The periodic table and identification of ionsPresentation Transcript
The Periodic Table andIdentification of Ions and GasesIGCSE Grade 10 Chemistry
What you need to be able to do and understand:Group properties Identification of ions and gases Describe lithium, sodium and potassium Use the following tests to identify: in Group I as a collection of relatively soft Aqueous cations: metals showing a trend in melting point and reaction with water. ammonium, copper(II), iron(II), iron(III) and zinc by means of aqueous Predict the properties of other elements sodium hydroxide and aqueous in Group I, given data where appropriate. ammonia as appropriate. (Formulae of Describe the trends in properties of complex ions are not required.) chlorine, bromine and iodine in Group VII Anions: including colour, physical state and reactions with other halide ions. carbonate by means of dilute acid and then limewater, Predict the properties of other elements in Group VII, given data where chloride by means of aqueous silver appropriate. nitrate under acidic conditions,Transition elements nitrate by reduction with aluminium, Describe the transition elements as a sulfate by means of aqueous barium collection of metals having high ions under acidic conditions densities, high melting points and Gases: forming coloured compounds, and which, as elements and compounds, often act ammonia by means of damp red as catalysts. litmus paper,Noble gases carbon dioxide by means of limewater, Describe the noble gases as being chlorine by means of damp litmus unreactive. paper, Describe the uses of the noble gases in hydrogen by means of a lighted splint, providing an inert atmosphere, i.e. argon oxygen by means of a glowing splint in lamps, helium for filling balloons.
Trends of group I the alkali metals Physical properties: -good conductors -very soft (a knife can cut them) -low density (they float) -low melting and boiling points Chemical properties: -all react with H2O but with increasing reactivityMetal This metal is silvery and Density (g/cm3) Melts at (°C) Reactivity with waterLi soft 0.53 181 Floats and fizzes Increasing Shoots across water reactivityNa a little softer 0.97 Density 98 Melting Softness increases increases pointK softer still 0.86 63 decreases Melts with heat and H2 catches fireRb even softer 1.53 39 Watch the YouTube video.Cs the softest 1.88 29 Watch the YouTube video. Make a prediction for Fr (the last in this group)- what are the trends? WHY?
Why do we see these trends?Why do the elements in group I all react in a similar way? Atoms with the same number of valency electrons react in a similar way.Why does reactivity increase down group I? In reactions, the group I atoms lose their outer electron, to gain a stable outer shell. The more shells there are, the further the outer electron is from the positive nucleus – so the easier to lose. The easier it is to lose an electron, the more reactive the metal. Li Na K How do Rb and Cs react with water?
Trends of group VII the halogens General information: -form coloured gases -are poisonous -form diatomic molecules Reactivity DECREASES as you go down the group.Halogen At room temperature Boiling point (°C) Reactivity with iron woolF2 a yellow gas -188 Iron wool burst into flame as fluorine passes Colour gets Boiling over it – without any heating deeper and pointCl2 a green gas -35 Hot iron wool glows brightly decreasing density increases increases reactivityBr2 a red liquid 59 Hot iron wool glows but less brightlyI2 a black solid 184 Hot iron wool shows a faint red glow Make a prediction for At (the last in this group)- what are the trends? WHY?
Why do we see these trends?Why do the elements in group VII all react in a similar way? Atoms with the same number of valency electrons react in a similar way.Why does reactivity decrease down group VII? Halogen atoms react to gain or share an electron. The positive nucleus of the atom attracts the extra electron. The more shells there are, the further the outer shell is from the nucleus. So attracting an electron becomes more difficult. So reactivity falls. F Cl Br
Trends of group o the noble gases General information: -unreactive -form coloured gases -are non-metals -are monoatomicNoble Size and mass of atom Boiling point (°C) A balloon full of this gasgasHe -269 rises quickly into the airNe Increase -246 Boiling rises slowly Density in size pointAr and mass -186 increases falls slowly increasesKr -152 falls quicklyXe -107 falls very quickly Make a prediction for Rn (the last in this group)- what are the trends? WHY?
Why do we see these trends?Why are the elements in group o unreactive? Atoms have no need to react in order to gain or lose electrons. They are already have a stable outer electron shell.Why does density increase down group o? The Noble gases grow denser („heavier‟) down the group because the mass of the atoms increases. The increasing boiling points is a sign of increasing attraction between atoms. It gets harder to separate them to form a gas. He Ne Ar
What are some uses of noble gases? Because they are unreactive they are safe to use. When a current is passed through them they glow. Gas Uses Helium -it is lighter than air it is used to fill balloons and airships, it does not catch fire Argon -as a filler in light bulbs -protect metals that are being welded (does not react) Neon -advertising signs, glows red but colour can be changed if mixed with other gases Krypton -lasers (eye surgery) -car headlights Xenon -gives a light similar to daylight but with a blue tinge -car headlights, lighthouse lights, operating rooms Somechemistry fun
The transition elements Physical properties: -hard, tough and strong -high melting points -malleable and ductile -good conductors of heat and electricity -high density Chemical properties: -most from coloured compounds -they are much less reactiveSome data for some transition metals than group I or II metals with sodium as a comparison. -most can form ions with variable chargesElement Density (g/cm3) Melting point (°C) -can form more than oneFe 7.9 1535 compound with anotherCu 8.9 1083 elements (because of the variable charge) e.g. FeONi 8.9 1455 and Fe2O3Na 0.97 98 -from complex ions
What are some uses of transitionelements? Used in structures such as bridges, building and cars as alloys– they are strong! Many transition elements act as catalysts – e.g. manganese dioxide (MnO2) in the breakdown of hydrogen peroxide.Because you love these chemistry songs so much!
Testing for ions Cations are positive Tests for cations Anions are negative Cation Test Result if positive ammonium add aqueous NH4+ sodium hydroxide -ammonia gas produced (red litmus paper turns blue) (NaOH) copper(II) -a pale blue precipitate forms Cu2+ -dissolves on adding more ammonia giving a deep blue colour iron(II) add aqueous -a pale green precipitate forms Fe2+ sodium hydroxide iron(III) (NaOH) or aqueous ammonia (NH3) -a red-brown precipitate forms Fe3+ zinc -a white precipitate forms Zn2+ -dissolves on adding more NaOH or NH3 giving a colourless solutionYou need to NH4+ Zn2+ Cu2+ Fe2+ Fe3+know the test Cu2+ in NH3but not the (pale blue) andformulae of Cu2+ in excess NH3 (dark blue)complex ions.
Testing for ions Cations are positive Anions are negative Tests for anions Anion Test Result if positivecarbonate -add dilute acid (HCl) and then -mixture bubbles and turns limewater CO32- limewater milky chloride -add dilute acid (nitric acid) and -a white precipitate forms Cl- aqueous silver nitrate -add sodium hydroxide nitrate -ammonia gas produced (red litmus (NaOH), then reduction with NO3- paper turns blue) aluminium sulfate -add dilute acid (HCl) and then -a white precipitate forms SO42- aqueous barium nitrate Cl2+ SO42- NO3- CO32-You need to knowthe test but not theformulae ofcomplex ions.
Testing for You need to know the test but notgasesTests for gases the formulae of complex ions. Gas Test Result if positive ammonia -damp red litmus -red litmus paper turns blue (NH3) papercarbon dioxide -add limewater -turns limewater milky (CO2) -blue litmus paper turns red chlorine -damp litmus paper -universal litmus paper turn red (Cl2) -then both are bleached white hydrogen -a lighted splint -goes “pop” (H2) oxygen -a glowing splint -splint bursts into flame (O2) NH3 CO2 Cl2 O2 H2