ElectronConfigs - ATOMIC ELECTRON CONFIGURATIONS AND PERIODICITY 1 2 3 Arrangement of Electrons in Atoms Electrons in atoms are arranged as

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Unformatted text preview: ATOMIC ELECTRON CONFIGURATIONS AND PERIODICITY 1 2 3 Arrangement of Electrons in Atoms Electrons in atoms are arranged as Arrangement of Electrons in Atoms Each orbital can be assigned no more than 2 electrons! This is tied to the existence of a 4th SHELLS (n) (n) SUBSHELLS (l) (l) ORBITALS (ml) (m electron electron spin quantum number, ms. quantum number, the 4 5 6 Electron Spin Quantum Number, ms Can be proved experimentally that electron Can be proved experimentally that electron has a spin. Two spin directions are given by has a spin. Two spin directions are given by mss where mss = +1/2 and -1/2. m where m = +1/2 and -1/2. where +1/2 Electron Spin Quantum Number QUANTUM QUANTUM NUMBERS NUMBERS n ---> shell n ---> shell 1, 2, 3, 4, ... 1, 2, 3, 4, ... 0, 1, 2, ... n -- 1 0, 1, 2, ... n 1 -l ... 0 ... +l -l ... 0 ... +l +1/2 and -1/2 +1/2 and -1/2 Diamagnetic :: NOT attracted to a magnetic Diamagnetic NOT attracted to a magnetic field field ll ---> subshell ---> subshell mll ---> orbital m ----> orbital --> mss ---> electron spin m ----> electron spin --> Paramagnetic :: substance is attracted to a Paramagnetic substance is attracted to a magnetic field. Substance has unpaired magnetic field. Substance has unpaired electrons. electrons. electrons. Page 1 7 8 9 Electrons in Atoms Electrons in Atoms Electrons in Atoms Electrons in Atoms When n = 3, then ll = 0, 1, 2 When n = 3, then = 0, 1, 2 3s orbital 2e3s orbital 2ethree 3p orbitals 6ethree 3p orbitals 6efive 3d orbitals 10effive 3d orbitals ive 10eTOTAL = 18eTOTAL = TOTAL 18e- Pauli Exclusion Principle No two electrons in the same atom can have the same set of 4 quantum numbers. That is, each electron has a unique address. When n = 1, then l = 0 this shell has a single orbital (1s) to which 2e- can be assigned. When n = 2, then l = 0, 1 2s orbital three 2p orbitals TOTAL = TOTAL 2e6e8e- 10 11 12 Electrons in Atoms Electrons in Atoms When n = 4, then l = 0, 1, 2, 3 4s orbital 2ethree 4p orbitals 6efive 4d orbitals 10efive seven 4f orbitals 14eTOTAL = 32eTOTAL And many more! And many more! Assigning Electrons to Atoms Assigning Electrons to Atoms •• Electrons generally assigned to orbitals of Electrons generally assigned to orbitals of successively higher energy. successively higher energy. •• For H atoms, E = -- C(1/n 22). E depends only For H atoms, E = C(1/n ). E depends only on n. on n. •• For many-electron atoms, energy depends For many-electron atoms, energy depends on both n and l. on both n and l. •• See Figure 8.6, page 342 and Screen 8. 5. See Figure 8.6, page 342 and Screen 8. 5. See Assigning Electrons to Subshells • In H atom all subshells of same n have same energy. • In many-electron atom: a) subshells increase in energy as value of n + l increases. b) for subshells of same n + l, subshell with lower n is lower in energy. Page 2 13 14 15 Effective Nuclear Charge Electron Filling Order Figure 8.7 The reason for difference in energy for 2s and 2p subshells, for example, is subshells, effective nuclear charge, Z*. Effective Nuclear Charge, Z* Effective Nuclear Charge, Z* • Z* is the nuclear charge experienced by the outermost electrons. See p. 344 and See Screen 8.6. • Explains why E(2s) < E(2p) • Z* increases across a period owing to incomplete shielding by inner electrons. • Estimate Z* by --> [ Z - (no. inner electrons) ] • Charge felt by 2s e- in Li Z* = 3 - 2 = 1 • Be Z* = 4 - 2 = 2 •B Z* = 5 - 2 = 3 and so on! 16 Writing Atomic Electron Writing Atomic Electron Configurations Configurations Two ways of Two ways of writing configs. writing configs. configs. One is called One is called the the SPECTROSCOPIC NOTATION for H, atomic number = 1 Writing Atomic Electron Writing Atomic Electron Configurations Configurations Two ways of Two ways of writing writing configs. Other configs. Other configs. is called the is called the orbital box orbital box notation. notation. ORBITAL BOX NOTATION for He, atomic number = 2 Arrows 2 depict electron spin 1s 17 18 spectroscopic spectroscopic notation. notation. 1s 1 no. of electrons value of l 1s value of n One electron has n = 1, l = 0, m l = 0, ms = + 1/2 0, 1/2 Other electron has n = 1, l = 0, m l = 0, ms = - 1/2 0, 1/2 See “Toolbox” for Electron Configuration tool. Page 3 19 20 21 Lithium Lithium Group 1A Atomic number = 3 1s22s1 ---> 3 total electrons ---> 3p 3p 3s 2p 2p 2s 1s 1s 2s 3s Beryllium Beryllium Group 2A Atomic number = 4 1s22s2 ---> 4 total ---> electrons 3s 2p 2s 1s Boron Boron Group 3A Atomic number = 5 1s2 2s2 2p1 ---> 2s 2p ---> 5 total electrons 3p 22 23 24 Carbon Carbon Group 4A Atomic number = 6 1s2 2s2 2p2 ---> 2s 2p ---> 6 total electrons 3p 3s 2p 2s 1s Nitrogen Nitrogen Group 5A Atomic number = 7 1s2 2s2 2p3 ---> 2s 2p ---> 7 total electrons 3s 2p 2s 1s 2s 1s 2p Oxygen Oxygen Group 6A Atomic number = 8 1s2 2s2 2p4 ---> 2s 2p ---> 8 total electrons 3p Here we see for the first time HUND’S RULE . When placing electrons in a set of orbitals having the same energy, we place them singly as long as possible. 3p 3s Page 4 25 26 27 Fluorine Fluorine Group 7A Atomic number = 9 1s2 2s2 2p5 ---> 2s 2p ---> 9 total electrons 3p 3s 2p 2s 1s 3s 2p 2s 1s Neon Neon Group 8A Atomic number = 10 1s2 2s2 2p6 ---> 2s 2p ---> 10 total electrons 3p Electron Configurations of p-Block Elements Note that we have reached the end of the 2nd period, and the 2nd shell is full! 28 29 30 Sodium Sodium Group 1A Atomic number = 11 1s2 2s2 2p6 3s1 or 2s 2p 3s or “neon core” + 3s 1 [Ne] 3s1 (uses rare gas notation) Ne] (uses Note that we have begun a new period. Aluminum Aluminum Group 3A Atomic number = 13 1s2 2s2 2p6 3s2 3p1 2s 2p 3s 3p [Ne] 3s2 3p1 Ne] 3p 3p Phosphorus Phosphorus Group 5A Atomic number = 15 1s2 2s2 2p6 3s2 3p3 2s 2p 3s 3p [Ne] 3s2 3p3 Ne] 3p 3s 2p 2s 1s All Group 1A elements have [core]ns 1 configurations. configurations. All Group 3A elements have [core] ns2 np1 np configurations where n is the period number. All Group 5A elements have [core ] ns 2 np3 np configurations where n is the period number. 3p 3s 2p 2s 1s Page 5 31 32 33 Calcium Calcium Group 2A Atomic number = 20 1s2 2s2 2p6 3s2 3p6 4s2 2s 2p 3s 3p 4s [Ar] 4s2 Ar] All Group 2A elements have [core]ns2 configurations where n configurations is the period number. Relationship of Electron Configuration and Region of the Periodic Table Transition Metals Transition Metals Table 8.4 Table 8.4 All 4th period elements have the configuration [argon] nsx (n - 1)dy (n 1)d and so are “d-block” elements. • • • • Gray = s block Orange = p block Green = d block Violet = f block Chromium Iron Copper Transition Element Configurations 34 35 Lanthanides and Actinides Lanthanides and Actinides All these elements have the configuration [core] nsx (n - 1)dy (n - 2)fz (n 1)d (n 2)f and so are “f-block” elements. Lanthanide Element Configurations 36 3d orbitals used for 3d orbitals used for Sc -- Zn (Table 8.4) Sc Zn (Table 8.4) Cerium [Xe] 6s2 5d1 4f1 Xe] 5d 4f Uranium [Rn] 7s 2 6d1 5f3 Rn] 6d 5f 4f orbitals used for 4f orbitals used for Ce -- Lu and 5f for Ce Lu and 5f for Th -- Lr (Table 8.2) Th Lr (Table 8.2) Page 6 Ion Configurations Ion Configurations To form cations from elements remove 1 or more e- from subshell of highest n [or highest (n + l)]. P [Ne] 3s2 3p3 - 3e- ---> P3+ [Ne] 3s2 3p0 [Ne] 3p 3eNe] 3p 37 Ion Configurations Ion Configurations To form cations from elements remove 1 or more e- from subshell of highest n [or highest (n + l)]. P [Ne] 3s2 3p3 - 3e- ---> P3+ [Ne] 3s2 3p0 [Ne] 3p 3eNe] 3p 3p 3s 2p 2s 1s 2s 1s 3s 2p 3p 38 39 Ion Configurations Ion Configurations For transition metals, remove ns electrons and then (n - 1) electrons. Fe [Ar] 4s2 3d6 [Ar] 3d loses 2 electrons ---> Fe 2+ [Ar] 4s0 3d6 Ar] 3d 40 41 42 Ion Configurations Ion Configurations For transition metals, remove ns electrons and then (n - 1) electrons. Ion Configurations Ion Configurations For transition metals, remove ns electrons and then (n - 1) electrons. Ion Configurations Ion Configurations How do we know the configurations of ions? Determine the magnetic properties of ions. magnetic Ions with UNPAIRED ELECTRONS are UNPAIRED are PARAMAGNETIC . Without unpaired electrons DIAMAGNETIC . DIAMAGNETIC Fe [Ar] 4s2 3d6 [Ar] 3d loses 2 electrons ---> Fe 2+ [Ar] 4s0 3d6 Ar] 3d Fe 4s 3d 4s Fe2+ 3d Fe [Ar] 4s2 3d6 [Ar] 3d loses 2 electrons ---> Fe 2+ [Ar] 4s0 3d6 Ar] 3d Fe 4s 3d 4s Fe2+ 3d Fe3+ 4s 3d Page 7 ...
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This note was uploaded on 01/11/2011 for the course ENGINEERIN MAE 107 taught by Professor Pozikrizdis during the Fall '08 term at San Diego.

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