The reason water is a liquid at room temperature is that the water molecules stick to each other with hydrogen bonds and make it difficult for any one water molecule to break free and evaporate (become a gas). If water was non-polar, it could not form hydrogen bonds and therefore would be a gas at room temperature.

water is called polar molecule, its two hydrogen atoms are joined to one oxygen atom by single covalent bonds, but the electrons of the covalent bonds are not shared equally between oxygen and hydrogen this unequal sharing makes water a polar molecule.

Polar molecules occur when there is an electronegativity difference between the bonded atoms. Nonpolar molecules occur when electrons are shared equal between atoms of a diatomic molecule or when polar bonds in a larger molecule cancel each other out.

Water is a polar molecule with one oxygen atom bonded to two different hydrogen atoms. Due to high electronegativity of oxygen atoms, the covalent bonds formed between oxygen and hydrogen is polar.

(If the difference in electronegativity for the atoms in a bond is greater than 0.4, we consider the bond polar. If the difference in electronegativity is less than 0.4, the bond is essentially nonpolar.) If there are no polar bonds, the molecule is nonpolar.

For a bond to be polar, the electronegativity difference between the two elements needs to be between 0.5 to 1.6. If the electronegativity difference is less than 0.5, the bond is nonpolar. Any more than 1.6 and the molecules become charged ions and form ionic bonds instead.

Simply mix the liquid with an equal part of water and allow the mixture to sit undisturbed. Examine the mixture after the liquids have sat together for a time. If they have not separated, but have formed a solution, the unknown liquid is polar. If there is a clear boundary between the two liquids, it is non-polar.

Polarity is important because it determines whether a molecule is hydrophilic (from the Greek for water-loving) or hydrophobic (from the Greek for water-fearing or water-averse). Molecules with high polarity are hydrophilic, and mix well with other polar compounds such as water.

Some kinds of molecules, like oils and fats, are nonpolar. These nonpolar molecules have no charge, and so water is not very attracted to them. Molecules of nonpolar compounds, such as oil and gasoline, even when mixed well into water, tend to separate from the water when the mixing stops.

Thus water can dissolve table salt (which is made up from Cl- and Na+ ions), and it can dissolve honey (which is neutral but polar) but it cannot dissolve oil (olive oil). Honey is a mostly a mix of sugar molecules (ie fructose and glucose).

Acetone is a polar molecule because it has a polar bond, and the molecular structure does not cause the dipole to be canceled.

Polar solvents have large dipole moments (aka “partial charges”); they contain bonds between atoms with very different electronegativities, such as oxygen and hydrogen. Non polar solvents contain bonds between atoms with similar electronegativities, such as carbon and hydrogen (think hydrocarbons, such as gasoline).