Are Be(OH)2 and CF3Cl polar or non-polar? What is the reason?

3 Answers

  • I’d call both nonpolar


    (1) look at electronegativities to determine if the bonds are polar

    (2) look for symmetry. a molecule with polar bonds is NON polar if it is symmetric!


    here’s a table of EN

    http://en.wikipedia.org/wiki/Electronegativity

    when it comes groups.. like -OH.. things get a bit more complicated. Oone of the simpliest approximations is

    http://pages.unibas.ch/mdpi/ecsoc/e0002/calelecg.h

    in -O-H.. the are 2 O bonds (2×3.44) & 1 H bond (1×2.20) for a total EN of (2*3.44+1×2.20)/3 = 3.03

    The rules of thumb for determining the type of bond go..

    if ΔEN < 0.5, the bond is nonpolar covalent

    if 0.5 < ΔEN < 1.5, the bond is polar covalent

    if 1.5 < ΔEN < 2.0 AND no metal is present, the bond is polar covalent

    if 1.5 < ΔEN < 2.0 AND a metal is present, the bond is ionic

    if 2.0 < ΔEN, the bond is ionic

    and again.. those are rules of thumb

    in Be(OH)2.. .the Be-OH bond had ΔEN = 3.03 – 1.57 = 1.46… so this should be a polar covalent bond

    in CF3Cl, ΔEN between C and F = 3.98 – 2.55 = 1.43.. ΔEN between C and Cl is 3.16 – 2.55 = 0.61.. and all the bonds are polar covalent


    as to symmetry…

    it turns out Be(OH)2 is in fact a linear molecule.. H-O-Be-O-H.. so it has "electronic symmetry" and the different areas of high electron density cancel out.

    CF3Cl is also a symmetric molecule. it’s shape is tetrahedron. and therefore is non polar..


    now both molecules will actually have areas of partial charges.. F has a higher EN than Cl so it will withdraw slightly more electron density from the carbon than the Cl will. But what we’re doing here is looking at a broad range of values and drawing lines in the sand and saying if you’re on this side your polar and on that side your not. Get it? I think CF3Cl is on the non polar side of that line.


    in any case..

    polar molecules must have polar bonds

    polar molecules cannot have electronic symmetry.


    how about that.. 3 of the usual answerers here on YA. 3 different answers.

  • CF3Cl is polar because this forms a tetrahedral molecule, but because you have different substituents, there is a net dipole moment in the molecule.

    I would consider Be(OH)2 to be an ionic compound. I don’t think ionic compounds are generally considered to be either polar or non-polar.

  • Be(OH)2 is linear thus canceling any effect of polar bonds

    CF3Cl is tetrahedral with one corner occupied by F which is more electronegative than the Cl’s

    so it is somewhat polar

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