Electron Configurations for Ions

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					                                                                          Electron Configurations for Ions
                                                                          • Main group elements:
                                                                            – Cations – lose electrons from highest energy
                                                                              occupied orbital
                                                                            – Anions – gain electrons in lowest energy
Chapter 6                                                                     unoccupied orbital (Aufbau).
                                                                          • Transition metals (d block)
                                                                            – Form cations
                                                                            – Lose electrons from the outer s orbital before
                                                                              losing electrons from the d orbital



                                                                      1




Octet Rule                                                                Ionic Bonding – Octet Rule
Many elements react to attain a lower energy level (more                          H+
  stable). Many elements want to attain a noble gas
  configuration.

Atoms lose/gain electrons to form ionic compounds.

Atoms share electrons to form covalent compounds.

In both cases, the “outer shell” is fully filled similar to a noble             Lose electrons to            Gain electrons to
   gas electron configuration.                                                  gain noble gas               gain noble gas
                                                                                configuration                configuration
                                                                                            Transition (d orbital)
                                                                                            metals do not attain
                                                                                            noble gas configuration




Ionic Bonding – Octet Rule                                                Covalent Bonding – Octet Rule
                                                                          Share electrons to form an octet in the outer
                                                                           (valence) energy level




           1s     2s       2p          1s   2s      2p



                                       [He]      [Ne]

            Li+ has the electron configuration of He                                    Outer energy level has 8 (or 2)
                                                                                        electrons by sharing electrons
                F- has the electron configuration of Ne
                                                                                Actually it’s really more complicated for covalent
                                                                                         bonds, as we’ll see in chapter 7
Effective nuclear charge (Zeff)                                               Effective nuclear charge (Zeff)
• Nuclear charge is the charge in the nucleus.
   – Number for protons


• Effective nuclear charge is what an
  electron “feels” from the nucleus
   – Electrons affect each other within atoms
   – Electrons can shield one another from the nucleus
   – Multielectron atoms feel a charge less than the
     full nuclear charge




Atomic Radius                                                                 Atomic Radii
   If quantum mechanics tells us we can never know the                                                Decrease radius across row
                                                                                What trends             (increase in p+ and e-)
   exact location of an electron, how do we know where
                                                                                do we see?
                      an atom “ends”?

        Atomic radius: one-half the distance between two
                  nuclei in two adjacent atoms

   More than one specific definition of radius depending on the type of             Increase
   bonding involved. So, the same element can actually have different             radius down
             radii. The ones we use in class are an average.                         column
                                                                                 (increase in p+
                                                                                     and e-)




                Van der Waals radius          Covalent Radius
                                                                                                            d-block removed
                                                                          9




Atomic Radii                                                                  Trends in Ionic Radii
                                         Increase in Zeff                       How are the
   Why do we                                                                   trends in ionic
    see two
                                                                                     radii
    different
    trends?
                                                                               different/same
                                                                                  as atomic
                                                                                    radii?




    Increase in
   energy levels




                                           d-block removed                                            d-block removed
                                                                                                                                   12
Atomic and Ionic Radii                                            Ionic Radius
                                                                  Cations:                                            Anions:
                           The radii of metals decrease
                             when they become ions
                                                                      –Outer electrons in lower                           –Outer electrons are in the
                                                                      energy level (closer to the                         same energy level as
                          The radii of non-metals increase            nucleus)                                            before
                              when they become ions                   –Increase in Zeff for                               –Decrease in the Zeff for
                                                                      remaining outer electrons                           outer electrons because of
                                                                      –Outer electrons pulled in                          sheilding by more electrons
                           Within the cation/anions, the                                                                  in the same energy level
                                                                      closer
                                 trends till holds.

                             Between the two groups,
                          however, the relative sizes have
                                     changed




Ionization Energy                                                 Ionization Energy
                                                                  •What is the correlation?
• Energy to remove valence electron from
  neutral atom in the gas phase                                   •Why?
                                                                                             Atomic Radii and First Ionization Energies
                                                                                               of the Alkali Metal (Group 1) Elements

• X(g) → X+(g) + e-                                                                               550
                                                                              Ionozation Energy



                                                                                                              Li
                                                                                                  500
                                                                                   (kJ/mol)




                                                                                                  450                Na
   – Positive because is required to remove atom                                                  400
                                                                                                                             K          Rb

   – More energy to remove an electron from a                                                     350                                        Cs
     noble gas configuration                                                                      300
                                                                                                        140        190           240              290
                                                                                                                   Atomic Radius (pm)


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Trends in First Ionization Energy                                 Anomalous IE1
                                                                          Notice an
 • Which member of each pair has the larger                         unexpected trend in
   first ionization energy? Why?                                       1st ionization
                                                                   energies across rows
 •F          or Cl
 •O          or F                                                       In most
                                                                      cases, the
 • Na        or Mg                                                    smaller the
                                                                      radius, the
 •K          or Na                                                    higher the
 •N        or   O (this one might be a trick)                        1st ionization
                                                                         energy

                                                                        Why an
                                                                       anomaly?
                                                             20
Anomalous first ionization energies (IE1)                                             Successive Ionization Energies
                                                                                       • Successive ionization energies take….more energy. Why?
                 N                             O                                       • And certain, ionization energies for certain atoms take a lot more energy.
                                                                                         Why?
          Larger atom:               Smaller atom                  Does not fit
                75 pm                      73 pm                  the expected
                                                                      trend
           Larger IE1:                   Smaller IE1:
          1402 kJ/mol                    1314 kJ/mol


                                                                    Takes more
                                                                      energy to
                                                                     remove an
     2s              2p             2s             2p             electron from a
                                                                    half-filled or
      1st ionization                1st ionization
                                                                  completely filled
           of N                          of O                          subshell




                                                                                      Electron Affinity
                                                                                      • Energy released when electron is added
                                                                      Takes much
                                                                    more energy to      to neutral atom in the gas phase
           2p             3s              2p                           remove an
                                                         3s
                                                                    electron from a
  1st Ionization of Na               2nd Ionization of Na               noble gas
                                                                     configuration
                                                                                      • X(g) + e- → X-(g)

                                                                                         – Generally negative because energy is
                                                                                               released
           2p             3s         2p             3s              2p        3s         – More energy released, higher affinity for
  1st Ionization of Mg         2nd Ionization of Mg           3rd Ionization of Mg         electron




Electron Affinity                                                                     Anomalous electron affinities
                                                                                                 N                        Be                        Ne
          Trend is not as smooth as others. Many exceptions


                                                                          Why is
                                                                         nitrogen
                                                                         positive?
                                                                                          2s         2p             2s         2p              2p          3s

                                                                                        Adding an electron Adding an electron
                                                                                         to a half-filled p    to a filled s                  Adding an
                                                                                             subshell            subshell                    electron to a
                                                                                            sometimes       destabilizes the                   noble gas
                                                                                         destabilizes the    atom. Or, the                   configuration
                                                                                          atom. Or, the       atoms is less                     greatly
                                                                                        atom is less stable    stable than                  destabilizes the
                               Positive or small
                                                                                          than predicted        predicted                        atom
                               negative number
                                                           Lattice Energy:
                         (magnitude)                          – First, look at the charges
                                                                 • Charges = Energy




                                        (magnitude)
                                                              – Then, look at radii
                                                                 • Radii = Energy




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Relative Lattice Energies
• Which compound in each pair has the highest
  lattice energy?
   – NaCl or MgCl2
   – MgO or Na2O
   – NaCl or KCl
   – NaBr or NaCl




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