Ch_08a - Chapter 8 Electron Configurations, Atomic...

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1 Chapter 8 Electron Configurations, Atomic Properties, and the Periodic Table 2 Orbital Energy Levels for Hydrogen and Multielectron Atoms Multielectron atom: • Subshells of different principal shells can have nearly identical energies. 3d ~ 4s Energy 1 s 2 s 2 p 3 s 3 p 3 d 4 s (4 p , 4 d , 4 f ) Hydrogen atom 1 s 2 s 2 p 3 s 3 p 3 d 4 s 4 p A typical multielectron atom • The subshells of a principal shell are at different energy level. • The energy of each orbital gets lower.
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3 Orbital Energy Levels for Multielectron Atoms Subshell energy increases according to : ns < np < nd < nf • The difference results from electron-electron repulsion: Screening or Shielding by inner electrons +Z s electron is most penetrating; closer to the nucleus on average p electron is less penetrating… Net nuclear charge felt by an electron is called the effective nuclear charge ( Z eff ). Z eff felt by different subshell electrons decreases according to: ns > np > nd > nf 4 Electron Configuration : • distribution of electrons among the various orbitals in the atom. Orbitals within a subshell are at same energy level. ( degenerate ) Multielectron Atoms # of electrons = atomic number The orbital in which each e- resides
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5 Three Rules for Electron configuration (1) Electrons occupy orbitals of the lowest energy available. 1 s , 2 s , 2 p , 3 s , 3 p , 4 s , 3 d , 4 p , 5 s , 4 d , 5 p , 6 s , 4 f , 5 d , 6 p , 7 s , 5 f , 6 d , 7 p 1 s 2 s 2 p 3 s 3 p 3 d 4 s 4 p 4 d 4 f 5 s 5 p 5 d 5 f 6 s 6 p 6 d 7 s 7 p Increasing energy 6 (2) Pauli exclusion principle : no two electrons in the same atom may have all four quantum numbers alike. Atomic orbital: n , l , m l Only two values of m s : + ½ and - ½. An atomic orbital can accommodate only two electrons having opposing spins. n 12 3 4 n l 0 0 1 0 1 2 0 1 2 3 Subshell 1 s 2s 2p 3s 3p 3d 4s 4p 4d 4f Orbitals in 1 1 3 1 3 5 1 3 5 7 subshell Subshell capacity 2 2 6 2 6 10 2 6 10 14 Principal shell capacity 2 8 18 32 2 n 2
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7 (3) Hund’s rule : In orbitals of identical energy
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Ch_08a - Chapter 8 Electron Configurations, Atomic...

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