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

• 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

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.