Contrast ionic and molecular substances in terms of the types of attractive forces that govern their behavior.

To contrast ionic and molecular substances, we need to understand the types of attractive forces that govern their behavior.

Ionic substances are formed from the transfer of electrons between atoms. This results in the formation of oppositely charged ions, such as Na+ and Cl-. The attractive forces that govern their behavior are electrostatic forces of attraction between the positive and negative ions. These forces are very strong and result in the formation of a crystal lattice structure. The electrostatic attractions are present in all directions, giving ionic substances high melting and boiling points. Examples include sodium chloride (NaCl) and potassium iodide (KI).

On the other hand, molecular substances are formed from the sharing of electrons between atoms. This sharing creates covalent bonds, and each molecule is held together by these bonds. The types of attractive forces that govern their behavior are intermolecular forces, which are weaker compared to the ionic electrostatic forces. There are various types of intermolecular forces such as London dispersion forces, dipole-dipole interactions, and hydrogen bonding. These forces are directional and act between different molecules. Molecular substances generally have lower melting and boiling points compared to ionic substances. Examples include water (H2O) and methane (CH4).

In summary, ionic substances are held together by strong electrostatic attractions between positive and negative ions, while molecular substances are held together by weaker intermolecular forces between molecules.