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.
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.
The physical state of the halogens at room temperature
- The halogens become darker as you go down the group.
- Chlorine is pale green, bromine is red-brown and iodine is black.
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.
- 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.
- 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.
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.
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)
- 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.
- 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.
Sodium donates its outer electron to chlorine forming the metal halide salt NaCl