Group seven elements (halogens) ASK ABT COLOURS

• all have diatomic molecules • all form X- ions • reactivity decreases as you go down the group • density increases as you go down the group • melting and boiling points increase as you go down the group • colour becomes darker as you go down the group • halogens can displace halogens that are lower down the group

• physical state at rt = gas • colour at rt = pale yellow

• physical state at rt = gas • colour at rt = yellow-green

• physical state at rt = liquid • colour at rt = brown liquid (brown gas when over bp)

• physical state at rt = solid • colour at rt = grey solid (purple vapour when over bp)

• atoms become larger (more shells) as you go down the group • this means that their relative molecular mass increases • covalent substances alr have high melting and boiling points due to their giant covalent lattice structure • as relative molecular mass increases, mp and bp does as well, as the intermolecular forces of attraction increase • this means that more heat energy is required to overcome these stronger intermolecular forces of attraction • so mp and bp increases down group

• each halogen atom has 7 electrons in their outer shell, so require 1 more electron to be gained to have a full outer shell and be stable • this causes two halogen atoms to share an electron each to form a more stable, covalent molecule that is more stable than the atom itself • so the halogens exist as diatomic molecules

• atoms increase in size as you go down the group • this means that the outermost shell gets increasingly further away from the nucleus as you go down the group • so the forces of attraction between the nucleus and outermost shell decrease as you go down the group • so electrons cannot be attracted and gained as easily as you go down the group therefore reactivity decreases as u go down grp 7

• fluorine is the most reactive halogen as its at the top of group 7 • astatine is the least reactive halogen as its at the bottom of group 7

• as density increases down the group - At would be a solid • as colour becomes darker down the group - At would be black or very darkly coloured • as mp and bp increases down the group - At would have the highest mp and bp of the halogens • as reactivity decreases down the group - At would be the least reactive halogen • as all halogens have diatomic molecules, astatine would be At2 • as reactivity decreases as you go down the group, astatine will be displaced from its compound by all other halogens

• displacement reactions occur between halogens when a more reactive halogen replaces a less reactive halide in a compound • the halide being displaced comes from a halogen that is lower in Group 7, so it is less reactive • the more reactive halogen replaces it and becomes the new halide in the compound

chlorine + potassium bromide => potassium chloride + bromine

Cl2 (aq) + 2KBr (aq) => 2KCl (aq) + Br2 (aq)

• brown liquid produced • this causes a colour change from colourless to brown

bromine + potassium iodide => potassium bromide + iodine

Br2 (aq) + 2KI (aq) => 2KBr (aq) + I2 (aq)

• brown liquid produced • this causes a colour change from colourless to brown

chlorine + potassium iodide => potassium chloride + iodine

Cl2 (aq) + 2KI (aq) => 2KCl (aq) + I2 (aq)

• brown liquid produced • this causes a colour change from colourless to brown

• hydrogen halides are produced • these can dissolve in water to produce acids e.g HCl - hydrochloric acid