Chapter 7 -lecture 2

Chapter 7 -lecture 2 - General Chemistry I Fall 2007 Joann...

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Unformatted text preview: General Chemistry I Fall 2007 Joann S. Monko Chemistry 9th ed. Raymond Chang The Electric Pickle Excited atoms can emit light. Soln' in pickle is excited electrically Light characteristic of Na+ ions Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Atomic Line Emission Spectra Niels Bohr Greatest contribution: built a simple model of the atom - based on understanding Niels Bohr SHARP LINE EMISSION SPECTRA of excited atoms. (1885-1962) Excited atoms emit light of only certain wavelengths. The wavelengths of emitted light depend on the element. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Spectrum of White Light Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Spectrum of Excited Hydrogen Gas Line Spectra of Other Elements High E Short High Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Low E Long Low Atomic Spectra and Bohr (early 20th century) atomic structure: an (e-) traveled about the nucleus in an orbit. 1. Any orbit should be possible & so is any energy. 2. But a charged particle moving in an electric field should emit energy. End result should be destruction! Bohr said classical view is wrong. New theory - The Bohr Model e- can only exist in certain discrete orbits - stationary states The e- is restricted to QUANTIZED energy states. Energy of state = - Rhc/n2 Kotz &Treichel where n = quantum no. = 1, 2, 3, 4, .... Chemistry & Chemical Reactivity 5th ed. Atomic Spectra and Bohr If e-'s are in quantized energy states, then E of states can have only certain values: Sharp Line Spectra Chang Chemistry, 8th ed. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Atomic Spectra and Bohr The potential energy of an e- in the nth level En = -Rhc Rhc = RH n2 R = Rydberg Constant = 1.097 x 107 m-1 H = Plank's Constant = 6.626 x 10-34 J s C = speed of light = 3.0 x 108 m/s E = Efinal Einitial E = Ef Ei = RH (1/n2initial - 1/n2final) where RH = 2.18 x 10-18 J Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Electron Transitions E=h E=h Chang Chemistry, 8th ed. Origin of Line Spectra Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Quantum or Wave Mechanics L. de Broglie (1892-1987) de Broglie (1924) proposed that all moving objects have wave properties. For light: E = mc2 = h = hc / Therefore, mc = h / and for particles (mass)(velocity) = h / Baseball (114 g) at 110 mph = 1.2 x 10-34 m e- with velocity = 1.9 x 108 cm/s = 0.388 nm Experimental proof of wave properties of electrons Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. E. Schrodinger 1887-1961 Schrodinger applied idea of e-'s behaving as a wave to the problem of e-'s in atoms. WAVE EQUATION Solution gives set of math expressions called WAVE FUNCTIONS, Each describes an allowed energy state of an eQuantization introduced naturally. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Wave Functions is a function of distance and two angles. Each corresponds to an ORBITAL -- the region of space within which an e- is found. does NOT describe the exact location of the e-. is proportional to the probability of finding an e- at a given point. 2 fn(n, l, ml, ms) n = 1, 2, 3, 4, .... n=1 n=2 n=3 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Chang Chemistry, 8th ed. Uncertainty Principle W. Heisenberg 1901-1976 Problem of defining nature of electrons in atoms solved by W. Heisenberg. Cannot simultaneously define the position and momentum (= mv) of an electron. We define e- energy exactly but accept limitation that we do not know exact position. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. s orbital p orbital d orbital No more than 2 e- assigned to an orbital Orbitals grouped in s, p, d (and f) subshells Orbitals s orbitals Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. p orbitals d orbitals s orbitals No. orbs. No. e- p orbitals d orbitals 1 2 3 6 5 10 Types of Atomic Orbitals Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Subshells & Shells Subshells grouped in shells. Each shell has a number called the PRINCIPAL QUANTUM NUMBER, n n is the number of the period or row of the periodic table where that shell begins. It tells of the size and energy of the shell Quantum Numbers n (major) l (angular) ---> ml (magnetic) Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. The shape, size, and energy of each orbital is a function of 3 quantum numbers: ---> shell (n = 1, 2,... E = -R(1/n2)) subshell (type or shape) ---> designates an orbital within a subshell (orientation) 1s Orbital 3s Orbital Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. p Orbitals When n = 2, then l = 0, 1 Therefore, in n = 2 shell there are 2 types of orbitals -- 2 subshells For l = 0 ml = 0 this is a s subshell For l = 1 ml = -1, 0, +1 this is a p subshell with 3 orbitals For l = 1, there is a PLANAR NODE thru the nucleus. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. p Orbitals The three p orbitals lie 90o apart in space Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 2px Orbital 3px Orbital Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. d Orbitals When n = 3, what are the values of l? l = 0, 1, 2 and so there are 3 subshells in the shell. For l = 0, ml = 0 ---> s subshell with single orbital For l = 1, ml = -1, 0, +1 ---> p subshell with 3 orbitals For l = 2, ml = -2, -1, 0, +1, +2 ---> Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. d subshell with 5 orbitals d Orbitals See Figure 7.16 s orbitals have no planar node (l = 0) and so are spherical. p orbitals have l = 1, and have 1 planar node, and so are dumbbell shaped. This means d orbitals (with l = 2) have 2 planar nodes Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 3dxy Orbital 3dxz Orbital Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 3dyz Orbital 3dx2- y2 Orbital Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 3dz Orbital 2 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. f Orbitals When n = 4, l = 0, 1, 2, 3 so there are 4 subshells in the shell. For l = 0, ml = 0 ---> s subshell with single orbital For l = 1, ml = -1, 0, +1 ---> p subshell with 3 orbitals For l = 2, ml = -2, -1, 0, +1, +2 ---> d subshell with 5 orbitals For l = 3, ml = -3, -2, -1, 0, +1, +2, +3 ---> f subshell with 7 orbitals Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Arrangement of Electrons in Atoms e-'s are arranged as Each orbital can contain no more than 2 e-'s! SHELLS (n) SUBSHELLS (l) The 4th quantum number: Electron Spin, ms Experimental proof: an electron has a spin. Two spin directions are given by ms where ms = +1/2 and 1/2. ORBITALS (ml) Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Electron Spin Quantum Number Diamagnetic: NOT attracted to a magnetic field Paramagnetic: substance is attracted to a magnetic field. Substance has unpaired e-'s. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Quantum Numbers n ---> shell l ---> subshell ml ---> orbital 1, 2, 3, 4, ... 0, 1, 2, ... n - 1 -l ... 0 ... +l ms ---> electron spin +1/2 and -1/2 Pauli Exclusion Principle No two electrons in the same atom can have the same set of 4 quantum numbers. Each electron has a unique address. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Clicker Question What are the Quantum Numbers for the 5th electron of boron? A. n = 1, l = 1, ml = -1, ms = +1/2 B. n = 2, l = 1, ml = +1, ms = +1/2 C. n = 2, l = 1, ml = -1, ms = +1/2 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Assigning Electrons to Subshells 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. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Electron Filling Order Writing Atomic Electron Configurations Two ways of writing configs. first: spdf notation for H, atomic number = 1 spdf notation 1s value of n 1 no. of electrons value of l Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Writing Atomic Electron Configurations Two ways of writing configs: Other is called the orbital box notation. ORBITAL BOX NOTATION for He, atomic number = 2 Arrows depict electron spin 1s 2 1s One electron has n = 1, l = 0, ml = 0, ms = + 1/2 Other electron has n = 1, l = 0, ml = 0, ms = - 1/2 Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Electron Configurations and the Periodic Table Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Lithium Group 1A Atomic # = 3 1s22s1 3 total e-'s 3p 3s 2p 2s 1s Beryllium Group 2A Atomic # = 4 1s22s2 4 total e-'s 3p 3s 2p 2s 1s Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Boron Group 3A Atomic # = 5 1s2 2s2 2p1 5 total e-'s 3p 3s 2p 2s 1s Carbon Group 4A Atomic # = 6 1s2 2s2 2p2 6 total e-'s 3p HUND'S RULE: most stable arrangement max. # of unpaired e-'s with same spin. 3s 2p 2s 1s Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Nitrogen Group 5A Atomic # = 7 1s2 2s2 2p3 7 total e-'s 3p 3s 2p 2s 1s Oxygen Group 6A Atomic # = 8 1s2 2s2 2p4 8 total e-'s 3p 3s 2p 2s Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. 1s Fluorine Group 7A Atomic # = 9 1s2 2s2 2p5 9 total e-'s 3p 3s 2p 2s 1s Neon Group 8A Atomic # = 10 1s2 2s2 2p6 10 total e-'s 3p 3s *End of the 2nd period 2p 2s 1s *The 2nd shell is full! Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. Sodium Group 1A Atomic # = 11 1s2 2s2 2p6 3s1 or neon core + 3s1 [Ne] 3s1 Rare Gas Notation All Group 1A elements have [core]ns1 configurations. Aluminum Group 3A Atomic # = 13 1s2 2s2 2p6 3s2 3p1 [Ne] 3s2 3p1 3p 3s 2p 2s 1s Kotz &Treichel Chemistry & Chemical Reactivity 5th ed. All Group 3A elements have [core ] ns2 np1 configurations where n is the period number. ...
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This note was uploaded on 04/08/2008 for the course CHEM 100 taught by Professor Monko during the Winter '08 term at Kutztown.

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