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Answer 1 · 2017-10-03T23:17:31

You calculate the difference in electronegativity between the two atoms in the bond.

The polarity of a covalent bond $X—Y$ $"X—Y"$ is determined by the electronegativity difference $ΔEN$ between the atoms $"X"$ and $"Y"$ .

If the bond is between two identical atoms, the bond is covalent.

For example, $"F—F"$ is a covalent molecule.

$ΔEN = "|3.98 - 3.98|" = 0$

If $ΔEN > 0$ , the bond is polar.

The values of $ΔEN$ can range from 0 to about 3.1, so chemists have assigned arbitrary cut-off points.

Most chemists agree that a covalent bond is polar if $ΔEN$ is between 0.5 and 1.6.

For example, $"H—Cl"$ is a polar covalent molecule.

$ΔEN = "|2.20 - 3.16|" = 0.96$

If $ΔEN > 1.6$ , the bond is considered to be ionic.

For example, $"Na—Cl"$ is an ionic compound.

$ΔEN = "|0.93 - 3.16|" = 2.23$

Between 0 and 0.5, there is so little polarity that the bond is usually called nonpolar.

For a $"C—H"$ bond,

$ΔEN = "|2.55 - 2.20|" = 0.35$

Thus, a $"C—H"$ bond is often called nonpolar even though it is very slightly polar.