.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "api/gallery/structure/lewis/plot_02_kossel_oxidation_states.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_api_gallery_structure_lewis_plot_02_kossel_oxidation_states.py>`
        to download the full example code.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_api_gallery_structure_lewis_plot_02_kossel_oxidation_states.py:


Kossel's ionic bond: oxidation states as the fully ionic limit
==============================================================

Walther Kossel (1916) described bonding as the complete transfer of
electrons from one atom to another, leaving ions with noble-gas
configurations held together by electrostatic attraction. Oxidation
states are the bookkeeping version of that picture: give every bonding
pair entirely to the more electronegative atom (sharing only between
identical atoms) and compare the electron count with the free atom.

For a salt such as NaCl or MgO this recovers the real ionic charges. For
covalent molecules it gives the charges the atoms *would* carry if the
bonds were fully ionic. The example below follows oxygen through
:math:`\mathrm{H_2O}`, :math:`\mathrm{H_2O_2}`, :math:`\mathrm{O_2}` and
:math:`\mathrm{OF_2}`, where it ranges from -2 to +2 depending on which
partner is more electronegative, using
:meth:`~chemistrykit.structure.systems.lewis.LewisStructure.oxidation_states`.

.. GENERATED FROM PYTHON SOURCE LINES 22-39

.. code-block:: Python

    import matplotlib.pyplot as plt

    from chemistrykit.structure.systems.lewis import LewisStructure

    ionic = {
        "NaCl": LewisStructure(["Na", "Cl"], {(0, 1): 1}, {1: 3}),
        "KF": LewisStructure(["K", "F"], {(0, 1): 1}, {1: 3}),
        "MgO": LewisStructure(["Mg", "O"], {(0, 1): 2}, {1: 2}),
        "CaO": LewisStructure(["Ca", "O"], {(0, 1): 2}, {1: 2}),
    }
    print("Salts: the ionic limit gives each ion's real charge")
    for name, s in ionic.items():
        ox = s.oxidation_states()
        print(f"  {name:5s}: " + ", ".join(f"{sym} {ox[i]:+.0f}" for i, sym in enumerate(s.symbols)))
    assert ionic["NaCl"].oxidation_states() == {0: 1.0, 1: -1.0}
    assert ionic["MgO"].oxidation_states() == {0: 2.0, 1: -2.0}





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    Salts: the ionic limit gives each ion's real charge
      NaCl : Na +1, Cl -1
      KF   : K +1, F -1
      MgO  : Mg +2, O -2
      CaO  : Ca +2, O -2




.. GENERATED FROM PYTHON SOURCE LINES 40-44

Oxygen's oxidation state in four molecules. Bonds to hydrogen give the
electrons to oxygen, an O-O bond splits them evenly, and bonds to
fluorine (the only element more electronegative than oxygen) give them
away:

.. GENERATED FROM PYTHON SOURCE LINES 44-57

.. code-block:: Python


    oxygen_compounds = {
        "H2O": (LewisStructure(["O", "H", "H"], {(0, 1): 1, (0, 2): 1}, {0: 2}), 0),
        "H2O2": (LewisStructure(["H", "O", "O", "H"], {(0, 1): 1, (1, 2): 1, (2, 3): 1}, {1: 2, 2: 2}), 1),
        "O2": (LewisStructure(["O", "O"], {(0, 1): 2}, {0: 2, 1: 2}), 0),
        "OF2": (LewisStructure(["O", "F", "F"], {(0, 1): 1, (0, 2): 1}, {0: 2, 1: 3, 2: 3}), 0),
    }
    oxygen_state = {}
    for name, (s, o_index) in oxygen_compounds.items():
        oxygen_state[name] = s.oxidation_states()[o_index]
        print(f"{name:5s}: O oxidation state {oxygen_state[name]:+.0f}, formal charge on O {s.formal_charges()[o_index]:+.0f}")
    assert [oxygen_state[k] for k in oxygen_compounds] == [-2.0, -1.0, 0.0, 2.0]





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    H2O  : O oxidation state -2, formal charge on O +0
    H2O2 : O oxidation state -1, formal charge on O +0
    O2   : O oxidation state +0, formal charge on O +0
    OF2  : O oxidation state +2, formal charge on O +0




.. GENERATED FROM PYTHON SOURCE LINES 58-61

The formal charge on oxygen is zero in all four, because formal charge
is Lewis's even-sharing limit; the oxidation state is Kossel's ionic
limit, and only it follows the partner's electronegativity.

.. GENERATED FROM PYTHON SOURCE LINES 61-70

.. code-block:: Python


    fig, ax = plt.subplots(figsize=(6, 4))
    names = list(oxygen_state)
    ax.bar(names, [oxygen_state[n] for n in names], color=["C0", "C1", "C2", "C3"])
    ax.axhline(0.0, color="gray", linewidth=0.8)
    ax.set_ylabel("oxidation state of O")
    ax.set_title("Kossel's ionic limit: oxygen from -2 to +2")
    fig.tight_layout()
    plt.show()



.. image-sg:: /api/gallery/structure/lewis/images/sphx_glr_plot_02_kossel_oxidation_states_001.png
   :alt: Kossel's ionic limit: oxygen from -2 to +2
   :srcset: /api/gallery/structure/lewis/images/sphx_glr_plot_02_kossel_oxidation_states_001.png
   :class: sphx-glr-single-img






.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (0 minutes 0.031 seconds)


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  .. container:: sphx-glr-footer sphx-glr-footer-example

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