How are ionic and molecular compounds similar and different?

There are a lot more differences than similarities between ionic and molecular , but let's start with the similarities.

Both have a non-metal in them and both compounds are formed by the atoms trying to achieve a state of 8 (or 2) electrons in their valence (outer) shell.

The differences are numerous and basically define the two branches of chemistry, inorganic and organic. are inorganic. They are formed by combining metals (+ ions) with nonmetals (- ions).

They are soluble in water (polar), conduct electricity in solution, and have high melting (freezing) and boiling points. Organic compounds are molecular also called covalent. They are formed by nonmetals sharing their outer shell electrons. Most are not soluble in water. Even if they dissolve they do not conduct electricity. They have low melting and boiling points. In fact most are liquids and gases at room temperature.