Group VII Properties (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

• These are the Group VII non-metals that are poisonous and include fluorine, chlorine, bromine, iodine and astatine
• Halogens are diatomic, meaning they form molecules of two atoms
  • The formulae of the halogens are F₂, Cl₂, Br₂, I₂ and At₂
• All halogens have seven electrons in their outer shell
• They form halide ions by gaining one more electron to complete their outer shells
• Fluorine is not allowed in schools so observations and experiments tend to only involve chlorine, bromine and iodine

Properties of the halogens

• At room temperature (20 °C), the physical state of the halogens changes as you go down the group
• Chlorine is a pale yellow-green gas, bromine is a red-brown liquid and iodine is a grey-black solid
• This demonstrates that the density of the halogens increases as you go down the group:

The physical state of the halogens at room temperature

• Reactivity of Group 7 non-metals increases as you go up the group (this is the opposite trend to that of Group I)
• Each outer shell contains seven electrons and when the halogen reacts, it 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, which help to 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

Diagram showing the electronic configuration of the first three elements in Group 7

Exended tier only

• You may be given information about some elements and asked to predict the properties of other elements in the group 
• The information you might be given could be in relation to melting/boiling point or physical state/density so it is useful to know the trends in properties going down the group

Predicting 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

Predicting physical states

• The halogens become denser 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

Predicting 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