Properties of the Group 7 Elements

  • The halogens are the Group 7 non-metals that are poisonous and include fluorine, chlorine, bromine, iodine and astatine.
  • Halogens are diatomic, meaning 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.
  • Fluorine and Chlorine are both gases at room temperature.
  • Bromine is a red-brown liquid and iodine is a black crystalline solid which undergoes sublimation .

Physical Properties

Physical Properties Table, IGCSE & GCSE Chemistry revision notes

Trends in Group 7

Melting and Boiling Point

  • The melting and boiling points of the halogens increase as you go down the Group.
  • This is due to increasing intermolecular forces as the atoms become larger, so more energy is required to overcome these forces.

Melting & boiling points of the Halogens, IGCSE & GCSE Chemistry revision notes

Graph showing the melting and boiling points of halogens

State at Room Temperature

  • At room temperature (20 °C), the physical state of the halogens changes as you go down the Group.
  • Chlorine is a gas, bromine is a liquid and iodine is a solid.

States of the Halogens, IGCE & GCSE Chemistry revision notes

The physical state of the halogens at room temperature

Colour

  • The halogens become darker as you go down the group.
  • Chlorine is pale green, bromine is red-brown and iodine is black.

Colours of the Halogens, IGCSE & GCSE Chemistry revision notes

The colours of the halogens

Predicting Properties of the other halogens (Fluorine and Astatine)

Melting and Boiling Point

  • The melting and boiling point of the halogens increases as you go down the Group.
  • Fluorine is at the top of Group 7 so will have the lowest melting and boiling point.
  • Astatine is at the bottom of Group 7 so will have the highest melting and boiling point.

Physical States

  • The halogens become harder as you go down the Group.
  • Fluorine is at the top of Group 7 so will be a gas.
  • Astatine is at the bottom of Group 7 so will be a solid.

Colour

  • The colour of the halogens becomes darker as you go down the Group.
  • Fluorine is at the top of Group 7 so the colour will be lighter, so fluorine is yellow.
  • Astatine is at the bottom of Group 7 so the colour will be darker, so astatine is black.

Reactions of the Group VII Elements

Electronic Configuration and Reactivity in Group VII

  • Reactivity of Group 7 non-metals increases as you go up the Group.
  • Each outer shell contains seven electrons and when they react, they will need to gain one outer electron to get a full outer shell of electrons.
  • As you go up Group 7, the number of shells of electrons decreases (Period number decreases moving up the Periodic Table).
  • This means that the outer electrons are closer to the nucleus so there are stronger electrostatic forces of attraction that attract the extra electron needed.
  • This allows an electron to be attracted more readily, so the higher up the element is in Group 7 then the more reactive it is.

Group 7 element electronic configurations, IGCSE & GCSE Chemistry revision notes

The electronic configuration of the first three elements in Group VII

Reaction with Halide Ions

  • A halogen displacement reaction occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide.
  • The reactivity of Group 7 non-metals increases as you move up the Group
  • Out of the 3 halogens, chlorine, bromine and iodine, chlorine is the most reactive and iodine is the least reactive

Chlorine and bromine

  • If you add chlorine solution to colourless potassium bromide solution, the solution becomes orange as bromine is formed.
  • Chlorine is above bromine in Group 7 so it is more reactive.
  • Chlorine will therefore displace bromine from an aqueous solution of metal bromide.

Potassium Bromide + Chlorine → Potassium Chloride + Bromine

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

Bromine and iodine

  • Bromine is above iodine in Group 7 so it is more reactive.
  • Bromine will therefore displace iodine from an aqueous solution of metal iodide.

Bromine + Magnesium Iodide → Magnesium Bromide + Iodine

Br2(l) + 2MgI (aq) → 2MgBr (aq) + I2(aq or s)

Non-metal Halides

  • The halogens react with non-metals via covalent bonding to form simple molecular structures.
  • They react with hydrogen to form hydrogen halides.
  • The reactions are less vigorous as we move down the group due to the decrease in reactivity of the halogens.
  • Chlorine which is higher up the group forms a hydrogen halide in the presence of sunlight:

CH4 + Cl2 → CH3Cl + HCl

  • Bromine requires a higher temperature for a hydrogen bromide to form.
  • Halogens below bromine would require a much higher temperature to form their respective hydrogen halides.
  • Those above chlorine would react more vigorously.
  • Other compounds include CCl4, HF and PCl5.

Metal Halides

  • The halogens react with some metals to form ionic compounds which are metal halide salts.
  • The halide ion carries a -1 charge so the ionic compound formed will have different numbers of halogen atoms, depending on the valency of the metal.
  • E.g. sodium is a Group 1 metal:

2Na + Cl2 → 2NaCl

  • Calcium is a Group 2 metal:

Ca + Br2 → CaBr2

  • The halogens decrease in reactivity moving down the group but they still form halide salts with some metals including iron.
  • The rate of reaction is slower for halogens which are further down the group such as bromine and iodine.

Ionic bonding – Sodium Chloride, IGCSE & GCSE Chemistry revision notes

Sodium donates its outer electron to chlorine forming the metal halide salt NaCl

AQA GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.