When boiling an ionic substance, you typically overcome the ionic bond rather than breaking it. Ionic bonds are formed through the electrostatic attraction between positively and negatively charged ions. When the substance is heated, the added energy increases the kinetic energy of the ions, causing them to move more rapidly. Eventually, the thermal energy becomes sufficient to overcome the attractive forces between the ions, leading to the separation of the ions and the conversion of the solid or liquid ionic compound into a gaseous state.
In the case of simple covalent compounds, such as molecules held together by covalent bonds, the boiling process involves overcoming the intermolecular forces between the molecules. Intermolecular forces, such as London dispersion forces, dipole-dipole interactions, and hydrogen bonding, are the attractive forces between neighboring molecules. When the compound is heated, the thermal energy increases, causing the molecules to move more rapidly. As the temperature approaches the boiling point, the kinetic energy becomes sufficient to overcome these intermolecular forces, leading to the conversion of the liquid into a gaseous state. So, in this case as well, the intermolecular forces are overcome rather than broken.