Group 7

• what are features of fluorine - pale yellow - gas at room temp - most electronegative
• what are features of chlorine - green gas - gas at room temp - toxic
• what are features of bromine - red-brown - liquid at room temp - poisonous and corrosive
• what are the features of iodine - grey colour - solid at room temp - sublimes easily
• what are the key physical properties - diatomic - all have s2p5 outer electrons - non polar - have low solubility in water - but dissolve easily in organic substances ie hexane
• what is the trend in atomic radii atomic radii increases down the group as outer electron shells are further from the nucleus due to more electrons and greater shielding so reduces the attraction to the nucleus
• what is the trend in melting and boiling points down the group 7 increases down the group as more electrons meaning more london forces between molecules so more energy is required to overcome
• what is the trend in reactivity in group 7 - reactivity decreases down the group as there is a decreasing tendency to gain electrons - increasing nuclear charge due to greater no of protons should attract outer electrons more but more electron shells so greater shielding and increase in atomic radii so harder to gain electrons as less posiitive nuclear charge in experienced by outer electrons
• what is electron affinity the ability to attract electrons - higher up the group
• what is the trend in electronegativity - decreases down group 7 - explanation as increasing nuclear charge due to greater no of protonsbut increasing no of electrons increases shielding and atomic radii so outer electrons experience less poitive nuclear charge so are harder to attract
• why is fluorine more significantly electronegative as lots of protons and small atomic radii and has no p orbital
• are halogens reducing or oxidising agents oxidising agents because accepts electrons forming negative ions
• what are displacement reactions - where a more reactive halogen displaces a less reactive one from its halide salt
• halogen - halide reactions - redox reactions, displacement reactions - substance displaced is oxidised and substance doing the displacing is reduced
• example of halogen halide reaction Cl2 + 2KBr ---- 2KCl + Br2
• solublity of halogens and colours of halides when dissolving in cyclohexane - all dissolve in non polar substances, as the soluter and solvent jave to have the same type of intermolecular forces/ attractions - only slightly soluble in water - in hexane - Cl = pale green - Br = orange - I = violet
• reaction with metals - react to form metal halides - usually redox reactions e.g. Mg + Cl2 ---- MgCl2
• reaction with water - a disproportionation reaction - e.g. Cl2 + H2O ---- HCl + HClO - HClO = hypochlorous acid - HClO + H2O --- ClO- + H3O - chlorate ions kills bacteria
• reaction with cold alkalis e.g. react with cold NaOH - Cl2 + 2NaOH ---- NaCl + NaOCl + H2O - disproportionation reaction - sodium chlorate is bleach
• reaction with hot alkalis e.g. with hot concentrated NaOH - 3Cl2 + 6NaOH ----- 5NaClO3 + H2O - disproportionation reaction
• reaction with phosphorus - forms phosphorus halides with limiting supply of HCl 3Cl2 + 2P ---- 2PCl3 with excess supply 5Cl2 + 2P ---- 2PCl5
• reaction with thiosulfate - both Cl and Br oxidise the sulfur e.g. 4Cl2 + S2O3 + 5H2O ---- 8Cl- + 2SO4 + 10H+
• what is the trend in reducing power down the group (halide ions) - increases down the group - halide ions can act as reducing agents - dependent on the attraction between the halides nucleus and valence electrons - down the group attraction is weaker as ionic radii increases so electrons further from the nucleus, more inner sheels so greater shielding
• reaction with sulfuric acid - form hydrogen halides - and usually steamy fumes
• what is the trend in melting and boiling points in hydrogen halides HF - higher mp as very electronegative so hydrogen bonds can form HCl to HI increasjng MP as more electrons so more londonnfirces to ivercome so more energy required
• reaction of water and hydrogen halides - hydrogen halides are acids e.g HCl + H2O -----> H3O + + Cl-
• reaction of hydrogen halides with ammonua ammonia js a base - HCl + NH3 ----> NH4Cl (misty white fumes)
• what is the test for hydrogen halides Method 1. add HNO3 ro remove any OH- or CO3- ions 2. add a few drops of sikver nitrate solution 3. add dilute ammonia 4. and if it doesnt dissolve add concentrated ammonja