Revision part3 Periodicity

Aims Electronegativity Ionisation energies Atomic radii Boiling points Group 2 redox reactions Group 2 oxides with water Thermal decomposition Group 7 properties Displacement reaction of grp 7 Testing for halide ions Uses of Cl

Electronegativity A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond On your periodic table draw this trend

Ionisation energies 1 st IE the energy required to remove on electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions. 3 factors that influence IE 1.The distance of the outermost electron from the nucleus (atomic radius) 2.Electron shielding 3.Nuclear charge

Atomic radii Number of protons increases; shielding stays the same Radius decreases Radius increases Extra shells and more shielding outweigh additional protons in the nucleus

Boiling points: they are related to structure Giant structuresMolecular structures NaMgAlSiP4P4 S8S8 Cl 2 Strong forces between atoms Weak van der Waals forces between molecules MetallicCovalentVan der Waals High melting pointsLow melting points Good conductorsPoor conductors

Group 2 redox reactions Identify what is being oxidised and what is being reduced Mg + O 2  2MgO O has gained electrons Mg has lost electrons Oxidation numbers

Group 2 with oxygen Reactivity increases down the group. This is explained by the increasing ease with which group 2 elements form the corresponding 2+ ion. Mg + ½ O 2  MgOburns with a bright white flame Ca + ½ O 2  CaOburns with a brick-red colour Sr + ½ O 2  SrOburns with a crimson colour Ba + ½ O 2  BaOburns with a green colour

Group 2 with water Group 2 elements also undergo a redox reaction with water Oxidation numbers Mg + 2H 2 O  Mg(OH) 2 + H 2 The rate of reaction increases down the group, largely due to the ease of cation formation

Group 2 oxides with water All group 2 metal oxides react with water to form hydroxides: MgO + H 2 O  Mg(OH) 2 They are not redox reactions. The oxidation numbers stay the same Ca(OH) 2 neutralize soil and lakes Mg(OH) 2 antacids

Thermal decomposition of group 2 carbonates Group 2 carbonates decompose to form oxides and carbon dioxide MgCO 3  MgO + CO 2 The ease at which a carbonate decomposes decreases down a group Again they are not redox reactions

GROUP TRENDS INCREASES down Group increased size makes the van der Waals forces increase more energy is required to separate the molecules F2F2 Yellow Cl2Cl2 Green Br 2 Red/brown I2I2 Grey GAS LIQUIDSOLID Colour State (at RTP) APPEARANCE BOILING POINT F2F Cl2Cl Br 2 58 I2I2 183Boiling point / ° C

HALOGENS - DISPLACEMENT REACTIONS THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS... A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE HALIDES ARE SALTS FORMED FROM HALOGENS A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE e.g.CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE CHLORINE + SODIUM IODIDE IODINE + SODIUM CHLORIDE BROMINE + SODIUM IODIDE IODINE + SODIUM BROMIDE BUTBROMINE + SODIUM CHLORIDE CHLORINE + SODIUM BROMIDE (Bromine is below chlorine in the Group so is less reactive)

SODIUM CHLORIDE DISPLACEMENT REACTIONS - EXPERIMENT HALOGENS - DISPLACEMENT REACTIONS CHLORINE SODIUM BROMIDESODIUM IODIDE Solution stays colourless NO REACTION Solution goes from colourless to orange- yellow NO REACTION Solution goes from colourless to orange- yellow BROMINE FORMED Solution goes from colourless to orange- yellow NO REACTION Solution goes from colourless to red IODINE FORMED BROMINE Solution goes from colourless to orange- red IODINE FORMED

OTHER REACTIONS OF CHLORINE Water Halogens react with decreasing vigour down the group as their oxidising power decreases Litmus will be turned red then decolourised in chlorine water C l 2 (g) + H 2 O (l) HC l (aq) + HOC l (aq) strong acid bleaches by oxidation This is an example of DISPROPORTIONATION … ‘simultaneous oxidation and reduction of a species’ Alkalis Chlorine reacts with cold, aqueous sodium hydroxide. 2NaOH (aq) + C l 2 (g) —> NaC l (aq) + NaOC l (aq) + H 2 O (l)

TESTING FOR HALIDES – AgNO 3 CHLORIDEwhite ppt of AgClsoluble in dilute ammonia BROMIDEcream ppt of AgBrinsoluble in dilute ammonia but soluble in conc. IODIDEyellow ppt of AgIinsoluble in dilute and conc. ammonia solution halides precipitate as follows Ag + (aq) + X¯(aq) ——> Ag + X¯(s) when they dissolve in ammonia a colourless diammine complex is formed [Ag(NH 3 ) 2 ] + (aq)

PLACE A SOLUTION OF THE HALIDE IN A TEST TUBE CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3

ADD SOME DILUTE NITRIC ACID CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3

ADD SILVER NITRATE SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE AgC l CREAM PRECIPITATE OF SILVER BROMIDE AgBr YELLOW PRECIPITATE OF SILVER IODIDE AgI CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3

ADD CONCENTRATED AMMONIA SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE CREAM PRECIPITATE OF SILVER BROMIDE - SOLUBLE YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3

HALOGENS & HALIDES - USES Chlorine, C l 2 water purification bleach solvents polymers - poly(chloroethene) or PVC CFC’s Fluorine, F 2 CFC’s polymers - PTFE poly(tetrafluoroethene) as used in... non-stick frying pans, electrical insulation, waterproof clothing Fluoride, F¯ helps prevent tooth decay - tin fluoride is added to toothpaste - sodium fluoride is added to water supplies Hydrogen fluoride, HF used to etch glass Silver bromide, AgBr used in photographic film