Chemistry 121 Lectures 6 & 7: The Mdern View f the Atm and Its Relatin t the Peridic Table Chapter 2 in McMurry, Ballantine, et. al. 7 th editin HW #2: 2.42, 2.44, 2.48, 2.50, 2.52, 2.58, 2.60, 2.62, 2.66, 2.68, 2.72, 2.82, 2.90, 2.96, 2.98 Learning Objectives: 1. Relate atmic number t the peridic table 2. Divide the peridic table int majr grups a. Metals, nn-metals, metallids b. Alkali metals, alkaline earth metals, transitin metals, grup 6(16) nn-metals, halgens, and nble gases 3. Learn the basic prperties f imprtant grups within the peridic table 4. Knw the 3 majr subatmic particles, their apprximate masses, and their charges 5. Define atmic number, mass number, and istpe 6. Describe the difference between mass number and atmic weight 7. Appreciate why the atmic number can be left ut when writing the symbl fr a particular istpe 8. Determine the number f neutrns in an element based n atmic number and mass number 9. Determine the element based n mass number and the number f neutrns 10. Determine the least r mst stable istpe based n atmic weight and mass number fr a series f istpes 11. Given relative abundance f cntributing istpes, determine atmic weight 12. Define the principal energy level fr the placement f electrns in an atm 13. Define the energy subshell and the electrn rbital in particular, knw hw many electrns may be placed in a given energy subshell and rbital 14. Define a nble gas cnfiguratin and the implicatins regarding the bnding behavir f the elements
15. Define valence electrns 16. Draw Lewis dt symbls fr imprtant elements 17. Define Lewis structures 18. Draw Lewis structures fr simple mlecular species 2.1: Atmic Thery The idea f the atm as the indivisible, fundamental unit f matter had been arund since the time f Demcritus, ca. 460 370 BC. Atm derives frm the Greek atms, meaning nt t cut Three Subatmic Particles The electrn Sir J.J. Thmpsn & Rbert Millikan By passing a current thrugh a variety f gases in a sealed tube, Thmsn is able t determine that an identical charged particle is lst regardless f the gas that it derived frm, and always has the same mass t charge rati
The prblem was t then determine the charge f the electrn, frm which mass culd be determined by the mass t charge rati. Rbert Millikan designs and painstakingly executes his nw famus il drp experiment, where he bserves il drplets in free fall t determine their mass after bmbarding the system with inizing radiatin. By then applying knwn electric field strength and measuring the change in rate f fall, Millikan shwed that each drplet had sme whle number multiple f a fundamental charge, crrespnding t the number f electrns the drplet picked up. Matter was knwn t be neutral verall. If this is the case, there had t be an ppsitely charged particle t balance charge The nucleus Ernest Rutherfrd The particle scattering experiment and the nuclear atm: Rutherfrd s students Marsden & Geiger sht particles at gld fil. Mst f the time they pass thrugh, but ccasinally they bunce straight back 1 An particle is a high energy He nucleus (He atm withut its electrns) 1 http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/rutsca3.html
The extrardinary scattering angles bserved were nt cnsistent with the raisin/plum pudding mdel that had been put frward by Thmpsn. If the plum pudding mdel were t hld, the scattering pattern wuld have t lk like the simulatin immediately belw (by Prfessr Ruth Chabay). Instead, the results are nicely visualized in the 2 nd simulatin, shwing the high scattering angles in red. The nly pssible explanatin cnsistent with culmbic frces is ur mdern view f the nuclear atm
Fr the gld atm in particular Fr a generalized atm
Prtns cnfined tgether in an extrardinarily small space an intrductin t the rle f the neutrn Given like charges repel and ppsite charges attract, it makes sense that electrns wuld be attracted t the nucleus and rbit arund it Hwever, it makes n sense that we culd pack all f ur psitive charge int an extremely small vlume, yet this is clearly demnstrated by the landmark experiments abve Enter the neutrn as nuclear glue : 12 C is the standard by which we establish mass. 13 C is a stable nnradiactive element, 14 C is a lw energy emitter with a t 1/2 f 5730 years, and 11 C is a very shrt-lived, man-made psitrn emitter used in PET scans. Ratinalize the difference in stability between the varius istpes:
Questin: Why is H + ften referred t as a prtn? Answer: Questin: Why is it unnecessary fr H t have a neutrn? Answer: KNOW THIS TABLE (with regard t clumn 4, apprximate t unit value) 2.2: Elements and Atmic Number Atmic Number The number f prtns in an atm If we assume charge neutrality, then we can als say the atmic number indicates the number f electrns; f curse, this des nt hld if we are cnsidering an inic species Catin defined: Anin Defined: Questin: Atmic number is never variable fr a given atm why? Answer:
Mass Number The mass number is the cmbinatin f prtns and neutrns fr a given istpe and as such gives the mass f that istpe, with enugh precisin fr mst purpses The mass number is variable between istpes f a given element, as different istpes will have differing numbers f neutrns Questin: Pb mass an atmic number f 82 and an atmic weight f 207.2. What is the relative mass cntributin f all f the electrns in Pb? Determining the Number f Neutrns frm Atmic Number and Mass Number Questin: What is the number f neutrns in 31 P? What is the number f neutrns in 32 P? Determining the Element frm Mass Number and the Number f Neutrns Questin: Which element has a mass number f 37 and 20 neutrns?
2.3: Istpes and Atmic Weight Questin: Why is it apprpriate t write the nuclear symbl fr Carbn-13 as 13 C, mitting the leading subscript? Questin: 13 C is a stable istpe, whereas 14 C is a lw energy emitter with a t 1/2 f 5730 years. Which f the 2 istpes wuld have the greatest cntributin t the bserved mass f a sample f carbn? Atmic weight defined Atmic weight is the bserved atmic mass based n all f the istpes making up a sample f atms. The Atmic weight f C = 12.01. What is the relative rati f 12 C t 13 C? 12X + 13(1-X) = 12.01 Questin: What is the bserved atmic weight f Cl if Cl is cmprised f 2 istpes, 35 Cl, abundance 75.53 %, and 37 Cl, abundance 24.47 % Atmic weight vs. atmic mass: yu say ptat, I say atmic mass Which is a mre accurate term, atmic weight vs. atmic mass? Which is mre practical, atmic weight r atmic mass?
2.4: The Peridic Table First published in 1869, Dmitri Mendeleev based the Peridic Table n increasing atmic mass (atmic number wuld nt be established until the wrk f Rutherfrd and clleagues 50 years later) and recurring physical and chemical prperties, an amazing feat cnsidering many elements remained t be discvered at that time Based n ur mdern understanding f the behavir f the elements there are errrs in Mendeleev s table abve. Hwever, the main grup elements are remarkably well rganized, particularly the lighter nes, wing t the similarity f prperties within a grup and their abundance n Earth s surface 2. This will be the apprach we take as well, primarily fcusing n the main grup elements, emphasizing thse within the first 4 perids 2 Fr yur amusement, n the last 2 pages I have included a cuple f interesting figures shwing hw elements distribute thrughut the slar system and n Earth
The structure f the mdern peridic table is based n atmic number lighter elements n tp, heavier nes ne the bttm The basic classificatin f the Peridic Table Metals, nn-metals, and metallids (semi-cnductrs) T find the separatin between the metals and the nn-metals, g t the staircase The elements t either side f the staircase except Al and P are the metallids Thse elements further t the right are nn-metals, thse further t the left are the metals. The exceptin is H, which is very much a nnmetal and bnds by sharing electrns
Cvalent vs. inic bnding: Main grup (r representative) elements vs. transitin elements: 2.5: Sme Characteristics f Different Grups Specially Named Grups Lcatin (grup n.) and behavir f alkali metals: Lcatin: Behavir: Lcatin (grup n.) and behavir f alkaline earth metals: Lcatin: Behavir: Lcatin (grup n.) and lack f behavir f nble gases: Lcatin: Behavir: Lcatin (grup n.) and behavir f halgens: Lcatin: Behavir: Lcatin (grup n.) and behavir f grup 16 nn-metals: Lcatin: Behavir:
2.6-2.8: Electrnic Cnfiguratin f Atms & the Structure f the Peridic Table Guitars and Light frm Stars: The Vibrating String Analgy fr the Quantized Atm and the Grund State vs. Excited State Hydrgen Atm A few key events leading t the quantizatin f electrn energies: 1885: Jhann Balmer discvers there are different clred lines assciated with the visible spectrum f hydrgen 1900: Max Planck puts frward quantum thery electrmagnetic radiatin r light frm a surce, such as a mlecule, must be quantized 1905: Albert Einstein demnstrates the quantizatin f light via the phtelectric effect 1913: Neils Bhr puts frward the Bhr planetary mdel fr hydrgen, where the electrn has discrete quantized - allwed energy states 1923: Luis de Brglie puts frward particle wave thery in which electrns pssess the prperties f waves 1925: Erwin Schrödinger puts frward his wave equatin that describes hw electrn matter waves vary with lcatin and time arund the nucleus. The allwed slutins t this quantized wave equatin are knwn as wave functins. 1926: Max Brn shws the square f the wave functin defines an rbital a regin f space where the prbability f finding an electrn is high
In rder t slve the Schrödinger wave equatin fr the energy distributin f electrns in given regins f space arund the nucleus, ne must slve a cmplex set f differential equatins (again, the allwed slutins t which are the wave functins essentially indicating the rbitals where electrns are likely t reside). The allwed slutins as summarized belw. The principal pints t keep in mind are The principal energy level relates t distance frm the nucleus, with level 1 clsest. The clser an electrn can get t the nucleus, the lwer its energy (by bringing psitive and negative charge tgether) There are energy sublevels within the principal energy levels. These sublevels crrespnd t rbitals the regins f space the electrns are likely t be fund. The relatinship between the principal energy level, the energy sublevels, and the number f assciated rbitals is shwn belw The principal energy level Defined: Where the principal energy levels are fund n the peridic table: The energy subshells Defined: Where the subshell energy levels are fund in the peridic table:
Orbitals within an energy subshell: Defined: Where the rbitals are fund in the peridic table: Bear in mind Orbitals are where we ultimately place electrns the principal energy level and the energy subshells allw us t determine the distributin f rbitals When we place electrns in an rbital, we are placing them in a particular regin f space relative t the nucleus; as such, they have a defined shape Any given rbital can hld 2 and nly 2 electrns, which must have ppsite spins
Summarizing the energy levels: the perid number gives the main energy levels (1,2,3 ). Every time yu g t the next level, yu get extra sublevels t place electrns in (1s, 2s & 2p, 3s & 3p & 3d). Each f these sublevels can hld 4 mre electrns than the ne preceding it, due t the additinal number f rbitals they cntain In keeping with the principal that systems seek their lwest energy state, rbitals are filled frm lwest energy t highest, and since the clser a negatively charged electrn is t the psitively charged nucleus the lwer its energy, electrns are placed frm clsest t furthest away in rder t match the number f electrns t prtns in the neutral atm Ntice that the energy level f any rbital within a given energy subshell is identical; since the lwest energy state is achieved when the [like charged] electrns can get away frm each ther, rbitals in a given subshell are filled ne at a time It is particularly imprtant t nte there is a large energy jump between the last available place in the p rbitals and the next higher s rbital this is the key t the stability f the nble gases (figure p. 6) Curiusly, there is an energy crssver between 3d and 4s that is maintained at higher levels (figure p. 6)
We nw have enugh infrmatin t mre fully interpret the peridic table, realizing the prblem is finding the lwest energy placement f each electrn, in rder t match the number f prtns in the nucleus as we read acrss and dwn the peridic table Questin: What is the electrnic cnfiguratin f Br? There is tremendus stability in cmpletely filling the first principal energy level r the p energy sublevels as may be seen by the repeating gap in the energy sublevels n page 6. This is the primary determinant f the behavir f the elements Simply put atms want a nble gas electrn cnfiguratin
S atms try t achieve a nble gas cnfiguratin ; let s lk at sme inic examples: NaCl MgCl 2 K 2 S CaO Valence Electrns: Thse electrns in the utermst principal energy level are referred t as valence electrns. Since the previusly added electrns are in filled shells, they d nt participate in the reactins f that element the valence electrns are where the actin is! As a result there is a specific way f representing atms particularly thse in the first 3 perids called the Lewis dt symbl 2.9: Electrn-Dt Symbls Simply include the valence electrns arund the symbl fr the atm, recgnizing electrns will stay away frm ne anther until they have t be paired, and there are 4 rbitals t place electrns, and each rbital can nly hld 2 electrns Let us nw cut t the chase and shw hw Lewis dt symbls allw us t build Lewis structures, which are elegantly simple ways f depicting and predicting stable mlecules Atms can achieve a nble gas electrnic cnfiguratin by sharing electrns the shared electrns cunt twards the nble gas electrnic cnfiguratin f each atm invlved in the bnd.
Use the Lewis structure t shw hw C & H cme tgether t frm methane, CH 4, such that each has a nble gas cnfiguratin Use the Lewis structure t shw hw 2C & 6H cme tgether t frm ethane, C 2 H 6, s each has a nble gas cnfiguratin Use the Lewis structure t shw hw 2C & 4H cme tgether t frm ethylene, C 2 H 4, s each has a nble gas cnfiguratin Use the Lewis structure t shw hw 2C & 2H cme tgether t frm acetylene, C 2 H 2, s each has a nble gas cnfiguratin Use the Lewis structure t shw hw O & H cme tgether t frm water, H 2 O, s each has a nble gas cnfiguratin
The distributin f elements amngst the planets is nt unifrm. Slar wind and heat drve the lighter elements further twards the uter reaches f the slar system, where they calesced int the frms we knw tday
Initially mlten, the elements n earth separated int fractins based primarily n density and melting pint