agent to form bromine and SO2.

• HBr can undergo another redox reaction to form bromine and SO2.

Reaction with NaI

• When NaI is reacted with sulfuric acid, HI is formed, which acts as a base. HI then undergoes a redox reaction to form SO2, sulfur, and H2S.

• The equation for the oxidation of HI to form H2S involves reacting it with hydrogen ions and electrons.

Overall, the speaker explains how different halides produce different products when reduced. They provide specific examples for reactions involving NaCl, NaBr, and NaI. The notes also include equations for each reaction discussed.

Halides and Chemical Tests

In this section, the speaker discusses how to identify halide ions using chemical tests. They explain that silver halide compounds can be used to identify the presence of halide ions due to their low solubility, and that aqueous ammonia can be used to distinguish between chloride, bromide, and iodide ions.

Identifying Halides with Silver Nitrate

• Halides can be identified using silver nitrate solution.

• A white precipitate indicates the presence of chloride ions.

• A cream precipitate indicates the presence of bromide ions.

• A yellow precipitate indicates the presence of iodide ions.

Distinguishing Between Halides with Aqueous Ammonia

• Aqueous ammonia can be used to distinguish between chloride, bromide, and iodide ions.

• Dilute or concentrated aqueous ammonia is added after adding silver nitrate solution.

• The precipitate dissolves for chloride ions in both dilute and concentrated aqueous ammonia.

• The precipitate dissolves for bromide ions only in concentrated aqueous ammonia.

• The precipitate does not dissolve for iodine ions in either dilute or concentrated aqueous ammonia.

Hydrogen Halides Reacting with Water

• Hydrogen halides react with water to form colorless acidic solutions.

• Hydrofluoric acid undergoes partial ionization or dissociation due to its weak acidity.

Diffusion of Gases and Redox Reactions

The section covers the reaction to form ammonium chloride from ammonia and hydrochloric acid, diffusion of gases, identification of redox reactions using oxidation numbers, and a pathway progression question.

Ammonia and Hydrochloric Acid Reaction

• When forming ammonium chloride from ammonia and hydrochloric acid, heavier neon codes solid forms closer to HCL.

• NHD can move further and faster than NH3.

Redox Reactions

• None of the last five slaves that we've been looking at for different other reactions are redox reactions because the halide has stayed an oxidation number of minus 1.

• Identify redox reactions using oxidation numbers.

Pathway Progression Question

• Iodine can be obtained from iodine compounds such as potassium iodide by the reaction with coding. This is an example of a displacement action.

• Write the ionic equation for the formation of iodine by adding codn't aqueous potassium iodide.

• Potassium iodide + chlorine gas → potassium chloride + iodine

• Two iodide ions reacting with coating gas → Iodine solids (I2) + two chloride ions

• The color for iodine is purple.

Chemistry of Good Sun: Silver Nitrate Solution

The section covers silver nitrate solution added to an aqueous solution containing two different halide ions, identifying one possible halide ion that remains after adding concentrated ammonia solution, and identifying one possible halide ion that dissolves completely after adding concentrated ammonia solution.

Halide Ion Identification

• When silver nitrate solution is added to an aqueous solution containing two different halide ions, precipitate A remains while precipitate B dissolves completely after adding concentrated ammonia solution.

• Precipitate A does not dissolve after adding concentrated ammonia solution, which can only be iodide or I -.

• Identify by name or formula one possible halide and B.

• One possible halide for precipitate A is iodine (I -).

• Two possible answers for precipitate B are chloride (CL -) or bromide (BR -).

Concentrated Sulfuric Acid and Potassium Chlorate

In this section, we learn about the reaction that occurs when concentrated sulfuric acid is added to potassium chlorate. We also learn about the formula of the steamy fumes produced in this reaction.

Steamy Fumes Formula

• Concentrated sulfuric acid is added to potassium chlorate.

• A potential deducing reaction happens, but because it's potassium chloride, H2SO4 acts only as an acid rather than an oxidizing agent.

• The steamy fumes formed are HCl gas (hydrogen chloride).

• The equation for this reaction is: H2SO4 + KCl → KHSO4 + HCl or K2SO4 + 2HCl.

Oxidation Number of Sulfur and Ionic Equation

• When concentrated sulfuric acid is added to potassium bromide, a redox reaction occurs.

• The products formed include sulfur as the only reduction product.

• The oxidation number of sulfur in sulfuric acid is +6 and in sulfur dioxide is +4.

• The ionic equation for the redox reaction involves h2so4 reacting with hydrogen ions and bromine ions to form two products: bromine (Br2) and sulfur dioxide (SO2).

• To balance the equation, we need two bromide ions and two water molecules.

Redox Reaction with Potassium Iodide

• When concentrated sulfuric acid is added to potassium iodide, a redox reaction occurs.

• Two additional reduction products are formed besides SO2: solid yellow sulfur (S) and hydrogen sulfide gas (H2S).

• Sulfur has a yellow color as a solid while hydrogen sulfide smells like rotten eggs.

• The ionic equation for the redox reaction involves h2so4 reacting with hydrogen ions and iodine ions to form two products: bromine (Br2) and sulfur dioxide (SO2).

Conclusion

In this section, we conclude the topic on organic chemistry of group seven. We are encouraged to practice writing out ionic equations and try some questions from the textbook.

• We have covered all aspects of topic 8cv in organic chemistry of group seven.

• Writing out ionic equations can be tricky, so it's important to practice.

• It's also recommended that we read through the textbook and try some questions.

• If there are any questions, feel free to leave a comment below.