grp 7

• Fluorine (F2) is a very pale yellow gas that is highly reactive.
• Chlorine (Cl2) is a greenish, reactive gas that is poisonous in high concentrations.
• Bromine (Br2) is a red liquid that gives off dense brown/orange poisonous fumes.
• Iodine (I2) is a shiny grey solid that sublimes to a purple gas.
• Increase in melting point and boiling point as one goes down the group due to larger molecules and larger London forces.
• As the intermolecular forces get larger, more energy has to be put into overcoming the forces, increasing the melting and boiling points.
• Fluorine has a melting point of -220 degrees Celsius and a boiling point of -188 degrees Celsius, making it a gas.
• Chlorine has a melting point of 101 degrees Celsius and a boiling point of 35 degrees Celsius, making it a gas.
• Bromine has a melting point of 7 degrees Celsius and a boiling point of 59 degrees Celsius, making it a liquid.
• Iodine (I2) reacts with hydrogen gas to produce hydrogen iodide (HI).
• The general trend is that hydrides become less stable going down the group.
• The reactions of the elements with hydrogen decrease in speed and vigour going down the group.
• This can be explained by the decreasing size of the H-Hal bond energy going down the group.
• Hydrogen iodide is thermally unstable and will decompose if a hot nichrome wire is plunged into it, producing purple vapour of iodine.
• As the halogen atoms become bigger, their bond length is longer, and the bonding pair of electrons gets further from the halogen nuclei.
• All the halogens react with hydrogen gas to produce hydrogen halides.
• Iodine has a melting point of +114 degrees Celsius and a boiling point of 184 degrees Celsius, making it a solid.
• The test solution is made acidic with nitric acid, and then Silver nitrate solution is added dropwise.
• The reactions of iodide ions with H2SO4 involve three redox steps.
• Fluoride and Chloride ions react with concentrated sulfuric acid to form NaHSO4 and HF.
• Acid-base reactions occur between the solid halides and concentrated sulfuric acid.
• The role of nitric acid in the reaction of halide ions with silver nitrate is to react with any carbonates present to prevent formation of the precipitate Ag2CO3.
• The reactions of halide ions with silver nitrate are used as a test to identify which halide ion is present.
• H2SO4 acts as an acid in the first step producing HBr and then as an oxidising agent in the second redox step.
• Iodide ions are the strongest halide reducing agents and can reduce the sulfur from +6 in H2SO4 to 0 in S and -2 in H2S.
• The reactions of the solid halides with concentrated sulfuric acid are acid-base reactions and not redox reactions.
• The solid halides do not react with concentrated sulfuric acid due to the lack of redox reactions.
• Electronegativity is the relative tendency of an atom in a molecule to attract electrons in a covalent bond to itself.
• As one goes down the group, the electronegativity of the elements decreases.
• As one goes down the group, the atomic radii increases due to the increasing number of shells.
• The nucleus is therefore less able to attract the bonding pair of electrons.
• A halogen that is a strong oxidising agent will displace a halogen that has a lower oxidising power from one of its compounds.
• Oxidising agents are electron acceptors.
• Chlorine will displace both bromide and iodide ions; bromine will displace iodide ions.
• The colour of the solution in the test tube shows which free halogen is present in solution.
• All halide salt solutions, such as KI, NaBr, KCl, are colourless.
• The reaction of Br2 (l) with Mg (s) results in MgBr2 (s) and 2Na (l), and is reversed by 2Na (l) and 2Br (l).
• The benefits to health of water treatment by chlorine outweigh its toxic effects.
• If some universal indicator is added to the solution it will first turn red due to the acidity of both reaction products and then turn colourless as the HClO bleaches the colour.
• Chlorine is used in water treatment to kill bacteria and has been used to treat drinking water and the water in swimming pools.