How to Know If Covalent Compounds Are Polar or Nonpolar
- 1). Find each element in the compound on an electronegativity chart. Compare their electronegativity values to determine whether there is a significant difference between the elements. If there is, then the compound forms polar bonds and may create a polar molecule.
For example, hydrogen has an electronegativity of 2.1 whereas oxygen has a value of 3.5. The difference between these numbers indicates that water (H2O) forms polar bonds. - 2). Write the chemical symbol of the most electronegative element, then surround it with the symbols of the other elements. Draw a straight line between the central atom and each outer atom to represent a chemical bond. This forms the skeleton of a Lewis dot structure.
- 3). Add the number of electrons possessed by each element in the molecule, then subtract two electrons for each bond. The result is the number of electrons left to distribute around the atoms. You can find the number of electrons in each element by looking up its atomic number on the periodic table.
- 4). Distribute the electrons around the central atom first, until it has a total of eight. Remember that each bond represents two electrons.
- 5). Distribute the remaining electrons around the outer elements.
- 6). Create double or triple bonds if both the outer and central atoms have unbonded pairs of electrons nearby.
- 7). Count the number of bonds and the number of unbonded pairs around the central atom.
- 8). Compare this number to a molecular geometry chart, which compares the number of bonds and unbonded pairs to the shape of the molecule. Determine what the shape of the molecule is.
For example, the oxygen atom in a water molecule has two bonded pairs and two lone pairs, which gives it a bent shape where each of the hydrogen atoms are less than 109.5 degrees apart. - 9). Examine the shape of the molecule to determine whether it is symmetrical or asymmetrical. If it is asymmetrical, the more electronegative atoms will be on one end of the molecule and the fewer electronegative atoms will be concentrated on the other end. This arrangement forms a polar molecule. If the atoms are arranged symmetrically, so that no side is more electronegative than another, it is non-polar.
For example, because water's oxygen atom is on one end and both of its hydrogen atoms are on the other end, the molecule is asymmetrical -- and so, water is polar.
