# Dipoles

Electronegativity and Polarity

Tip: This isn't the place to ask a question because the teacher can't reply.

## Key Questions

Molecular dipoles exist if one or more of the atoms is more electronegative than the other(s)

#### Explanation:

The most common dipole is water.

Since $O$ is more electronegative than $H$ the shared electrons tend to be more in the neighbourhood of the $O$-atom.
Since the molecule is 'bent' they tend to be more in the upper part of the figure above. This gives a slight negative charge (called $\delta -$) at the top, and a $\delta +$ at the $H$-arms.

Since $+$ and $-$ attract, the next molecule will tend to turn one of its $H$ 's toward the $O$ of the first one.

This polarity also has many consequences for the behaviour of a polar liquid like boiling point, solvability, etc. and even the shape of snow flakes.

There are 3 types of Molecular Dipoles.

#### Explanation:

Permanent dipoles: These occur when two atoms in a molecule have substantially different electro negativity: One atom attracts electrons more than another, becoming more negative, while the other atom becomes more positive.

Instantaneous dipoles: These occur due to chance when electrons happen to be more concentrated in one place than another in a molecule, creating a temporary dipole.

Induced dipoles: These can occur when one molecule with a permanent dipole repels another molecule's electrons, inducing a dipole moment in that molecule.

A molecule is polarized when it carries an induced dipole.

Dipoles occur when there is a relative charge on each side of a molecule induced by the bond electronegativities.

#### Explanation:

The dipole moment of an entire molecule is made up of two bond moments -vector quantities having both magnitude and direction. Thus, a measured dipole moment is equal to the vector sum of the bond moments that comprise it.

Bond moments are vector quantities, possessing both magnitude and direction. Therefore, it's possible for a molecule to have bond moments and yet to be non-polar, if the individual bond moments in the molecule are equal in magnitude but opposite in their direction, therefore cancelling each other out. Thus, the sum is 0 and there is no dipole moment. An example of a molecule with bond moments and that is non-polar is CO2. You could have a linear molecule with the same atom on either side of the central atom that cancel each other out.

## Questions

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