Group 17 Elements with Halide Ions (DP IB Chemistry): Revision Note

Philippa Platt

Written by: Philippa Platt

Reviewed by: Richard Boole

Updated on

Group 17 Elements with Halide Ions

  • The halogens are the Group 17 non-metals

    • They are poisonous

    • They include fluorine, chlorine, bromine, iodine and astatine

Periodic table highlighting Group 7 elements: fluorine, chlorine, bromine, iodine, and astatine
The halogens are located on the right of the periodic table in the fifth column of the p block
  • Halogens are diatomic

    • This means that they form molecules of two atoms

  • All halogens have seven electrons in their outer shell

    • They form halide ions by gaining one more electron to complete their outer shells

Colours and states at room temperature

Halogen colours and states at room temperature:

  • Fluorine: yellow gas

  • Chlorine: pale green gas

  • Bromine: orange-brown liquid that readily evaporates to form a brown gas

  • Iodine: grey-black solid that sublimes to form a purple vapour

Four test tubes showing halogen states: fluorine gas (pale yellow), chlorine gas (green/yellow), bromine liquid (orange/brown), iodine solid (grey/black, purple vapour).
The halogens get darker in colour down Group 17

Colour of halogen solutions in water:

  • Fluorine: not typically tested due to its reactivity

  • Chlorine: green-blue solution

  • Bromine: orange solution

  • Iodine: dark brown solution

Physical properties of the halogens

  • The melting and boiling points of the halogens increase down the group

Graph to show the melting and boiling points of the halogens
The melting and boiling points increase down Group 17

Reactivity trend in Group 17

  • The reactivity of the halogens decreases down the group

  • Each halogen has an outer electron configuration of ns2np5

    • This means that they react by gaining one outer electron to achieve a full outer shell

  • Descending the group:

    • The atomic radius increases

    • The number of electron shells increases, causing shielding to increase

    • Electron affinity becomes less negative (less exothermic)

  • This results in:

    • The electrostatic forces of attraction between the nucleus and any incoming electron is weaker

    • So, the halogens become less reactive down the group

  • This decrease in reactivity reflects the decreasing non-metallic character of the elements

    • They become less effective at gaining electrons

Displacement reaction of the halogens with halide ions

  • A more reactive halogen will displace a less reactive halogen from an aqueous solution of its halide

  • The order of reactivity among chlorine, bromine and iodine is:

    • Chlorine > Bromine > Iodine

Example: chlorine displaces bromine

  • If you add pale green chlorine solution to colourless potassium bromide solution, the solution becomes orange as bromine forms

  • Chlorine is above bromine in Group 17 so it is more reactive

  • Chlorine will therefore displace bromine from an aqueous solution of a metal bromide

Cl2 (aq)  + 2KBr (aq) → 2KCl (aq) + Br2 (aq)

chlorine + potassium bromide → potassium chloride + bromine

Example: Bromine displaces iodine

  • If you add orange bromine solution to colourless sodium iodide solution, the solution becomes brown as iodine forms

  • Bromine is above iodine in Group 17 so it is more reactive

  • Bromine will therefore displace iodine from an aqueous solution of a metal iodide

Br2 (l) + 2NaI (aq) → 2NaBr (aq) + I2 (aq)

bromine +  sodium iodide → sodium bromide + iodine

Worked Example

Which of the statements below are correct?

I. Potassium chloride solution will react with fluorine to form chlorine.

II. Sodium chloride solution will react with iodine to form chlorine.

III. Lithium iodide solution will react with bromine to form iodine.

 

  A.  I and II only

  B.  I and III only

  C.  II and III only

  D.  I, II and III

 

Answer

  • The correct option is B

    • I is correct

      • Fluorine is above chlorine in Group 17 and will displace it

    • II is incorrect

      • Iodine is below chlorine and cannot displace it

    • III is correct

      • Bromine is above iodine and displaces it from lithium iodide

You've read 1 of your 5 free revision notes this week

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Philippa Platt

Author: Philippa Platt

Expertise: Chemistry Content Creator

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener

Richard Boole

Reviewer: Richard Boole

Expertise: Chemistry Content Creator

Richard has taught Chemistry for over 15 years as well as working as a science tutor, examiner, content creator and author. He wasn’t the greatest at exams and only discovered how to revise in his final year at university. That knowledge made him want to help students learn how to revise, challenge them to think about what they actually know and hopefully succeed; so here he is, happily, at SME.

Download notes on Group 17 Elements with Halide Ions