ElectronConfig - Electron Configuration and Periodicity...

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Electron Configuration and Electron Configuration and Periodicity Periodicity Chapter 8
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2 Introduction Introduction In 1869 Mendeleev arranged the elements in order of atomic weights to obtain his periodic table. In 1898, Curie’s discovered element Ra in a mixture which was primarily a compound of barium separated from an ore of uranium. Radium gave a new atomic line spectrum different than barium We explain periodic table in terms of electronic structure of atoms.
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3 Topics of Discussion Topics of Discussion Electron Spin and Pauli Exclusion Principle Building Up Principle and Periodic Table Orbital Diagrams of Atoms; Hund’s Rule Periodicity of Elements Atomic Radius Ionization Energy Electron Affinity Brief Descriptions of the Main-Group Elements
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4 Electron Spin and Pauli Exclusion Principle Exclusion Principle Spin quantum number: m s = +1/2 , m s = -1/2 The Pauli Exclusion Principle: no two electrons in an atom can have the same four quantum numbers. An orbital can hold at most two electrons and then only if the electrons have opposite spins.
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5 Example Example What is the maximum number of electrons in s, p, d, f subshells? Subshell Number of orbitals Maximum # of electrons s(l=0) 1 2 p(l=1) 3 6 d(l=2) 5 10 f(l=3) 7 14 #e =2(2l + 1) #e =2(2l + 1)
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6 Building-up Principle Building-up Principle Ground State(g.s.) Electron configuration associated with the lowest energy level of the atom. Every atom has only one Ground State but infinite number of excited states. Building-up(Aufbau) Principle : Electron configurations of the ground states of atoms are obtained by filling the subshells of increasing energy with electrons.
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7 Example Example Write down the electron configuration for the ground state of 25 Mn. 25 Mn : 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 , 25 Mn : [Ar]4s 2 3d 5 Noble-gas core: an inner-shell configuration corresponding to one of the noble gases: ns 2 np 6 Pseudo-noble-gas core: noble gas configuration together with (n-1) d 10 Valence electron: an electron in an atom outside the noble-gas or pseudo-noble-gas configuration
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8 Hund’s Rule and Orbital Diagrams Hund’s Rule and Orbital Diagrams Hund’s rule: the lowest energy arrangements of electrons in a subshell is obtained by putting electrons into separate orbitals of the subshell with the same spin QN before pairing electrons
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9 Magnetic Properties of Atoms Magnetic Properties of Atoms An electron in an atom behaves like a magnet. Two electrons in the same orbital with opposite spins are called paired electrons. Such pairing leads to the cancellation of the electrons magnetic effects. Diamagnetic substances , all electrons are paired. They are not attracted to a magnet (very slightly repeled) Paramagnetic substances , contain unpaired electron(s).
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