CHM1011 questions

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CHM1011 questions
2015-06-10 03:04:30
chemistry mock exam 1 questions
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  1. Use this diagram to explain why the energy of 3s atomic orbital is lower than the energy of the 3p atomic orbital
    The region shaded in on the graph above indicates that an electron in the 3s atomic orbital has more penetration than an electron in the 3p atomic orbital (closer to the nucleus and thus more stable) so this (s) electron shields the 3p electron from the nucleus.
  2. Define the exclusion principle
    • States that any atomic orbital can hold up to a maximum of 2 electrons and must have opposing values for Ms= +- 1/2
    • (exclusion= one excludes the other= + and -)
  3. Define the aufbau principle
    • States that for atoms in the ground state, orbitals are filled in order of increasing energy
    • Aufbau sounds like Babaw= up= increasing energy
  4. Define Hund's rule
    • States that for a set of degenerate orbitals there must be at least one electron in each orbital before electron pair can occur
    • hunds= sounds like hands= 2 hands= use 1 hand at a time= 1 electron per orbital
  5. The first ionization energy for the elements are observed to increase as the atomic number increases. Give an explanation for this observation
    From left to right across the periodic table, the effective nuclear charge (Zeff) (the net positive charge experienced by an electron in a multi-electron atom) increases, thus the outer electrons experience a stronger nuclear attraction and are more difficult to remove 
  6. Explain the trend in atomic radii
    • Since the atomic nuclear charge increases from left to right, the outer electrons experience greater nuclear attraction and are closer to the nucleus.
    • Thus atomic radius decreases
  7. How to find bonding order
    • BO=    #bonding pairs of e-s
    •              #chemical bonds
  8. Does the NO3- anion have a permanent dipole moment?
    • No, the structure is more like
    • In combination with the trigonal planar geometry, this delocalisation means it is non polar
  9. How to tell if a molecule is diamagnetic or paramagnetic from an MO diagram
    • If there are no unpaired electrons (all electrons paired), then it is diamagnetic
    • dia=2=pairs
  10. What is the first law of thermodynamics?
    Energy can be converted from one form into another for example into heat or used to do work, but it cannot be created or destroyed
  11. Express the 2nd law of thermodynamics
    • Whenever a spontaneous event takes place in the Universe, the total entropy of the Universe increases, ∆S universe >O
    • ∆Suniverse =∆Ssystem + ∆Ssurroundings
  12. An increase in temperature increases the rate of virtually all reactions
    • Increase in temperature increases the kinetic energy of all molecules therefore
    • Particles collide more frequently
    • Possess greater energy when they collide