Question

How do we draw the dipole moment of a water molecule?

Answer 1

Looking at the electronegativity and shape of the `"H"_2"O"` molecule tells you how the arrow depicts the polarity: from in between the hydrogen atoms to the oxygen atom. (See explanation)

Explanation:

We start by looking at a water molecule:

As we can see, the 2 hydrogen atoms are covalently bonded to the oxygen atom, which has two lone pairs (4 total electrons that push the H atoms further away).

Oxygen is a much more electronegative atom than hydrogen, meaning that it attracts the electrons more than hydrogen does.

So there is a higher density of electrons around the oxygen atom, giving it an overall negative charge, and the hydrogen atoms have overall positive charges.

An arrow to show the polarity points from the positive areas to the negative areas. Looking at the two H atoms separate, we would then draw an arrow from each H atom (the positive area) to the O atom (the negative area):

When we put these two arrows together, they yield a single arrow that goes from the point in-between the two H atoms up to the O atom, like so: (indicated by the red arrow)