Edexcel GCSE Chemistry Atomic Structure Notes PDF

Edexcel​ ​GCSE​ ​Chemistry Topic​ ​1:Key​ ​concepts​ ​in​ ​chemistry Atomic​ ​Structure Notes www.pmt.education 1.1 Describe​ ​how​ ​the​ ​Dalton​ ​model​ ​of​ ​an​ ​atom​ ​has​ ​changed​ ​over​ ​time because​ ​of​ ​the​ ​disc...

Edexcel​ ​GCSE​ ​Chemistry Topic​ ​1:Key​ ​concepts​ ​in​ ​chemistry Atomic​ ​Structure Notes www.pmt.education 1.1 Describe​ ​how​ ​the​ ​Dalton​ ​model​ ​of​ ​an​ ​atom​ ​has​ ​changed​ ​over​ ​time because​ ​of​ ​the​ ​discovery​ ​of​ ​subatomic​ ​particles John​ ​Dalton​ ​(1803) : He​ ​published​ ​his​ ​own​ ​three-part​ ​atomic​ ​theory: 1. All​ ​substances​ ​are​ ​made​ ​of​ ​atoms.​ ​Atoms​ ​are​ ​small​ ​particles​ ​that​ ​cannot be​ ​created,​ ​divided,​ ​or​ ​destroyed.​ ​ 2. Atoms​ ​of​ ​the​ ​same​ ​element​ ​are​ ​exactly​ ​alike,​ ​and​ ​atoms​ ​of​ ​different elements​ ​are​ ​different.​ ​ 3. Atoms​ ​join​ ​with​ ​other​ ​atoms​ ​to​ ​make​ ​new​ ​substances.​ ​ Much​ ​of​ ​Dalton’s​ ​theory​ ​was​ ​correct,​ ​but​ ​some​ ​of​ ​it​ ​was​ ​later​ ​proven​ ​incorrect and​ ​revised​ ​as​ ​scientists​ ​learned​ ​more​ ​about​ ​atoms. J.J.​ ​Thomson​ ​(1897) : Used​ ​a​ ​cathode-ray​ ​tube​ ​to​ ​conduct​ ​an​ ​experiment This​ ​discovery​ ​identified​ ​an​ ​error​ ​in​ ​Dalton’s​ ​atomic​ ​theory.​ ​Atoms​ ​can​ ​be divided​ ​into​ ​smaller​ ​parts. Because​ ​the​ ​beam​ ​moved​ ​away​ ​from​ ​the​ ​negatively​ ​charged​ ​plate​ ​and​ ​toward the​ ​positively​ ​charged​ ​plate,​ ​Thomson​ ​knew​ ​that​ ​the​ ​particles​ ​must​ ​have​ ​a negative​ ​charge. Thomson​ ​proposed​ ​a​ ​model​ ​of​ ​an​ ​atom​ ​called​ ​the​ ​“plum-pudding”​ ​model,​ ​in which​ ​negative​ ​electrons​ ​are​ ​scattered​ ​throughout​ ​soft​ ​blobs​ ​of​ ​positively charged​ ​material. Ernest​ ​Rutherford​ ​(1909) : Shot​ ​a​ ​beam​ ​of​ ​positively​ ​charged​ ​particles​ ​into​ ​a​ ​sheet​ ​of​ ​gold​ ​foil. Most​ o ​ f​ ​the​ ​particles​ ​did​ ​continue​ ​in​ ​a​ ​straight​ ​line​ ​(as​ ​you​ ​would​ ​expect​ ​from plum​ ​pudding​ ​model).​ ​However​ ​some​ ​of​ ​the​ ​particles​ ​were​ ​deflected​ ​to​ ​the​ ​sides a​ ​bit,​ ​and​ ​a​ ​few​ ​bounced​ ​straight​ ​back. Rutherford​ ​developed​ ​a​ ​new​ ​model​ ​which​ ​said​ ​that​ ​most​ ​of​ ​the​ ​atom’s​ ​mass​ ​is found​ ​in​ ​a​ ​region​ ​in​ ​the​ ​center​ ​called​ ​the​ ​nucleus. In​ ​Rutherford’s​ ​model​ ​the​ ​atom​ ​is​ ​mostly​ ​empty​ ​space,​ ​and​ ​the​ ​electrons​ ​travel in​ ​random​ ​paths​ ​around​ ​the​ ​nucleus. 1.2 Describe​ ​the​ ​structure​ ​of​ ​an​ ​atom​ ​as​ ​a​ ​nucleus​ ​containing​ ​protons and​ ​neutrons,​ ​surrounded​ ​by​ ​electrons​ ​in​ ​shells www.pmt.education 1.3 Recall​ ​the​ ​relative​ ​charge​ ​and​ ​relative​ ​mass​ ​of​ ​protons,​ ​neutrons​ ​and electrons particle relative​ ​charge relative​ ​mass proton +1 1 neutron 0 1 electron -1 1/1836 1.4 Explain​ ​why​ ​atoms​ ​contain​ ​equal​ ​number​ ​of​ ​protons​ ​and​ ​electrons Atoms​ ​are​ ​neutral​ ​and​ ​the​ ​charges​ ​on​ ​a​ ​proton​ ​are​ ​+1​ ​and​ ​on​ ​an​ ​electron​ ​are​ ​-1 therefore​ ​amount​ ​of​ ​protons​ ​=​ ​amount​ ​of​ ​electrons,​ ​so​ ​that​ ​the​ ​charges​ ​cancel 1.5 Describe​ ​the​ ​nucleus​ ​of​ ​an​ ​atom​ ​as​ ​a​ ​very​ ​small​ ​compared​ ​to​ ​the overall​ ​size​ ​of​ ​the​ ​atom 1.6 Recall​ ​that​ ​most​ ​of​ ​the​ ​mass​ ​of​ ​an​ ​atom​ ​is​ ​concentrated​ ​in​ ​the nucleus 1.7 Recall​ ​the​ ​meaning​ ​of​ ​the​ ​term​ ​mass​ ​number​ ​of​ ​an​ ​atom Mass​ ​(nucleon)​ ​Number​ ​=​ ​number​ ​of​ ​protons​ ​+​ ​neutrons 1.8 Describe​ ​atoms​ ​of​ ​a​ ​given​ ​element​ ​as​ ​having​ ​the​ ​same​ ​number​ ​of protons​ ​in​ ​the​ ​nucleus​ ​and​ ​that​ ​this​ ​number​ ​is​ ​unique​ ​to​ ​that​ ​element 1.9 Describe​ ​isotopes​ ​as​ ​different​ ​atoms​ ​of​ ​the​ ​same​ ​element​ ​containing the​ ​same​ ​number​ ​of​ ​protons​ ​but​ ​different​ ​numbers​ ​of​ ​neutrons​ ​in their​ ​nuclei 1.10 Calculate​ ​the​ ​numbers​ ​of​ ​protons,​ ​neutrons​ ​and​ ​electrons​ ​in​ ​atoms given​ ​the​ ​atomic​ ​number​ ​and​ ​mass​ ​number Atomic​ ​(proton)​ ​Number​ ​=​ ​number​ ​of​ ​protons​ ​(=​ ​number​ ​of​ ​electrons​ ​if​ ​it’s​ ​an atom,​ ​because​ ​atoms​ ​are​ ​neutral) therefore,​ ​you​ ​can​ ​calculate​ ​number​ ​of​ ​neutrons​ ​by​ ​doing​ ​mass​ ​number​ ​§ atomic​ ​number 1.11 Explain​ ​how​ ​the​ ​existence​ ​of​ ​isotopes​ ​results​ ​in​ ​relative​ ​atomic masses​ ​of​ ​some​ ​elements​ ​not​ ​being​ ​whole​ ​numbers because​ ​isotopes​ ​have​ ​the​ ​same​ ​number​ ​of​ ​protons​ ​but​ ​different​ ​numbers​ o ​ f neutrons,​ ​they​ ​are​ ​still​ ​atoms​ ​of​ ​the​ ​same​ ​element,​ ​but​ ​they​ ​have​ ​different atomic​ ​masses the​ ​relative​ ​atomic​ ​mass​ ​is​ ​calculated​ ​using​ ​the​ ​abundance​ ​of​ ​different​ ​isotopes and​ ​because​ ​it​ ​is​ ​an​ ​average​ ​it​ ​can​ ​lead​ ​to​ ​the​ ​relative​ ​atomic​ ​mass​ ​not​ ​being​ a​ whole​ ​number​ ​(atomic​ ​number​ ​and​ ​mass​ ​number​ ​will​ ​always​ ​be​ ​whole​ ​numbers- they​ ​are​ ​not​ ​averages) since​ ​the​ ​mass​ ​of​ ​atoms​ ​is​ ​so​ ​small,​ ​we​ ​compare​ ​their​ ​masses​ ​to​ ​each​ ​other.​ ​A carbon​ ​atom​ ​having​ ​a​ ​mass​ ​number​ ​12,​ ​i.e.​ ​(​12​C)​ ​is​ ​taken​ ​as​ ​standard​ ​for​ t​ his comparison​ ​and​ ​its​ ​relative​ ​atomic​ ​mass​ ​is​ ​12. It​ ​is​ ​written​ ​as​ ​Ar​ ​ ​or​ ​R.A.M.​. 1.12 (higher​ ​tier)​ ​Calculate​ ​the​ ​relative​ ​atomic​ ​mass​ ​of​ ​an​ ​element​ ​from the​ ​relative​ ​masses​ ​and​ ​abundances​ ​of​ ​its​ ​isotopes A​ ​sample​ ​of​ ​chlorine​ ​gas​ ​is​ ​a​ ​mixture​ ​of​ ​2​ ​isotopes, chlorine-35​ ​and​ ​chlorine-37.​ ​These​ ​isotopes​ ​occur​ ​in specific​ ​proportions​ ​in​ ​the​ ​sample​ ​i.e.​ ​75%​ ​chlorine-35 and​ ​25%​ ​chlorine-37.​ ​Calculate​ ​the​ ​R.A.M.​ ​of​ ​chlorine​ ​in the​ ​sample. The​ ​average​ ​mass,​ ​or​ ​R.A.M.​ ​of​ ​chlorine​ ​can​ ​be​ ​calculated using​ ​the​ ​following​ ​equation: ​ ​ ​(mass​ ​of​ ​isotope-A ​ ​x ​ ​%​ ​of​ ​isotope-A)​ ​+​ ​(mass​ ​of​ ​isotope-B​ ​ x ​ ​%​ ​of​ ​isotope-B) R.A.M. = ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​100 (35​ ​x​ ​75)​ ​+​ ​(37​ ​x​ ​25) ​ ​ ​= ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​100 3550 = 100 R.A.M. = 35.5 www.pmt.education