Quantum Physics

28.9 The Exclusion Principle and the Periodic Table 919TABLE 28.4Electronic Configurations of Some ElementsGround-State Ionization Ground-State IonizationZ Symbol Configuration Energy (eV) Z Symbol Configuration Energy (eV)1 H 1s 1 13.595 19 K [Ar] 4s 1 4.3392 He 1s 2 24.581 20 Ca 4s 2 6.11121 Sc 3d4s 2 6.543 Li [He] 2s 1 5.390 22 Ti 3d 2 4s 2 6.834 Be 2s 2 9.320 23 V 3d 3 4s 2 6.745 B 2s 2 2p 1 8.296 24 Cr 3d 5 4s 1 6.766 C 2s 2 2p 2 11.256 25 Mn 3d 5 4s 2 7.4327 N 2s 2 2p 3 14.545 26 Fe 3d 6 4s 2 7.878 O 2s 2 2p 4 13.614 27 Co 3d 7 4s 2 7.869 F 2s 2 2p 5 17.418 28 Ni 3d 8 4s 2 7.63310 Ne 2s 2 2p 6 21.559 29 Cu 3d 10 4s 1 7.72430 Zn 3d 10 4s 2 9.39111 Na [Ne] 3s 1 5.138 31 Ga 3d 10 4s 2 4p 1 6.0012 Mg 3s 2 7.644 32 Ge 3d 10 4s 2 4p 2 7.8813 Al 3s 2 3p 1 5.984 33 As 3d 10 4s 2 4p 3 9.8114 Si 3s 2 3p 2 8.149 34 Se 3d 10 4s 2 4p 4 9.7515 P 3s 2 3p 3 10.484 35 Br 3d 10 4s 2 4p 5 11.8416 S 3s 2 3p 4 10.357 36 Kr 3d 10 4s 2 4p 6 13.99617 Cl 3s 2 3p 5 13.0118 Ar 3s 2 3p 6 15.755Note: The bracket notation is used as a shorthand method to avoid repetition in indicating inner-shell electrons. Thus, [He] represents 1s 2 , [Ne] represents 1s 2 2s 2 2p 6 ,[Ar] represents 1s 2 2s 2 2p 6 3s 2 3p 6 , and so on.metals have a single outer electron in an s subshell. This electron is shielded fromthe nucleus by all the electrons in the inner shells. Consequently, it’s only looselybound to the atom and can readily be accepted by other atoms that bind it moretightly to form molecules.The elements in the seventh column of the periodic table are called thehalogens and are also highly active chemically. All these elements are lacking oneelectron in a subshell, so they readily accept electrons from other atoms to formmolecules.Quick Quiz 28.4Krypton (atomic number 36) has how many electrons in its next to outer shell(n 3)?(a) 2 (b) 4 (c) 8 (d) 18Applying Physics 28.3The Periodic TableScanning from left to right across one row of theperiodic table, the effective size of the atoms firstdecreases and then increases. What would cause thisbehavior?Explanation Starting on the left side of the periodictable and moving toward the middle, the nuclearcharge is increasing. As a result, there is an increasingCoulomb attraction between the nucleus and theelectrons, and the electrons are pulled into an averageposition that is closer to the nucleus. From the middleof the row to the right side, the increasing number ofelectrons being placed in proximity to each otherresults in a mutual repulsion that increases theaverage distance from the nucleus and causes theatomic size to grow.