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Opposites attract

Opposites attract. attract. repel. In a many-electron atom, each electron feels both the attraction to the protons in the nucleus and the repulsion from other electrons. Silberberg, M. 2010. Principles of General Chemistry. 2 nd ed. New York: McGraw-Hill. Effective nuclear charge.

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Opposites attract

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  1. Opposites attract

  2. attract

  3. repel

  4. In a many-electron atom, each electron feels both the attraction to the protons in the nucleus and the repulsion from other electrons Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  5. Effective nuclear charge

  6. In a many-electron atom, each electron feels both the attraction to the protons in the nucleus and the repulsion from other electrons • Force of attraction increases as nuclear charge (# of protons) increases • Force of attraction decreases as the electron goes farther from the nucleus Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  7. In effect, the charge felt by an electron is less than the full nuclear charge Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  8. In effect, the charge felt by an electron is less than the full nuclear charge • The effective nuclear charge (Zeff) is the nuclear charge that is actually felt by an electron • An electron is shielded from the full charge of the proton • greatly by the inner electrons • only slightly by the other electrons in the same principal quantum number (n) • not at all by outer electrons Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  9. The effective nuclear charge and electron configuration are key in understanding the periodic trends • Atomic radius • Ionic radius • neutral vs. charged • isoelectronic series • Ionization energy • one atom vs. another • same atom • Electron affinity Physical properties Chemical properties

  10. Atomic radius

  11. Atomic radius is ½ the distance between the two nuclei in two adjacent atoms Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  12. *Radii in pm Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  13. Decreasing atomic radius Left to right: decreasing atomic radius • Zeff dominates • number of protons increases • electrons are added to the same n, so shielding by inner electrons does not change while shielding by electrons belonging to the same n is poor Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill. Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  14. Top to bottom: increasing atomic radius • n dominates • going down the group, each member has one more level of inner electrons that shield the outer electrons very effectively Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill. Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  15. Ionic radius:Neutral vs. charged

  16. If the atom forms a cation, its radius decreases • same number of protons • less electrons • electron-electron repulsion is reduced • the electron cloud becomes smaller Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  17. If the atom forms an anion, its radius increases • same number of protons • more electrons • electron-electron repulsion is enhanced • the electron cloud becomes bigger Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  18. Ionic radius:Isoelectronic series

  19. Ions having the same electron configuration and same number of electrons are said to be isoelectronic Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  20. Left to right: decreasing ionic radius • same number of electrons • increasing number of protons • stronger attraction between the protons and the electrons

  21. Ionization energy:One atom vs. another

  22. Ionization energy (IE) is the minimum energy required to remove an electron from a gaseous atom • The higher the IE, the more difficult it is to remove the electron energy + X(g) X+(g) + e- Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  23. Brown, , E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. 8th ed. Phils: Pearson Education Asia Pte. Ltd.

  24. Increasing ionization energy Left to right: increasing ionization energy • Zeff dominates • number of protons increases • same n • stronger attraction between the protons and the electrons • harder to remove an electron Brown, , E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. Phils: Pearson Education Asia Pte. Ltd. Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  25. Top to bottom: decreasing ionization energy • n dominates • there are more electrons in between the protons and the outer electrons • weaker attraction • easier to remove an electron Decreasing ionization energy Brown, , E. LeMay, and B. Bursten. 2000. Chemistry: The Central Science. Phils: Pearson Education Asia Pte. Ltd. Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  26. Ionization energy:Same atom

  27. If more than one electron could be removed from the same atom, there will be different IE values X(g) X+(g) + e- IE1 X+(g) X2+(g) + e- IE2 X2+(g) X3+(g) + e- IE3 . . . . . . Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  28. Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  29. For the same atom, IE1 < IE2 <IE3 • same number of protons, less electrons • same nuclear charge, less electron-electron repulsion • greater attraction between the proton and the remaining electrons • harder to remove another electron Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  30. There is a dramatic increase in IE when an electron is removed from an atom/ion with a noble gas configuration • the noble gas configuration is stable • removing another electron from it will result in instability Chang, R. 2002. Chemistry 7th ed. Singapore: McGraw-Hill.

  31. Electron affinity

  32. Electron affinity (EA) is the energy change accompanying the addition of electrons to atoms or ions • The more negative the electron affinity, the greater the tendency to accept an electron • Note: different books may use different sign conventions X(g) + e- X-(g) energy gained (+) or released (-) *usually released Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  33. *Energies in kJ/mol Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  34. Increasing(?) electron affinity Left to right: increasing(?) electron affinity • Zeff dominates • size decreases • stronger attraction between the protons and the added electron Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  35. Top to bottom: no general trend except for Group 1A • For Group 1A, • the nucleus is farther away from an electron being added • weaker attraction between the protons and the added electron Decreasing electron affinity Silberberg, M. 2010. Principles of General Chemistry. 2nd ed. New York: McGraw-Hill.

  36. Factors other than Zeff and atomic size affect electron affinities, so trends are not as regular as those for the other properties

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