1.34 understand that ionic compounds have high melting and boiling points because of strong electrostatic forces between oppositely charged ions

Ionic compounds are held together by strong electrostatic forces that hold them together due to the attraction of the opposing charges (+ and -). To melt or boil anything, heat is used to break the electrostatic forces. The force will get stronger the higher the charge of the ion is, therefore, the stronger the bonds, the more heat needed. Ionic compounds have strong bonds, so they don't melt or boil unless there is a considerable amount of heat, this means they have high melting and boiling points.