Activity 2: Intermolecular forces (IMF) present among species Polar substances exhibit dipole-dipole interaction due to the presence of (+) and (-) ends of the molecules. In the exercise above, sulphur dioxide (SO₂) has polar ends that will participate in the dipole-dipole forces of attraction. With the presence of an ion (cation or anion), the charged ends of polar molecules will be attracted to the dipole. This is true in the case of Na+ and formaldehyde. The positive (+) sodium ion will be attracted to the partially-negative oxygen in formaldehyde, resulting to an ion-dipole interaction. For the third example, CO₂ is a nonpolar substance. It is a linear molecule and the electron shift at the right of C is balanced by the electron shift to the left. This produces no net shift in electron density so no net charged is produced. For nonpolar molecules, only dispersion forces are present. In both NH3 and H₂O, the hydrogen atoms are bonded to more electronegative atoms, nitrogen and oxygen, respectively. This permits them to form H-bonds with other molecules with the same condition. Thus, H-bond is present between NH3 and H₂O. Ion-induced dipole forces of attraction are present among Fe2+ ions together with oxygen molecules. The charge in iron will distort the electron distribution in O₂ resulting to temporary poles in oxygen. The oppositely-charged particles, Fe²+ and partially-negative end of Oz will then be attracted to form the above-mentioned force of attraction. In all of the examples above, London dispersion forces are also present.​