Chapter 8 Lecture Notes

Al e al ea 44 kjmol still small but positive si e si

This preview shows page 8 - 10 out of 10 pages.

Al + e → Al EA = +44 kJ/mol still small but positive Si + e → Si EA = +134 kJ/mol P + e → P EA = +72 kJ/mol S + e → S EA = +200 kJ/mol Cl + e → Cl EA = + 349 kJ/mol Ar + e → Ar EA <0, we cannot add an electron to the filled shells of Ar Note that for Mg to Al to Si the EA increases, but then we have EA(P)<EA(Si). This is because the half-filled p-shell of P is favourable, and an added electron would have to go in with antiparallel spin. Then again EA(P)<EA(S)<EA(Cl), but Ar with its filled s 2 p 6 configuration cannot accept another electron at all. The trend from top to bottom within a group also has no regularity, as you can see from the alkali metals and the halogens. Electron Affinities are quantities mainly of theoretical interest. While Ionization Energies can be determined from spectroscopic measurements, EA values are calculated indirectly, and in some cases can be found only from theoretical calculations. Still, EA values will 8
Image of page 8

Subscribe to view the full document.

be important to us, and to chemistry, when we combine EA and IE values in a new quantity called the electronegativity (EN), which we will encounter in Chapter 9. Don’t confuse Electron Affinity and Electronegativity! Example . 1. Of the following pairs of atoms, predict which atom wil have the highest EA value. a) Li and Be b) F and O c) F and Ne d) C and N e) Be and B Answer . a) Li, because Be has a s 2 configuration; b) F, because it is "to the right” of O; c) F, because Ne will not have a positive EA d) C (!) because adding an electron to N’s p 3 with three parallel spins, where the added electron would have to be antiparallel, is unfavourable e) B, because Be will have a very low or zero EA, just like Mg. Exercises 1. Write the electron configuration of a) Ca 2+ b) F c) Sc 3+ d) Mn 2+ e) Cu 2+ f) Sn 4+ , g) Pb 2+ h) S 2− i) I 2. For each of the following pairs, which atom or ion has the largest radius? a) Na and Mg b) K and Rb c) S and Cl d) F and Ne e) C and N f) Na and Na + g) F and F h) K + and Ca 2+ i) S 2− and Cl 3. For each of the following pairs, which atom has the highest 1 st IE value? a) Na and K b) Na and Mg c) C and N d) N and O e) O and F f) Na and Na + 4. Explain in words why the IE of N is higher than the IE of O 5. Explain in words why the Electron Affinity (EA) of Mg is lower than the EA of Na Additional problems in Chang: Chapter 8: problems 8.22, 8.24, 8.26, 8.32, 8.38, 8.44, 8.52, 8.62, 8.64 9
Image of page 9
Image of page 10

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern