Question

How can we know,which molecule is polar and which is non polar molecule?

Answer 1

Polar molecules

Chemical bonding is the result of either an atom sharing one or more outer orbit electrons with another atom or an atom taking outer orbit electrons from the atom with which it is bonding. Normally, an atom has an even distribution of electrons in the orbits or shells, but if more end up on one side that the other in a molecule, there can be a resulting electrical field in that area.

Water is polar

Water is a polar molecule because of the way the atoms bind in the molecule with more positive (+) charges on one side of the molecule and more negative (−) charges on the other side of the molecule. In other words, the Hydrogen atoms group on one side of the molecule, making that more positive (+), such that there are more electrons from the Oxygen atom on the other side of the molecule
.

Water is a polar molecule with positive charges
on one side and negative on the other

Examples of polar molecules

Examples of polar molecules of materials that are gases under standard conditions are:

Ammonia (NH3)

Sulfur Dioxide (SO2)

Hydrogen Sulfide (H2S).

Also, Ethanol is polar, since its oxygen molecule draws electrons towards it due to its high electro-negativity, causing a negative charge around itself.

Non-polar molecules

A non-polar molecule is one in which the electrons are distributed more symmetrically and thus does not have an abundance of charges at the opposite sides. The charges all cancel out each other.



The electrical charges in non-polar Carbon Dioxide are evenly distributed

Examples of non-polar liquids

Most hydrocarbon liquids are non-polar molecules. Examples include:

Toluene

Gasoline

Alkynes are non-polar because they cannot be dissolved in water, as do polar molecules. However, alkynes but do dissolve in other non-polar substances. A rule is that like substances dissolve in like substances.