Key to CHEM 411/512 Test 1 Spring 2008 (Delaney)



  1. Using the diatomic molecular orbital scheme above, tell the bond order of the diastmic species below and whther they are diamagnetic or paramagnetic. (10 points)

    1. NO+, B.O. = 3, diamagnetic

    2. BC, B.O. = 1.5, paramagnetic

    3. CF2-, B.O. = 1.5, paramagnetic

    4. Li2, B.O. = 1, diamagnetic

    5. C2, B.O. = 2, paramagentic

  2. Provide the electron configuaration for the elements below, following the Aufbau or building up principle. (10 points)

    1. V = [Ar]4s23d3

    2. Br = [Ar]4s23d104p5

    3. Ba = [Xe]6s2

    4. Nd = [Xe]6s24f4

    5. Te = [Kr]5s24d105p4

  3. Rationalize your way to the proper electron configuration for the exceptions to the Aufbau or building up principle shown below. (10 points)

    1. Cr = [Ar]4s13d5

    2. Ag = [Kr]5s14s10

    3. Gd = [Xe]6s24f75d1

    4. Pd = [Kr]5s04d10

    5. Au = [Xe]6s14f145d10

  4. What are the quantum numbers for the last electron placed for each of the elements in problems 2 and 3 (For electron configurations where an electron is promoted, use the quantum numbers of the orbital to which the electron is promoted.) ? (10 points)

    1. V, n = 3, l = 2, ml = 0, ms= +1/2

    2. Br, n=4, l=1, ml=0, ms= -1/2

    3. Ba, n=6, l=0, ml=0, ms= -1/2

    4. Nd, n = 4, l = 3, ml = 0, ms= +1/2

    5. Te, n = 5, l = 1, ml = -1, ms= -1/2

    6. Cr, n = 3, l = 2, ml = 2, ms= +1/2

    7. Ag, n = 4, l = 2, ml = 2, ms= -1/2

    8. Gd, n = 5, l = 2, ml = -2, ms= +1/2

    9. Pd, n = 4, l = 2, ml = 2, ms= -1/2

    10. Au, n = 5, l = 2, ml = 2, ms= -1/2

  5. Using the electronegativity chart printed on the back of the periodice table appended to the front of this test, tell whether the bonds between the atoms below would be classified as i) non-polar covalent, ii) polar covalent, or iii) ionic using Pauling's rule. (10 points)

      Pauling' rules: Difference of 0, non-polar covalent bond; Difference between 0 and 1.7, polar covalent bond; Difference greater than 1.7, ionic bond

    1. Al-C, 2.55 - 1.61 = 0.94, polar covalent bond

    2. H-H, 2.20 - 2.20 = 0, non-polar covalent bond

    3. Hg-H, 2.20 - 2.00 = 0.20, very slightly polar covalent bond

    4. Sc-Cl, 3.16 - 1.36 = 1.8, ionic bond

    5. K-Cl, 3.16 - 0.82 = 2.34, ionic bond

  6. Define or explain (in complete sentences, please!) (10 points)

    1. orbital - A three dimensional area of space within which there is a finite possibility of finding the electron.

    2. first ionization energy - the energy necessary to remove the outermost electron of an atom. It is usually expressed in kJ/mol.

    3. electron affinity - the enrgy released when an atom captures an electron to become an anion. It is usually expressed in kJ/mol.

    4. isoelectronic - A word meaning "having the same electron configuration."

    5. quantum number - A number expressing a certain allowed energy state.

    6. Heisenberg uncertainty principle - The Heisenberg uncertainty principle states that you cannot know the momentum and the position of a subatomic particle such as the electron to within a certain amount, designated by the equation:

      ΔxΔp = h/2π

    7. deBroglie relationship - A relationship which relates the momentum of particles of matter to a wavelength. This introduced the idea that matter has wave-like properties. The relationship is λ = h/mv .

    8. photon - A single quantum of light (first proposed by Einstein who postulated particle-like properties for light, by proposing that its energy was packaged in quanta he called photons).

    9. period - A period is a horizontal row on the periodic table.

    10. group or family - A group or family is a vertical column on the periodic table.

  7. For each of the compounds below i) draw a correct Lewis dot structure, ii) indicate the hybrid orbitals used by the central aton, iii) draw the structure (using VSEPR theory as your guide), and finally iv) provide the correct molecular structure name. (20 points)

    1. SeF4



    2. BeF2



    3. PBr3



    4. IF5



    5. BCl3



  8. Circle the larger of the species below: (10 points)

    1. Li or K

    2. P3- or V5+


    3. Mg or S

    4. Mn2+ or Mn4+

    5. C or Ne

  9. Using the facts that empty, half-filled and fully-filled orbital sets are lower in energy, and that the larger (i.e contianing more electrons) a half-filed or fully-filled orbital set is, the lower in energy it is, rationalize your way to the two most stable oxidation states other than zero for the elements below: (Remember that transition metals always lose their s electrons first.) (10 points)

    1. Bi, Bi3+ and Bi5+

    2. Fe, Fe2+ and Fe3+

    3. Sn, Sn2+ and Sn4+

    4. As, As3+ and As5+

    5. Pb, Pb2+ and Pb4+

    EXTRA CREDIT

  10. Provide the correct Lewis dot structures for the ions ClO-, ClO2-, ClO3- and ClO4-. Looking at these Lewis dot structures, what conclusions can you come up relating them and the increasing acidity of the series HClO, HClO2, HClO3, HClO4. finally, using VSEPR theory predict the structure of each of these ions. (10 points)



    The fewer lone pairs on chlorine, the more acidic the acid in the perchlorate series. Since perchlorate has no lone pairs on chlorine, HClO4 is the most acidic of the series. Hypochlorite has the most lone pairs on chlorine (3 lone pairs), hence HClO is the least acidic of the series.