Lewis Dot Structures help?

What would lewis dot structures look like for the following molecules or polyatomic ions:

PH3, phosphine

BF3, boron trifluoride

SO3/2 silfite ion

SeF4, selenium tetrafluoride

Please be detailed. Thank you :]

Comments

  • PH3 - three single bonds, all P-H. One unshared pair on the P

    BF3 - three single bonds, all B-F. Note: only 6 electrons in valence shell of B. Each F has three unshared pairs.

    SO3^2-

    The S is central to the three oxygens. One oxygen has a db to the S and also has two unshared pairs. The other two oxygens each have a single bond to the S and also have three unshared pairs. Each of these last two oxygens bears a negative charge. The sulfur has an additional unshared pair of electrons.

    There are three resonance forms to the above structure. The bond order for each S-O bond is 1.33.

    SeF4 - I'll take a different tack here. The molecular geometry is disphenoidal and is given the generic formula of AX4E. There are 4 single bonds and one unshared pair on the Se.

    Best wishes on the Lewis structure.

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