UNIT 5: ATOMIC THEORY & THE PERIODIC TABLE CHEMISTRY 215, DUFFEY, CHAPTER 4 & SECTION 6.1

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1 UNIT 5: ATOMIC THEORY & THE PERIODIC TABLE CHEMISTRY 215, DUFFEY, CHAPTER 4 & SECTION 6.1 BIG IDEAS (we will tuch n small parts f Chp.5 as well) 4.1 Early Ideas Abut Matter 4.2 Defining the Atm 4.3 Hw Atms Differ 4.4 Unstable Nuclei & Radiactive Decay 6.1 Develpment f the Peridic Table EARLY IDEAS ABOUT MATTER Greek Philsphers (Reference: ) Many Greek Philsphers subscribed t DEMOCRITUS (& Leucippus) B.C. First t prpse Atms Matter was made up f Different kinds f atms have Believed that atms culd nt be Thugh nt crrect abut everything, the belief in the existence f was far ahead f it s time. Ideas were met with ARISTOTLE (& Plat) B.C. Criticized and rejected He did nt believe existed, s atms Because Aristtle was s influential, Demcritus atmic ideas were Aristtle believed in the Matter is made f Aristtle had such great influence that the existence f atms went unchallenged fr mre than 2000 years! DEVELOPMENT OF THE ATOMIC THEORY The first atmic thery came abut frm the cmbinatin f ideas frm three laws: 1. Scientist credited:

2 2. 3. Scientist credited: Scientist credited: Duffey, Chem 215, Unit 5 Ntes, p. 2 Jhn Daltn unified these cncepts int his, and develped the first called the JOHN DALTON Daltn revised ideas but did it based n Daltn s Atmic Thery (1803) (yu shuld knw the pints f his thery s be sure t cpy r study the table - Refer/Reference: ) Revisins t the Thery Daltn s Atmic Thery was a huge step, but It was revised and mdified t ur current Atmic Thery. Examples f things that were wrng: Defining the ATOM Atms are Prtns, Neutrns, Electrns Istpes atms can have different masses Atms are s small that a slid cpper penny cntains 2.9 x atms, which is almst 5 trillin times the wrld ppulatin!! Even thugh atms are small, we can use a t get images f them. (nantechnlgy) THE ELECTRON The Cathde Ray Tube Sir William CROOKES Discvered Nw knwn as This led t the inventin f televisin! Mass and Charge f the Electrn J.J. THOMSON Discvered the (1897) Disprved part f Determined the f electrns

3 (JJ Thmsn cntinued) Rbert MILLIKAN A unifrm psitively charged sphere with negative electrns scattered thrugh it. Determined the n an electrn Duffey, Chem 215, Unit 5 Ntes, p. 3 Thmsn s Plum Pudding Mdel Used Thmsn s RATIO t als determine the f an electrn THE NUCLEUS Ernest RUTHERFORD (1911) He expected t Actual Results: Rutherfrd s experiment led him t cnclude that an ATOM was: With mving in this regin He named the dense psitive regin the charged, almst all the He develped the frm his results. MORE SUBATOMIC PARTICLES Rutherfrd eventually cncluded that the psitive charge was cntained in Hwever, this did nt accunt fr all the in the nucleus. James CHADWICK Shwed that the nucleus als cntained a particle with but n Called the This brught abut the cncept f Particles fund in the nucleus ( and ) ATOMIC MODEL EVOLUTION Rutherfrd s mdel vilated the The negative electrns rbiting the psitive nucleus shuld int the and destry the atm. Niels BOHR Develped the cncept f t fix Rutherfrd s mdel. Mdel (Electrns rbiting the nucleus)

4 Duffey, Chem 215, Unit 5 Ntes, p. 4 MODERN ATOMIC MODEL Werner HEISENBERG Yu cannt knw the and the f an electrn at the same time. Nucleus Cntaining ( ) and ( ) Electrn Clud Accunts fr almst all the Mstly with ( ) in The Mdern Atmic Mdel Accunts fr almst all f the Subatmic Particles Summary Table (Refer/Reference: ) ATOMIC MODELS Evlutin f the atmic mdel (Heisenberg) MODERN ATOMIC MODEL Mre abut the electrn clud: in the electrn clud Specifically in the r electrn level Distributin f Electrns in the clud: 1 st Energy Level 2 nd Energy Level 3 rd Energy Level 4 th Energy Level - gets mre cmplex and we will cver it in mre detail when we talk abut electrn cnfiguratin.

5 MODERN ATOMIC THEORY Atms are, they are made f The three subatmic particles are: Mre recently the discver f quarks Quarks cme in flavrs : Duffey, Chem 215, Unit 5 Ntes, p. 5 Atms frm ne element t anther, but NOT by chemical reactins. (nly by nuclear reactins) Atms f the same element are, they share chemical prperties but can differ in. Istpes! HOW ATOMS DIFFER Imprtant Atmic Terms: ATOMIC MASS UNITS Atmic Number (Z) - Fund Als the number f in a Mass Number (A) - Fund Exact Atmic Mass f the mass number based n the mass f a prtn and neutrn in nn-runded versins. Fund Average Atmic Mass - Fund Atmic Mass Units ( ) are defined as This is an arbitrarily selected standard because the exact mass f a single atm in grams is t small t be practical. It is nearly (but nt exactly) equal t r (see table) Exact Atmic Mass - S it s a decimal instead f a whle number Refer: Average Atmic Mass A weighted average f all knwn : Based n the Each istpe s cntributin is calculated by: Then the is fund. Example: Carbn has three istpes, but C-14 des nt have a majr effect n the mass s we can ignre it fr calculatins. C-12 has a relative abundance f 98.89% and C-13 has an abundance f 1.11%. Calculate the Average Atmic Mass. C-12 s cntributin: (12.000) * (0.9889) = C-13 s cntributin: ( ) * (0.0111) = Sum the cntributins: = Or yu can slve it all at nce: ( * ) + ( * ) = Average Atmic Mass

6 Duffey, Chem 215, Unit 5 Ntes, p. 6 YOU TRY: Oxygen has three istpic frms, O-16 (mass = ), O-17 (mass = ), and O-18 (mass = ). The percent abundances are %, 0.037%, and 0.204% respectively. What is the average atmic mass f xygen? MOST COMMON ISOTOPE Runding the frm the CAN give the mst likely istpe t be the mst abundant istpic frm. (but it desn t always wrk!) Example 1: Flurine s average atmic mass is The mst abundant istpe is likely (which is crrect) Example 2: Brmine s average atmic mass is Yu wuld think the mst abundant istpe is Actually nly tw istpes exist, and Is actually the mst abundant at % HOW ATOMS DIFFER Infrmatin abut elements can be fund n Including and Sme peridic tables include additinal infrmatin like, categries (such as ), xidatin states,, etc ISOTOPES Atms with but different IONS Istpes f an atm have the same Istpe Ntatin: Each istpe is identified by Ex. Cu-63, Cu-65 Ex. istpes) (hydrgen Ptassium Istpes (ntatin examples) Ins differ in the number f and therefre are a., they carry Example: Deuterium (H-2) has That means with a +1 and a 1 charge, it s

7 Duffey, Chem 215, Unit 5 Ntes, p. 7 (In example cntinued) If it it s electrn it still has the same number f That means it is nw since it has the +1 but n lnger has an. Since ins are frmed by the transfer f : If electrns are the in that frms is Called a If electrns are the in that frms is Called an DEVELOPMENT OF THE PERIODIC TABLE Jhann DÖBEREINER (1817) Nticed similarities in the three elements The atmic mass f is abut halfway between and He gruped them int a Other : and Jhn NEWLANDS (1863) Nticed a repetitin f in the elements after every element when listed in rder f He called this the Listed the knwn elements int Dmitri MENDELEEV ( , research als in the 1860 s) Fund a cnnectin between and Arranged the elements in rder f Ex. (three elements) the existence AND prperties f His ideas were accepted much faster than new ideas in science typically are because elements were discvered that fit his predictins. Lthar MEYER ( ) Did wrk that was t the wrk f and arund the same time. He is generally nt given fr the ideas because Mendeleev did ntice a few elements that with the f their grup. He allwed fr in his listed rder f increasing because f this. Ex. Mendeleev s is the riginal and fficial peridic table

8 Duffey, Chem 215, Unit 5 Ntes, p. 8 THE MODERN PERIODIC TABLE Henry MOSELEY ( ) Used t discver the in the nucleus f each element Atmic Number - Predicted the discver f Rerdered the peridic table based n instead f atmic weight Mseley s wrk: Bmbarded metals with high speed electrns in a vacuum tube Recrded the radiatin prduced (depends n the kind f metal used) Ntice as the number f prtns (atmic number) increased the wavelength f x-ray gets shrter (in sme cases the difference between 2 knwn elements was twice the nrmal difference between elements in a rw) Based n that, Mseley predicted the discver f an t fill the gap. Peridic Law - ATOMIC NOTATION A-X-Z Ntatin A cmmn ntatin that is used t Frm it yu can determine the number f: Prtns - Elemental Neutrns - Electrns If n charge is shwn: If a charge IS shwn: UNSTABLE NUCLEI AND RADIOACTIVE DECAY Nuclear Reactins can change an int a A nuclear reactin is a reactin that invlves a in the atm s nucleus In the 1890s sme scientists nticed that sme substances This ccurs because They lse energy by thrugh radiactive decay This prcess cntinues until they reach a nn-radiactive element

9 Duffey, Chem 215, Unit 5 Ntes, p. 9 TYPES OF RADIATION Alpha radiatin Made f Helium nuclei: Ex. Beta Radiatin Made f An electrn (e-) with Ex. Gamma Radiatin Made f A high-energy particle with (0) Nuclear Stability The primary factr that determines if a material is radiactive is the Atms with t many r tw few are and emit α r β particles until stable.