BF3 (Boron Trifluoride) is neither positive nor negative as a whole molecule. It is electrically neutral. While it contains polar bonds, the molecule's symmetrical shape cancels out the individual bond dipoles, resulting in a nonpolar molecule overall.
Understanding BF3's Polarity
To understand why BF3 is nonpolar despite having polar bonds, consider the following:
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Polar Bonds: Boron (B) and Fluorine (F) have different electronegativities. Fluorine is significantly more electronegative than Boron. This difference in electronegativity creates polar covalent bonds between Boron and each Fluorine atom. Each B-F bond has a dipole moment, with the Fluorine atom having a partial negative charge (δ-) and the Boron atom having a partial positive charge (δ+).
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Molecular Geometry: BF3 has a trigonal planar molecular geometry. This means the three Fluorine atoms are arranged symmetrically around the Boron atom, with bond angles of 120 degrees.
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Dipole Moment Cancellation: Because of the symmetrical trigonal planar geometry, the three bond dipoles cancel each other out. Each B-F bond dipole pulls equally in three different directions, resulting in a net dipole moment of zero for the entire molecule.
Summary
Although the individual bonds in BF3 are polar, the symmetrical arrangement of the Fluorine atoms around the Boron atom causes the bond dipoles to cancel each other out. This results in a nonpolar molecule, meaning it doesn't have a positive or negative "side".
