7.33 Careful spectral analysis shows that the familiar yellow light of sodium lamps (such as street lamps) is made up of photons of two wavelengths, 589.0 nm and 589.6 nm. What is the difference in energy (in joules) between the photons with these wavelengths? For 589.0 nm, E= 3.377 x 10-19 J For 589.6 nm, E= 3.373 x 10-19 J ΔE= (3.377x10-19)-(3.373x10-19)= 3.526x10-22 J 11/27/2018 S.A. McFarland©2006

6.57 From the standard enthalpies of formation, calculate ΔHorxn for the reaction C6H12(l) + 9O2(g) -> 6CO2(g) + 6H2O(l). For C6H12(l), ΔHof = -151.9 kJ/mol. -3924 kJ 11/27/2018 S.A. McFarland©2006

7.17 A photon has a frequency of 6.0x104 Hz. (a) Convert this frequency into wavelength (in nm). Does this frequency fall in the visible region? (b) Calculate the energy (in joules) of this photon. (c) Calculate the energy (in joules) of 1 mole of photons all with this frequency. 5x1012 nm, not in visible region 4.0x10-29 J 2.4x10-5 J/mol 11/27/2018 S.A. McFarland©2006

7.54 An electron in an atom is in the n=3 quantum level. List all of the possible values for l, ml, and ms that it can have. For n=3, l= 0,1, or 2. n=3, l=0, ml= 0, ms= +1/2 or -1/2 n=3, l=1, ml= -1, 0, 1, ms= =1/2 or -1/2 n=3, l=2, ml= -2, -1, 0, +1, +2, ms= =1/2 or -1/2 11/27/2018 S.A. McFarland©2006

“Fill up” electrons in lowest energy orbitals (Aufbau principle) ? ? Be 4 electrons Li 3 electrons B 5 electrons C 6 electrons B 1s22s22p1 Be 1s22s2 Li 1s22s1 He 2 electrons H 1 electron He 1s2 H 1s1 11/27/2018 S.A. McFarland©2006

The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins (Hund’s rule). N 7 electrons F 9 electrons Ne 10 electrons O 8 electrons C 6 electrons Ne 1s22s22p6 N 1s22s22p3 O 1s22s22p4 C 1s22s22p2 F 1s22s22p5 11/27/2018 S.A. McFarland©2006

Order of orbitals (filling) in multi-electron atom 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s 11/27/2018 S.A. McFarland©2006

Shielding effect in many-electron atoms Energy depends on n and l Compare 1s and 2s 1s lower in energy 1s is “stabilized” Harder to remove a 1s electron from the atom First filled are last removed 1s electrons are “happy” because they sit close to the nucleus (+) 2s electrons are “shielded” from the attractive force of nucleus by the 1s electrons 2s electrons easier to remove Compare 2s and 2p 2s has greater electron density near the nucleus 2s is shielded less by the 1s electrons (more penetrating) 2s electrons more strongly held by nucleus Penetrating power decreases as l increases (s > p > d > f > …) 2s lower in energy Harder to remove a 2s electron Easier to remove a 2p electron 11/27/2018 S.A. McFarland©2006

in the orbital or subshell Electron configuration is how the electrons are distributed among the various atomic orbitals in an atom. number of electrons in the orbital or subshell 1s1 principal quantum number n angular momentum quantum number l Orbital diagram 1s1 H 11/27/2018 S.A. McFarland©2006

Noble gas core The electronic configuration of all elements except H and He can be represented by a noble gas core, which abbreviates all core electrons as the nearest noble gas (noble gas that precedes the element of interest. For instance, Li: [He]2s1 11/27/2018 S.A. McFarland©2006

Core vs. valence electrons Li 1s22s1 [He]2s1 valence (outermost shell) core Valence electrons will determine chemical properties such as bonding and reactivity. 11/27/2018 S.A. McFarland©2006

What is the electron configuration of Mg? Mg 12 electrons 1s < 2s < 2p < 3s < 3p < 4s 1s22s22p63s2 2 + 2 + 6 + 2 = 12 electrons Abbreviated as [Ne]3s2 [Ne] = 1s22s22p6 What are the possible quantum numbers for the last (outermost) electron in Cl? Cl 17 electrons 1s < 2s < 2p < 3s < 3p < 4s 1s22s22p63s23p5 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 11/27/2018 S.A. McFarland©2006

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Exceptions Cr 1s22s22p63s23p64s23d4 [1s22s22p63s23p6]4s23d4 [Ar]4s23d4 There are several exceptions to the rules for assigning electrons to atomic orbitals. Learn these for Cu and Cr. Cr 1s22s22p63s23p64s23d4 [1s22s22p63s23p6]4s23d4 [Ar]4s23d4 [Ar]4s13d5 Cu also displays this irregularity Slightly greater stability is associated with the half-filled (3d5) and completely filled (3d10) subshells 11/27/2018 S.A. McFarland©2006

Outermost subshell being filled with electrons 11/27/2018 S.A. McFarland©2006

7.85 The electron configuration of a neutral atom is 1s22s22p63s2. Write a complete set of quantum numbers for each of the electrons. Name the element. 11/27/2018 S.A. McFarland©2006

7.104 Only a fraction of the electrical energy supplied to a tungsten lightbulb is converted to visible light. The rest of the energy shows up as infrared radiation (heat). A 75-W lightbulb converts 15.0% of the energy supplied to it into visible light (assume the wavelength to be 550 nm). How many photons are emitted by the lightbulb per second? (1 W = 1 J/s) 11/27/2018 S.A. McFarland©2006