## Polarity

Ashley McClearnen 1B
Posts: 59
Joined: Fri Sep 28, 2018 12:26 am

### Polarity

When trying to figure out if a molecule is polar, I know it is helpful to draw the Lewis structure. If the Lewis structure has a lone pair, does that mean it is polar or not necessarily?

Danielle_Gallandt3I
Posts: 70
Joined: Fri Sep 28, 2018 12:24 am

### Re: Polarity

Not necessarily. It depends on the overall molecular geometry. If the dipole moments cancel out due to molecular geometry then it is nonpolar. This is the case if the molecular geometry is linear, because the dipole moments would go toward the center so no one part of the molecule has a significant charge over the other.

Dana Wilks 3I
Posts: 30
Joined: Fri Sep 28, 2018 12:23 am

### Re: Polarity

For example, the lewis structure for carbon dioxide has 2 lone pairs on both the oxygen atoms. To be as far away from each other as possible the two oxygen atoms are opposite each other so their dipole moments cancel out.

Veronica Soliman 4H
Posts: 51
Joined: Fri Sep 28, 2018 12:28 am

### Re: Polarity

It's polar if it's got a dipole moment which means the little arrow with a plus sign points toward the more electronegative element (usually oxygen, occasionally carbon...etc)

Danielle_Gallandt3I
Posts: 70
Joined: Fri Sep 28, 2018 12:24 am

### Re: Polarity

Veronica Soliman 4H wrote:It's polar if it's got a dipole moment which means the little arrow with a plus sign points toward the more electronegative element (usually oxygen, occasionally carbon...etc)

This is only polar if the dipole moments do not cancel out. You can have a situation where there are dipole moments and it is nonpolar, as long as these all cancel out
Last edited by Danielle_Gallandt3I on Mon Jan 14, 2019 5:59 pm, edited 1 time in total.

Ashita Tanwar 3H
Posts: 30
Joined: Fri Sep 28, 2018 12:23 am

### Re: Polarity

Also, how do you figure out if a molecule is polar if there are no lone pairs? Do you use the formal charges?

Veronica Soliman 4H
Posts: 51
Joined: Fri Sep 28, 2018 12:28 am

### Re: Polarity

Danielle_Gallandt3I wrote:
Veronica Soliman 4H wrote:It's polar if it's got a dipole moment which means the little arrow with a plus sign points toward the more electronegative element (usually oxygen, occasionally carbon...etc)

This is only polar if the dipole moments cancel out. You can have a situation where there are dipole moments and it is nonpolar, as long as these all cancel out

The dipole moments should not cancel out if it is polar otherwise that would make it nonpolar.

Jchellis 1I
Posts: 61
Joined: Fri Sep 28, 2018 12:15 am

### Re: Polarity

If the molecule has no lone pairs then you can tell if it is polar based off of its electronegativity