Answer the following question given this paragraph: 

Ionic substances are completely held together by ionic bonds. The full charges of the ions (for example, Na + and Cl - in sodium chloride) cause electrostatic interactions that result in a stable crystal lattice. We saw in the previous chapter that most ionic compounds have high melting points, are brittle, are often soluble in water, and conduct electricity when melted or dissolved in water. Ionic compounds exist as extended, orderly arrangements of ions. As we will see, this is quite different from the structure of molecular substances, which take the form of collections of individual molecules. The atoms within a molecule are held very strongly together, but the interactions between different molecules are significantly weaker.


Q: What are ionic substances completely held together by?


A:
ionic bonds