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The Electronic Structure of Atoms Chapter 7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Properties of Waves ________________________ (l) is the distance between identical points on successive waves. _________________________ is the vertical distance from the midline of a wave to the peak or trough. ________________________ (n) is the number of waves that pass through a particular point in 1 second (Hz = 1 cycle/s). The speed (u) of the wave = _________________ 7.1 Maxwell (1873), proposed that visible light consists of ________________________. Electromagnetic radiation is the emission and transmission of energy in the form of electromagnetic waves. Speed of light (c) in vacuum = _____________________ All electromagnetic radiation l• n = c 7.1 A photon has a frequency of 6.0 x 104 Hz. Convert this frequency into wavelength (nm). Does this frequency fall in the visible region? lxn=c l = _______________________ l = _______________________ l = _______________________ l = _______________________ 7.1 Mystery #1, “Black Body Problem” Solved by Planck in 1900 Energy (light) is emitted or absorbed in discrete units (quantum). Mystery #2, “Photoelectric Effect” Solved by Einstein in 1905 Light has both: 1. wave nature 2. particle nature 7.1 When copper is bombarded with high-energy electrons, X rays are emitted. Calculate the energy (in joules) associated with the photons if the wavelength of the X rays is 0.154 nm. E=hxn n=c/l E=hxc/l E = __________________________________________ E = ______________________ 7.2 Line Emission Spectrum of Hydrogen Atoms Every element has a unique emission spectrum (p.200) 7.3 Bohr’s Model of the Atom (1913) 1. e- can have only specific (quantized) energy values 2. light is emitted as e- moves from one energy level to a lower energy level En = -RH ( 1 n2 ) n (principal quantum number) = 1,2,3,… RH (Rydberg constant) = 2.18 x 10-18J 7.3 Bohr showed the energy a H atom can have is equal to: En = -RH ( 1 n2 ) Ephoton = DE = Ef - Ei 1 Ef = -RH ( 2 nf 1 Ei = -RH ( 2 ni 1 DE = RH( 2 ni ) ) 1 n2f ) RH is the Rydberg constant pp.200-202 n is the principal quantum number 7.3 Calculate the wavelength (in nm) of a photon emitted by a hydrogen atom when its electron drops from the n = 5 state to the n = 3 state. Ephoton = DE = RH( 1 n2i 1 n2f ) Ephoton = 2.18 x 10-18 J x (1/25 - 1/9) Ephoton = DE = -1.55 x 10-19 J Ephoton = h x c / l l = h x c / Ephoton l = ________________________ 7.3 Why is e- energy quantized? De Broglie (1924) reasoned that e- is both particle and wave. 2pr = nl l = h/mu u = velocity of em = mass of ep.204 7.4 What is the de Broglie wavelength (in nm) associated with a 2.5 g Ping-Pong ball traveling at 15.6 m/s? l = h/mu h in J•s m in kg u in (m/s) l = ____________________________________ l = ____________________________________ 7.4 Schrödinger Wave Equation In 1926 _________________ wrote an equation that described both the particle and wave nature of the e____________________ (Y, psi) describes: 1. energy of e- with a given Y 2. probability of finding e- in a volume of space Schrödinger’s equation can be solved exactly only for ___________________________________. We must approximate its solution for multi-electron systems. 7.5 Schrödinger Wave Equation Y = fn(n, l, ml, ms) ______________________________ n n = 1, 2, 3, 4, …. n=3 n=2 n=1 distance of e- from the nucleus 7.6 Where 90% of the e- density is found for the 1s orbital e- density (1s orbital) falls off rapidly as distance from nucleus increases 7.6 Schrödinger Wave Equation Y = fn(n, l, ml, ms) ______________________________ l for a given value of n, l = 0, 1, 2, 3, … n-1 n = 1, l = 0 n = 2, l = 0 or 1 n = 3, l = 0, 1, or 2 l=0 l=1 l=2 l=3 s orbital p orbital d orbital f orbital Shape of the “volume” of space that the e- occupies 7.6 l = 0 (s orbitals) l = 1 (p orbitals) 7.6 l = 2 (d orbitals) 7.6 Schrödinger Wave Equation Y = fn(n, l, ml, ms) ______________________________ ml for a given value of l ml = -l, …., 0, …. +l if l = 1 (p orbital), ml = -1, 0, or 1 if l = 2 (d orbital), ml = -2, -1, 0, 1, or 2 orientation of the orbital in space 7.6 ml = -1 ml = -2 ml = 0 ml = -1 ml = 0 ml = 1 ml = 1 ml = 2 7.6 Schrödinger Wave Equation Y = fn(n, l, ml, ms) ______________________ ms ms = ______ or ______ ms = +½ ms = -½ 7.6 Schrödinger Wave Equation Y = fn(n, l, ml, ms) Existence (and energy) of an electron in an atom is described by its ______________ wave function Y. ________________________ — no two electrons in an atom can have the same four quantum numbers. Each seat in a stadium is uniquely identified (E, R12, S8) Each seat can hold only one individual at a time 7.6 Magnetic properties of atoms Paramagnetic atoms are attracted to a magnet. Any atom with an odd number of electrons is paramagnetic. Diamagnetic atoms are slightly repelled by a magnet. Atoms with an even number of electrons may be either paramagnetic or diamagnetic: •If there are unpaired electrons, it is paramagnetic •If there are no unpaired electrons, it is diamagnetic p.215 _____________________ unpaired electrons 2p ______________________ all electrons paired 2p 7.8 Schrödinger Wave Equation Y = fn(n, l, ml, ms) _______________ – electrons with the same value of n _________– electrons with the same values of n and l _______– electrons with the same values of n, l, and ml 7.6 Schrödinger Wave Equation Y = fn(n, l, ml, ms) How many electrons can an orbital hold? If n, l, and ml are fixed, then ms = ½ or - ½ Y = (n, l, ml, ½) or Y = (n, l, ml, -½) An orbital can hold _______ electrons 7.6 How many 2p orbitals are there in an atom? n=2 If l = 1, then ml = -1, 0, or +1 2p l=1 ___ orbitals 7.6 How many electrons can be placed in the 3d subshell? n=3 3d If l = 2, then ml = -2, -1, 0, +1, or +2 l=2 _____ orbitals which can hold a total of _____ e- 7.6 Energy of orbitals in a ____________ electron atom Energy depends only on principal quantum number n n=3 n=2 En = -RH ( 1 n2 ) n=1 7.7 Energy of orbitals in a ___________-electron atom Energy depends on n and l n=3 l = 2 n=3 l = 0 n=2 l = 0 n=3 l = 1 n=2 l = 1 n=1 l = 0 7.7 Fill lowest energy orbitals first (______________ principle) H 1 electron H 1s1 7.7 Fill lowest energy orbitals first (Aufbau principle) He 2 electrons He 1s2 7.7 Fill lowest energy orbitals first (Aufbau principle) Li 3 electrons Li 1s22s1 7.7 Fill lowest energy orbitals first (Aufbau principle) Be 4 electrons Be 1s22s2 7.7 Fill lowest energy orbitals first (Aufbau principle) B 5 electrons B 1s22s22p1 7.7 Fill lowest energy orbitals first (Aufbau principle) ? C 6 electrons C 1s22s22p2 7.7 ______________: The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins. C 6 electrons C 1s22s22p2 7.7 Hund’s rule: The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins. ? N 7 electrons N 1s22s22p3 7.7 Hund’s rule: The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins. N 7 electrons N 1s22s22p3 7.7 Hund’s rule: The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins. O 8 electrons O 1s22s22p4 7.7 Hund’s rule: The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins. F 9 electrons F 1s22s22p5 7.7 Hund’s rule: The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins. Ne 10 electrons Ne 1s22s22p6 7.7 Order of orbitals (filling) in multi-electron atom 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s 7.7 What is the electron configuration of Mg? Mg 12 electrons 1s < 2s < 2p < 3s < 3p < 4s ___________________ 2 + 2 + 6 + 2 = 12 electrons Abbreviated as [Ne]______ [Ne] is 1s22s22p6 7.7 What are the possible quantum numbers for the last (outermost) electron in Cl? Cl 17 electrons 1s < 2s < 2p < 3s < 3p < 4s ____________________ 2 + 2 + 6 + 2 + 5 = 17 electrons Last electron added to 3p orbital n=3 l=1 ml = -1, 0, or +1 ms = ½ or -½ 7.7 Outermost subshell being filled with electrons 7.8 ______________________ unpaired electrons 2p ______________________ all electrons paired 2p 7.8