group- 7 (Halogens)

• they have low metling and boiling points

  the melting and boiling point increases as you go down the group.
• they are poor conductors of heat and electricity
• the reactivity decreases as you go down the group because the outer electrons are further away from the nucleus
• their atom gain an electron in their outermost shell. going down the group the outermost shells get further away from the attractive force of the nucleus so it is harder to attract and gain an extra incoming electrons
• the outer shell will also be shielded by more inner shells of electron

  again reducing electrostatic force of attraction of the nucleus for an incoming electron
• therefore electrons are easier for the larger atoms to lose going down a group and harder for them to gain going down a group