# How do you determine if a molecule has a polar covalent bond based on the lewis dot structure?

Nov 17, 2016

When you draw the lewis dot structure can you draw a circle around both atoms that represent a stable inert gas structure.

#### Explanation:

In a covalent bond the electrons are shared between both atoms, in a roughly equal manner. If the electron structures for both atoms are stable after sharing they will share the electrons covalently.

$C {O}_{2}$ as an example

.. ..
: O :: C :: O :

If you draw a circle around either Oxygen it will have 8 electrons a stable structure. The four electrons from the double bond and the four electrons from the two pairs of unshared electrons on the Oxygen.

If you draw a circle around the Carbon it will have 8 electrons a stable structure. The two sets of four electrons from the double bonds joining the Carbon to the two Oxygens.

$N a C l$ as an example
..
Na: Cl:
..

If you draw a circle around the Sodium it has only 2 electrons which is not a stable structure. The Sodium will lose the 2 electrons that form the bond with Chlorine. The losing rather than sharing the electrons creates an ionic bond.

Dec 23, 2016

You calculate the electronegativity differences (ΔEN) between the central atom and the atoms that are directly attached to it.

#### Explanation:

For example, the Lewis structure of ${\text{CO}}_{2}$ is

Look up the electronegativities of $\text{C}$ (2.55) and $\text{O}$ (3.44).

ΔEN = "3.44 - 2.55" = 0.89

This value is greater than 0.5, so the $\text{C=O}$ bond is polar covalent.

Now consider the Lewis structure for ${\text{PH}}_{3}$:

The electronegativities are $\text{P} = 2.19$ and $\text{H} = 2.20$.

ΔEN = "2.20 - 2.19" = 0.01

This is about as nonpolar as you can get for a bond between two different atoms.

Conclusion: ${\text{PH}}_{3}$ has no polar bonds.