Teacher notes Students could be asked to write balanced symbol equations for these reactions.
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 for 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.
Teacher notes Substances can obtain the activation energy they need to react from (sun)light. Halogens can also react with other non-metals. For example, fluorine is so reactive that it can even form bonds with the noble gases such as xenon. Xenon(II) fluoride (XeF 2 ) is made by the reaction of xenon and fluorine, using heat or electricity to provide the activation energy. It is used to etch patterns on silicon chips. If XeF 2 is heated, it reacts to form xenon(VI) fluoride, XeF 6 . XeF 4 also exists. The xenon fluorides are often used in exam question to test knowledge of molecular shapes. XeF 2 is linear, XeF 4 is square planar, and XeF 6 is octahedral. See the ‘ Structure and Shape ’ presentation for more information about molecular shapes.
Teacher notes Students should remember the mnemonic OILRIG – O xidation I s L oss of electrons; R eduction I s G ain of electrons. See the ‘ Redox reactions ’ presentation for more information about redox reactions and half equations.
Teacher notes Fluorine and hydrogen explode even in the dark at temperatures as low as -200°C. Fluorine and iron wool ignite immediately and burn more vigorously than chlorine and iron wool. The reactions of astatine would be expected to be similar to those of iodine but less vigorous.
Teacher notes See the ‘ Redox Reactions ’ presentation for more information about redox reactions.
Teacher notes Students could be encouraged to see the relative oxidizing ability of the halogens as their ability to accept electrons, relating it to the size, nuclear charge and shielding. Also they could connect this trend to the electronegativity values and with the electron structures of the ions.
Teacher notes The reaction of chlorine and water shown here is used in water purification: see slide 22 of this presentation. The reaction of sodium hydroxide and water shown here is used to make bleach: see slide 23 of this presentation.
Photo credit: Danvlchenko Iaroslav / Shutterstock.com Teacher notes Addition of fluoride to drinking water is also carried out in certain areas and there are debates about extending the practice. The main benefit is reduction of tooth decay. However, fluoride can cause dental fluorosis (flecks of white in the teeth which can turn brown) and critics have linked it to other, more serious, health problems.
Teacher notes The chlorate(I) ion reacts with acids to form chlorine. Care must therefore be taken to avoid bleach coming into contact with acids in the home because chlorine gas is toxic. The chlorate(I) ion is unstable. It decomposes to form chloride ions and the chlorate(V) ion, ClO 3 - : 3ClO - → 2Cl - + ClO 3 - This is another disproportionation reaction, in which the chlorine atoms are both oxidized from oxidation state +1 to +5 in ClO 3 - , and reduced to -1 in Cl - . The chlorate(V) ion is an oxidizing agent: ClO 3 - + 6H + + 6e - → Cl - + 3H 2 O Potassium and sodium chlorate, KClO 3 and NaClO 3 , are used in weedkillers. They can also be used to oxidize the sucrose molecules in jelly babies in a common demonstration.