Group 7(17), the halogens common mistakes

Common mistakes

• Confusing trends in electronegativity and boiling point

  Stating that electronegativity increases down the group.

  Fix itRemember that electronegativity decreases down Group 7 due to increased atomic size and shielding.

• Confusing oxidising and reducing agents

  Students often confuse oxidising agents with reducing agents.

  Fix itRemember that oxidising agents gain electrons and are reduced, while reducing agents lose electrons and are oxidised.

• Confusing reactivity order

  Students often confuse the reactivity of halogens, thinking that bromine can displace chlorine.

  Fix itRemember that reactivity decreases down the group; chlorine is more reactive than bromine.

• Incorrectly balancing ionic equations

  Students often forget to balance the charges in ionic equations.

  Fix itEnsure that both the number of atoms and the total charge are balanced on both sides of the equation.

• Confusing the colors of precipitates

  Students often confuse the colors of the precipitates formed by different halide ions.

  Fix itRemember that chloride gives a white precipitate, bromide gives a cream precipitate, and iodide gives a yellow precipitate.

• Confusing chlorine with chloramine

  Students often confuse chlorine with chloramine, which is a different compound used in water treatment.

  Fix itRemember that chlorine is a strong disinfectant, while chloramine is a more stable compound formed when chlorine reacts with ammonia, used for longer-lasting disinfection.

• Confusing products of disproportionation

  Students often confuse the products formed during the disproportionation of chlorine in water and alkali.

  Fix itRemember that in water, chlorine forms hypochlorous acid and chloride ions, while in alkali, it forms hypochlorite and chloride ions.

• Confusing chlorine with chlorinated compounds

  Students often confuse chlorine gas (Cl2) with chlorinated organic compounds.

  Fix itRemember that chlorine gas is a disinfectant, while chlorinated compounds are by-products that can be harmful.