Which compound is more polar: water or dicloromethane? I know that water is a polar molecule but I don't know the polarity of dicloromethane or how to figure out which one is more polar than the other?
You can get a guess by comparing the electronegativities of the elements.
For example, in H2O, H has EN of about 2.1 and O of about 3.5 for a difference of about 1.4. In dichloromethane, C is about 2.5 and Cl is about 3 for a difference of about 0.5. We might guess from this that water is more polar. This doesn't take into account the 3-D arrangement of the atoms nor the number of different atoms attached to the central atom (2 H to O in H2O and 2 Cl to C in CH2Cl2) but since both dichloromethane and water are essentially tetrahedral and both have the same number of atoms attached to the central atom (the H atoms to C in CH2Cl2 have little difference in EN) then we would stick with water. The only REAL test, I suppose, is to look up the dipole moment of the molecule. Those tables are not widespread and most don't have extensive listings. However, I found water and dichloromethane on the web; water is 1.85 Debye and CH2Cl2 is 1.4 so our best guess was right.
To determine which compound is more polar, we need to consider the molecular structure and polarity of each compound.
Water (H2O) is a bent molecule with a polar covalent bond. The oxygen atom has a higher electronegativity than the hydrogen atoms, meaning it attracts the shared electrons more strongly. This leads to a partial negative charge (δ-) on the oxygen atom and partial positive charges (δ+) on the hydrogen atoms. This polarity gives rise to water's ability to form hydrogen bonds, making it highly polar.
Dichloromethane (CH2Cl2) is a tetrahedral molecule in which chlorine atoms replace two of the hydrogen atoms in methane (CH4). Chlorine has a higher electronegativity than hydrogen but lower than oxygen. Although the C-Cl bonds are polar, the molecule is overall nonpolar because the dipole moments cancel each other out. The chlorine atoms have opposite charges but are symmetrically positioned, resulting in no net dipole moment.
So, to determine which compound is more polar, we compare the polarity of water (highly polar) to that of dichloromethane (nonpolar). Water is more polar due to its bent molecular structure and the presence of hydrogen bonds.
In summary, water is more polar than dichloromethane.