Final answer:
Ionic compounds conduct electricity when molten, have high melting points, and generally are soluble in water, while molecular compounds tend to have lower melting points and poor conductivity.
Step-by-step explanation:
When trying to determine if unknown substances are held together by ionic bonds or form molecules with covalent bonds, examining their behaviors can provide clues.
Ionic compounds usually consist of metals and non-metals, they're often soluble in water, have high melting and boiling points, and can conduct electricity when molten or dissolved in solution due to the presence of mobile ions. In contrast, molecular compounds, which are held together by covalent bonds, are mostly made up of non-metals, generally have lower melting and boiling points, and poor electrical conductivity in any state.
They are formed by atoms sharing electrons rather than transferring them. Polar covalent bonds have some ionic character due to unequal sharing of electrons, but they still constitute covalent bonding. Metallic bonds are distinct and characterized by a sea of electrons allowing metals to conduct electricity and be both malleable and ductile. Covalent network solids, on the other hand, are extremely hard, have high melting points, and generally do not conduct electricity.