Final answer:
An ionic compound typically consists of metal and nonmetal elements or contains polyatomic ions, and has a neutral overall charge due to the balanced ratio of cations to anions. Compounds that dissociate into ions in water and conduct electricity in solution, but not in solid form, are also ionic.
Step-by-step explanation:
To determine if a compound is ionic, you can apply a general rule of thumb which involves examining the elements that make up the compound. Here are the main points for identifying an ionic compound:
- Ionic compounds are typically formed between metals and nonmetals. If the compound has a metal and a nonmetal, it is likely ionic.
- The formula of an ionic compound represents the simplest whole-number ratio of the atoms of the constituent elements, which gives a neutral overall charge.
- If the chemical formula contains a known polyatomic ion, such as NO3- for nitrate, it suggests the compound is ionic.
- Ionic compounds must be electrically neutral, so the total number of positive charges from the cations must equal the total negative charges from the anions.
- Ionic compounds dissociate into ions in water and solutions of ionic compounds conduct electricity (whereas solid ionic compounds do not).
Therefore, a substance is ionic if it consists of a combination of cations (metal ions) and anions (nonmetal or polyatomic ions) that result in a neutral overall charge. The cations and anions must be in the correct ratio to balance each other out, like in aluminum oxide, Al2O3, with two Al³+ cations for every three O²− anions.