1.3 Electron configurations

1.3 Electron - UNIVERSITY OF ALBERTA INTRODUCTORY UNIVERSITY CHEMISTRY I(CHEM 101 Electron Structure in Atoms II Electron Configuration and the

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1 UNIVERSITY OF ALBERTA INTRODUCTORY UNIVERSITY CHEMISTRY I (CHEM 101) Electron Structure in Atoms II Electron Configuration and the Periodic Table Electron Spin Quantum Number Quantum Mechanical calculations give three quantum numbers (n, l and m l ). Because electrons spin along an axis, there is yet another quantum number: the electron spin quantum number , m s , needs to be introduced. Such spinning of electrical charge generates its own magnetic field. Electron-spin quantum number (m s ) can have two possible values: +½ or ↑ ; -½ or ↓ Evidence: A beam of silver atoms split into two in the presence of a magnetic field indicating two types of electrons for the odd electron of the silver atom (silver has 47 electrons). Please refer to fig. 8-33, p 313 of your text Thus, it takes three quantum numbers to define an atomic orbital but we need four quantum numbers to identify an electron in an atom . Quantum numbers Symbol Permitted values Significance Principal Angular momentum Magnetic Spin n l m l m s 1, 2, 3… 0, 1,2,3 ….(n– 1) 0, ± 1, ± 2, ± 3, ( ± l ) +½, -½ Energy and size of orbital Orbital shape (s, p, d, f) Orientation of orbital Direction of electron spin
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2 Radial probability distributions of electrons Recall: Electron density of the orbital (s orbitals as shown below): Although electron density is highest near the nucleus, it does not mean the electron spends most of its time around the nucleus . Highest electron density of 1s orbital Highest radial probability distribution of electron in 1s orbital Fig 7.17 p292 Electron probability density plot against distance Radial probability plot against distance 1s orbital 2s orbital 3s orbital Fig 7.16 p288
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3 Ψ 2 expresses probability that the electron is at a particular point within the atom. The sum of Ψ 2 values within each spherical layer at a distance r from the nucleus is the radial probability distribution of the electrons. Several important features from the radial probability distribution curves: In the 1s orbital, electron is most probably found at about 5.3 x 10 -11 m from the nucleus which is consistent with the Bohr’s first radius (5.29 x 10 -11 m) Although electron density for orbitals is highest near the nucleus, its radial probability is almost zero. Although electron in the 2s orbital is further than electron in the 1s orbital, there is probability of finding 2s electron close to the nucleus. (penetration) Although electron in the 2p orbital is closer to the nucleus than that of the 2s, it does not penetrate near the nucleus. No penetration Penetration 5.3 x 10 -11 m
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4 Multi-electron atoms Consider the ionization energies for the following three atomic species: He He + ++ ++ He He + Ionization energy, x 10 -18 J He He + 3.94 8.72 He + > He Note that the IE of He + > 2 x 3.94 x 10 -18 J. Why is it harder to remove the 2
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This note was uploaded on 03/24/2011 for the course CHEM 103 taught by Professor Mar during the Spring '08 term at University of Alberta.

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1.3 Electron - UNIVERSITY OF ALBERTA INTRODUCTORY UNIVERSITY CHEMISTRY I(CHEM 101 Electron Structure in Atoms II Electron Configuration and the

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