AS OCR Chemistry 1.1 The Changing Atom

AS Level OCR Chemistry Revision:

Unit 1, Module 1: The Changing Atom.

HideShow resource information
Preview of AS OCR Chemistry 1.1 The Changing Atom

First 76 words of the document:

ASChemistry:Unit1AliceRosen12BP
Module1:AtomsandReactions
The Changing Atom
FifthcenturyBC­Democritus
Democritusdevelopedthefirstideaoftheatom.
Hebelievedanatomcouldnotbesplitanyfurther;thisiswhatyou
wouldendupwithifyoudividedasampleofmattersomanytimes.
Hecalledthisparticle`atamos'­Greekforindivisible.
Early1800s­JohnDalton
Daltonbelievedthatatomsaretinyparticles
thatmakeupelementsandareindivisible.
Hepredictedthatallatomsofagiven
elementarethesame.
Hepredictedthatatomsofoneelementare
differentfromthoseofeveryotherelement.
Daltonusedhisownsymbolstorepresent
atomsofdifferentelementsanddeveloped
thefirsttableofatomicmasses.
1897-1906­JosephJohnThomson
Thomsondiscoveredtheelectronthroughaseriesof
experimentsusingcathoderays.
Hewasabletoshowthatatomsweremadeupofsmallerparticles,
thusdisprovingtheideasproposedbytheancientGreeksandDalton.
Hediscoveredthatcathoderayswereastreamofelectronsand
concludedthattheymusthavecomefromwithintheatomsofthe
electrodesthemselves.
Thomsonproposedthatanatomshouldbethoughtofasbeingmade
upofnegativeelectronsmovingaroundina`sea'ofpositivecharge.
This`plum-pudding'modelisneutralwithnooverallcharge.

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

ASChemistry:Unit1AliceRosen12BP
Module1:AtomsandReactions
1909-1911­ErnestRutherford
Rutherfordandtwoofhisstudentscarriedoutanexperimentthat
ledtothedownfalloftheplum-puddingmodel.
Theydirectedalphaparticlestowardsasheetofverythingoldfoil
andmeasuredanydeflectionoftheparticles.
Asmallpercentageofparticlesweredeflectedsignificantly,
indicatingasmall,concentratedpositivecharge.
Heproposedthemodelofthenuclearatom:
o Thepositivechargeofanatomandmostofits
massareconcentratedinanucleus,atthecentre.
o Negativeelectronsorbitthisnucleus.
o Mostofanatom'svolumewouldbeinthespace
betweenthetinynucleusandtheorbitingelectrons.
o Theoverallpositiveandnegativechargesmustbalance.
In1918,Rutherforddiscoveredtheproton.
1913­NeilsBohr
TheDanishphysicistalteredRutherford'smodel
toallowelectronstofollowonlycertainpaths,
otherwise,electronswouldspiralintothenucleus.
Thiswastheplanetaryatom,inwhichelectrons
orbitedacentralnuclear`sun'in`shells'.
1926­ErwinSchrödinger
Schrödingersuggestedthatanelectronhaswavepropertiesinan
atomandintroducedtheideaofatomicorbitals.
1932­JamesChadwick
TheEnglishphysicistbombardedlightelementswithhigh-energy-
particles.Hefoundthatanewtypeofradiationwasemitted,much
morepenetratingthananythathadbeendetectedbefore.
Heshowedthatthisnewtypeofradiationwasmadeupofuncharged
particleswithapproximatelythesamemassasaproton,knownas
neutrons.…read more

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »