Electronic structure


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Electronic structure

  1. 1. ELECTRONIC STRUCTURE AND THE PERIODIC LAW Dr Sharipah Ruzaina Syed Aris srsa_july2009
  2. 2. <ul><li>The distribution of electrons among the orbitals of an atom is called the electronic structure or electronic configuration </li></ul>srsa_july2009
  3. 3. <ul><li>To indicate the ground state electron configuration we can: </li></ul><ul><ul><ul><li>List the subshells that contain electrons and indicate their electron population with a superscript. </li></ul></ul></ul><ul><ul><ul><li>Represent each orbital with a circle and use arrows to indicate the spin of each electron. </li></ul></ul></ul><ul><li>Electron configurations must be consistent with the Pauli principle, aufbau principle, and Hund’s rule </li></ul><ul><ul><ul><li>Example: N 1 s 2 2 s 2 2 p 3 , Na 1 s 2 2 s 2 2 p 6 3 s 1 </li></ul></ul></ul>srsa_july2009
  4. 4. <ul><li>Electron configurations explain the structure of the periodic table </li></ul>The periodic table is divided into regions of 2, 6, 10, and 14 columns which is the maximum number of electrons in s , p , d , and f sublevels. Subshells that fill across the periods. srsa_july2009
  5. 5. <ul><li>For the representative elements (A Groups) the electrons with the highest n value or valence shell are normally the only electrons important for chemical properties </li></ul><ul><li>For these elements the valence electrons consist of just the s and p subshells encountered crossing the period that contains the element in question </li></ul><ul><ul><ul><li>Example: the valence configuration of bromine is </li></ul></ul></ul><ul><ul><ul><li>Br 4 s 2 4 p 5 </li></ul></ul></ul>srsa_july2009
  6. 6. <ul><li>There are few important exceptions to the “expected” electronic figurations of commonly encountered elements </li></ul><ul><li>Following the rules for Cr, Cu, Ag, and Au using noble gas notation: </li></ul>srsa_july2009
  7. 7. Illustrating Orbital Occupancies The electron configuration n l # of electrons in the sublevel The orbital diagram (box or circle) Order for filling energy sublevels with electrons srsa_july2009 as s,p,d,f
  8. 8. dark - filled, spin-paired light - half-filled no color-empty A vertical orbital diagram for the Li ground state srsa_july2009
  9. 9. srsa_july2009
  10. 10. Condensed ground-state electron configurations in the first three periods. srsa_july2009
  11. 11. srsa_july2009
  12. 12. srsa_july2009
  13. 13. A periodic table of partial ground-state electron configurations srsa_july2009
  14. 14. PERIODIC TRENDS IN ATOMIC PROPERTIES *size *Ionization energy *electron affinity srsa_july2009
  15. 15. <ul><li>Variation in atomic and ionic radii. Values in picometers (10 -12 m) </li></ul>srsa_july2009
  16. 16. <ul><li>The size trends in ions can be summarized: </li></ul><ul><ul><li>Positive ions are always smaller than the atoms they are formed </li></ul></ul><ul><ul><li>Negative ions always larger than the atoms from which they are formed </li></ul></ul>Adding electrons leads to an increase in size of a particle, as illustrated for fluorine. Removing electrons decreases the size of the particle, as shown for lithium and iron. srsa_july2009
  17. 17. <ul><li>Ionization energy (IE) is the energy required to remove an electron from an isolated, gaseous atom </li></ul><ul><li>Successive ionizations are possible until no electrons remain </li></ul><ul><li>The trends in IE are the opposite of the trends in atomic size </li></ul>srsa_july2009
  18. 18. Periodicity of first ionization energy (IE 1 ) srsa_july2009
  19. 19. Variations in first ionization-energies. Elements with the largest ionization energies are in the upper right of the periodic table. Those with the smallest ionization energy are at the lower left. srsa_july2009
  20. 20. Ranking Elements by First Ionization Energy PLAN: SOLUTION: (a) Kr, He, Ar (b) Sb, Te, Sn (c) K, Ca, Rb (d) I, Xe, Cs IE decreases as you proceed down in a group; IE increases as you go across a period. Group 8A(18) - IE decreases down a group. Period 5 elements - IE increases across a period. Ca is to the right of K; Rb is below K. I is to the left of Xe; Cs is furtther to the left and down one period. srsa_july2009 PROBLEM: Using the periodic table only, rank the elements in each of the following sets in order of decreasing IE 1 : (a) He > Ar > Kr (b) Te > Sb > Sn (c) Ca > K > Rb (d) Xe > I > Cs
  21. 21. <ul><li>The electron affinity (EA) is the potential energy change associated with the addition of an electron to a gaseous atom or ion in its ground state </li></ul><ul><li>The addition of one electron to a neutral atom is exothermic for nearly all atoms </li></ul><ul><li>The addition of more electrons requires energy </li></ul>srsa_july2009
  22. 22. Electron affinities of the main-group elements. srsa_july2009
  23. 23. <ul><li>In general: </li></ul><ul><ul><li>EA increases from left to right in a period </li></ul></ul><ul><ul><li>EA increases bottom to top in a group </li></ul></ul>srsa_july2009
  24. 24. Trends in three atomic properties. srsa_july2009
  25. 25. <ul><li>Which has the larger second ionization energy? </li></ul><ul><li>lithium or beryllium </li></ul><ul><li>Why? </li></ul>srsa_july2009
  26. 26. <ul><li>Arrange the elements oxygen, fluorine, and sulfur according to increasing </li></ul><ul><ul><li>Ionization energy </li></ul></ul><ul><ul><li>Atomic size </li></ul></ul>srsa_july2009