Chapter 10 Modern Atomic Theory and the Periodic Table

10.1 A brief history10.1 A brief historyatoms proposed by Greek philosopherDalton’s model of atomThomson’s modelRutherford’s modelthere remain questions can not be answered:․ how atomic structure relates to the periodictable (arrangement of electrons)․ how to explain line spectrum of atom2

10.2 Electromagnetic radiationenergy and light – energy travels through space isby electromagnetic radiation,all radiations travel at the same speed –v = λ • υ = 3 × 10 -8 m/sλ : wavelengthυ : frequencyelectromagnetic spectrumwavelike nature -- radiationbehaves like particle -- photonexplain the properties of electromagneticradiation by both wave and particle properties3

10.3 The Bohr atomat high temperature or when subjected to highvoltage, elements in the gaseous state give offcolored lighta set of brightly colored lines – line spectrumex. line spectrum of hydrogenline spectrum indicates that light is being emittedonly at certain wavelength (or frequency)1912 Bohr model of hydrogen• electrons exit in specific regions at variousdistance from the nucleus• the electrons as revolving in orbits around thenucleus like planets rotating around the Sun4

Max Planck energy quantathe energy is never emitted in a continuousstream but only in small discrete packets calledquantaelectrons are only in several energy levelshydrogen atom absorbs one or more quanta ofenergy, the electron will jump to a higher energylevelground state– the lowest energy levelexcited states– the higher energy levelswhen an electron falls from a high-energy levelto a lower one, a quantum of energy is emittedas light at a specific frequencyBohr model1) suggesting quantized energy levels for electrons2) showing that spectral lines result from theradiation of small increments of energy whenelectrons shift from one energy level to anotherhowever, Bohr model only succeeded in H atom,5did not succeed for heavier atoms

1924 de Broglie all objects have wave propertiesfor small objects such as an electron, the waveproperties become significant1926 Schrödinger Schrödinger equationa mathematical model that described electronsas wavesthe probability of finding an electron in a certainregion around the atom can be determinedwave mechanics or quantum mechanicsforming the basis for our modern understandingof atomic structurewe cannot locate an electron precisely within anatomelectrons are not revolving around nucleus inorbits as Bohr postulatedorbital a region where a high probability offinding a given electron6

10.4 Energy levels of electronBohr the energy of the electron is quantizedthe electron is restricted to only certainallowed energieswave-mechanics also predicts discrete principalenergy levels within the atomthese energy levels aredesignated by the letter nn: positive integeras n increases, the energy of the electronincreases, and the electron is found on averagefarther from the nucleuseach principal energy levelis divided into sublevelsn = 1n = 2n = 31 sublevel2 sublevels3 sublevelseach of these sublevels contains space forelectrons called orbitals7

n = 1 1s orbital spherical shapethe electron does not move around on thesurface of sphere, the surface encloses a spacewhere there is a 90% probability that theelectron may be foundhow many electrons can fit into a 1s orbital?spin a property of electroneach electron can only spin in two directionsrepresentation of the spin ↑ or ↓two electrons with the same spin cannot occupythe same orbitalPauli exclusion principle – an atomic orbitalcan hold a maximum of two electrons whichmust have opposite spinsn = 1 energy level contains one type of orbital(1s) that hold a maximum of 2 electronsn = 2 2s spherical shapehold a maximum of two electrons2p – 2p x , 2p y , 2p z8

each p orbital has two lobes and can hold amaximum of two electronsthe total number of electrons that can reside inall three p orbitals is 6n = 3n = 2 energy level contains two types oforbitals (a 2s and three 2p) that hold amaximum of 8 electrons3s3p – 3p x , 3p y , 3p z3d – 3d xz , 3d xy , 3d yz , 3d z 2, 3d x 2 –y 2n = 3 energy level contains three types oforbitals (a 3s, three 3p, five 3d) that hold amaximum of 18 electrons9

valence electrons – the electrons un the outmost(highest) energy level of an atomex. O 1s 2 2s 2 2p 4 6 valence electrons12Mg 1s 2 2s 2 2p 6 3s 2 2 valence electrons

10.6 Electron structures and the periodictable1869 Mendeleev & Meyerperiodic arrangements of the elements based onincreasing atomic massesperiodic tableperiod – horizontal rowthe outmost energy levelgroup or family – vertical columnelements behave in a similar mannerIA ~ VIIA, IB ~ VIIB, VIII, noble gases1 ~ 18representative elements – A group elementstransition elements – B group elementsIA – alkali metals IIA – alkaline earth metals13VIIA – halogens

the valence electron configurations for H ~ Ar• the valence electron configuration for theelement in each column is the same, but thenumber for the energy level is different• the chemical behavior and properties of elementsin a particular family are similar and must beassociated with the electron configurationabbreviated electron configurationB 1s 2 2s 2 2p 1 [He] 2s 2 2p 1Cl 1s 2 2s 2 2p 6 3s 2 3p 5 [Ne] 3s 2 3p 5Na 1s 2 2s 2 2p 6 3s 1 [Ne] 3s 1n = 4 K 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 [Ar] 4s 1Ca 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 [Ar] 4s 2element 21 ~ 30 transition elementselectrons are placed in the 3d orbitals14

arrangement of elements according to thesublevel being filledinner transition elementslanthanide series –4factinide series –5fex. 10.1 write the electron configuration forP and SnP 1s 2 2s 2 2p 6 3s 2 3p 3 [Ne]3s 2 3p 3Sn 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 2[Kr] 5s 2 4d 10 5p 215

groups of elements show similar chemicalproperties because of the similarity of theseoutmost electron configurationsthe periodic table illustrates several importantpoints:1. the number of the period corresponds withthe highest energy level occupied byelectrons2. the group numbers for the representativeelements are equal to the total number ofoutmost electrons in the atom3. the elements of a family have the sameoutmost electron configuration, but indifferent energy level4. the elements within each of the s, p, d, fblocks are filling the s, p, d, f orbitals5. within the transition elements some 16discrepancies in the order of filling occur