2C Atomic Structure, Reactions and Compounds

Transcription

1 2C Atmic Structure, Reactins and Cmpunds Atmic Structure, Reactins and Cmpunds All substances cntain atms. All atms cntain sub-atmic particles and different atms cntain different numbers f these particles. The principal sub-atmic particles are prtns, neutrns and electrns. Why and hw substances react is related t their atmic structure. Basic Atmic Structure Atm: the smallest particle f matter that can exist by itself The atm cnsists f a very small, dense central cre called the nucleus The nucleus cnsists f prtns and neutrns All atms have electrns rbiting the nucleus in shells Lithium Atm Sub-atmic Particle Mass Charge Lcatin Prtn 1 atmic mass unit Psitive (1+) In Nucleus Neutrn 1 amu N chrge (neutral) In Nucleus Electrn amu Negative (1-) Orbiting the Nucleus Atmic Number: the number f Prtns in a nucleus Neutral Atm: atms are neutral because they have the same number f prtns and electrns and s their charges cancel ut Number f Electrns = Atmic Number Number f Neutrns = Mass Number Atmic Number 23 Mass Number Number f Prtns plus Neutrns 11 P and 12 N Na Symbl Sdium 11 Atmic Number Number f prtns (and electrns) 11 P (6 e - ) 40 Mass Number Number f Prtns plus Neutrns 20 P and 20 N Ca Symbl Calcium 20 Atmic Number Number f prtns (and electrns) 20 P (20 e - ) 14 Mass Number Number f Prtns plus Neutrns 7 P and 7N N Symbl Nitrgen 7 Atmic Number Number f prtns (and electrns) 7 P (7 e - ) 35 Mass Number Number f Prtns plus Neutrns 7 P and 18 N Cl Symbl Chlrine 17 Atmic Number Number f prtns (and electrns) 17 P (17 e - ) Electrnic Structure This describes the arrangement f electrns in shells arund the nucleus The electrns are placed in shells starting frm the shell nearest the nucleus and mving ut t the next shell nce that shell is full First Shell can hld up t 2 electrns Secnd Shell can hld up t 8 electrns Third shell can hld up t 8 electrns The remainder g int the furth shell Bhr Mdel f Atm Bhr Diagram: a diagram shwing the arrangement f electrns in an atm Sdium Na 1 Bhr Diagram f a Sdium Atm

2 2C Atmic Structure, Reactins and Cmpunds Mre Bhr Diagrams Aluminium Calcium Hydrgen Oxygen Nen Istpes: atms f an element which have the same number f prtns but different numbers f neutrns Carbn 12 Carbn 14 Nble Gases D nt react They each have a full uter shell f electrns This makes them very stable (unreactive) Bnding Mlecule: a grup f atms chemically jined r the smallest particle f a cmpund that shws the prperties f that cmpund When atms bnd they are trying t get a full uter shell S that they will be stable like the nble gases There are tw types f bnds used when frming cmpunds Inic Bnds One type f atm lses electrns t get a full uter shell and becmes psitively charged The ther type f atm gains electrns t get full uter shell and becmes negatively charged These tw ppsite charges attract each ther and frm an inic bnd In: is an atm (r grup f atms) with a charge Examples f Inic Bnds Sdium Chlride - NaCl Magnesium Oxide - MgO 2

3 2C Atmic Structure, Reactins and Cmpunds Cvalent Bnds Atms share electrns in pairs, ne electrn frm each atm, t get a full uter shell Examples f Cvalent Bnds Nte The inner electrn shells have been left ut t make things clearer. Yu d nt have t draw them Prperties f Inic and Cvalent Substances Cvalent Cmpunds Made f mlecules Usually Liquids r slids Lw melting and biling pints Usually insluble in water D nt cnduct electricity Inic Cmpunds Made f ppsitely charged ins Usually crystalline slids High melting and biling pints Usually sluble in water Cnduct electricity when mlten r disslved in water Investigate the Ability f Inic and Cvalent Substances t Cnduct Electricity Set up the apparatus as shwn Pur in a cvalent cmpund (e.g. pure water) Clse the switch and recrd what happens Result: the bulb des nt light Empty the apparatus and replace with an inic cmpund (e.g. salt slutin) Clse the switch and recrd what happens Result: the bulb lights Empty the apparatus and repeat with a number f inic and cvalent cmpunds Cnclusin: inic substances cnduct electricity when in slutin and cvalent substances d nt. Rusting and Crrsin Rusting as a chemical prcess in which irn becmes a new cmpund: irn xide Rust flakes ff expsing mre irn Rusting needs water and xygen The presence f salt makes rusting wrse 3 Flaking Rust

4 2C Atmic Structure, Reactins and Cmpunds Demnstrate that Oxygen and Water are Necessary fr Rusting Set up the apparatus as shwn Tube A has bth xygen and water Tube B has n water as calcium chlride absrbs any water present Tube C has n xygen as biling remves the xygen and the il stps any getting back int the water Result: nail in test tube A rusts. B and C dn t rust Cnclusin: xygen and water are bth needed fr rusting Preventing Rusting Rusting is prevented by keeping either water r xygen r bth away frm the irn Paint: keeps ut air and water Oil: keeps ut air and water Galvanising: i.e. cvering with a layer f zinc, keeps ut air and water Metals Alkali Metals Grup I f the Peridic Table They have similar prperties because they all have ne electrn in their uter shell They are sft and can be cut with a knife When fresh they have a metallic lustre (sheen) They react rapidly with air and quickly tarnish (turn dull) each frming its xide e.g. sdium + xygen = sdium xide They react rapidly with water frming hydrgen and a hydrxide Lithium + water lithium hydrxide and hydrgen (fast) Sdium + water sdium hydrxide and hydrgen (very fast) Ptassium + water Ptassium hydrxide and hydrgen (extremely fast, ften catches fire and may explde) Stred under il t prevent reactin with air and water As yu g dwn the grup they becme mre reactive Ptassium and water reacting Alkaline Earth Metals The elements f Grup II are the alkaline earth metals They are less reactive than the alkali metals The Reactin between Zinc and HCl, and a Test fr Hydrgen Place sme dilute hydrchlric acid in a test tube Add a little zinc Place yur thumb lightly ver the muth f the test tube and wait a cuple f minutes Result: the test tube fills with hydrgen gas Test: place a lighted taper t the muth f the test tube. Result: the gas burns with a squeaky pp Cnclusin: the gas is hydrgen Zn + 2HCl ZnCl 2 + H 2 Zinc + Hydrchlric Zinc Hydrgen acid chlride 4

5 2C Atmic Structure, Reactins and Cmpunds Relative reactivities f Ca, Mg, Zn, and Cu based n their reactins with water and acid Reactin with Water Place a sample f each metal Ca, Mg, Zn, and Cu in a test tube Add water t each test tube Nte what happens Result: Calcium reacts and prduces hydrgen gas Cnclusin: Calcium is the mst reactive f the fur metals Reactin with Dilute Hydrchlric Acid Place a sample f each metal Ca, Mg, Zn, and Cu in a test tube Add dilute hydrchlric acid t each test tube Nte what happens Result: Calcium reacts and prduces lts f hydrgen gas bubbles Magnesium prduces bubbles but nt as many as calcium Zinc prduces bubbles but nt as many as zinc Cpper prduces n bubbles Cnclusin: In rder f decreasing activity Ca, Mg, Zn and Cu (Equatins nt required) Hydrcarbns Hydrcarbns are cmpunds that are made f carbn and hydrgen nly Fssil fuels are ur main surces f hydrcarbns Made frm the fssilised remains f plants and animals millins f years ag Cal Crude il Natural gas which is mainly methane Peat (much mre recent 5 10,000 years ag) Nt made any mre as cnditins have changed Limited supply (nn-renewable) s they will run ut smetime Need t be cnserved They are used as fuels and t make plastics Many cntain traces f sulphur Cmbustin f Fssil Fuels Oil Well - Gusher We burn huge amunts f fssil fuels petrl, diesel, kersene (jet fuel) Hydrcarbn + Oxygen CO 2 + H 2 O + heat when burned CO 2 is a greenhuse gas and cntributes t glbal warming CO 2 disslves in rain t frm carbnic acid. This is nt acid rain (nrmal rain is slightly acidic) Acid Rain Cause The sulphur impurities in fssil fuels prduce SO 2 when they burn SO 2 disslves in rain t frm sulphuric acid and this is acid rain Effects Kills plants, Kills fish and ther aquatic life Reacts with limestne disslving it quickly and leading t crrsin f buildings Reacts with irn in cars and buildings causing crrsin Reduces the fertility f agricultural land Remedies Use lw sulfur fuels e.g. natural gas Acidified lakes can be imprved by adding lime (a base) which neutralises the acid Crrded Statue Dying Trees 5

6 2C Atmic Structure, Reactins and Cmpunds Plastics Substances that are made frm chemicals btained frm crude il Gd heat insulatrs Gd electrical insulatrs Waterprf Strng and flexible Lng lasting Resistant t chemical attack Everyday Applicatins f Plastics Plastic Use Prperties n which use depends Plythene Plastic bags, squeezy bttles, lunchbxes Flexible, strng, resistant t chemicals Rigid PVC Windw and dr frames, gutters, flr tiles Weather resistant, lng lasting Flexible PVC Electric wire insulatin, hsepipes Electrical insulatr, flexible, lng lasting Plystyrene Yghurt pts, fd cntainers Strng (but brittle), waterprf Expanded Plystyrene Shck prf packaging f delicate bjects, drink cups, insulatin in cavity walls Very gd heat insulatr, gd shck absrber Nyln Tights, shirts, carpets, cmbs Can be spun int fibres, dirt resistant Perspex Windws, light cvers in cars Tugh, rigid, transparent, light Plastics and Pllutin Substances which are nt brken dwn by bacteria, fungi and ther living rganisms are said t be nn-bidegradable They can last fr thusands f years and can thus cause pllutin e.g. plastic bags lk terrible in hedges, can chke and kill animals, etc Recycling reduces pllutin Tax n plastic bags has greatly reduced pllutin Rle f Chemistry Chemistry affects mst areas f ur daily lives Pharmacy Making perfumes and sap Making medicines Fuels Fd T keep us warm Drive ur vehicles Making packaging e.g. crisp packets Mdifying fd e.g. turning vegetable ils int margarine Agriculture Making fertilisers Making cleaning chemicals Building Industry Making cement and cncrete Making PVC windws, drs and gutters Husehld Appliances Making plastics fr kitchen utensils Televisin cases 6