Chemical compounds are substances formed when two or more different elements bond together in specific proportions. For example, water is a chemical compound made of two hydrogen atoms and one oxygen atom, represented by the formula H2O. These compounds can have unique properties that differ from the individual elements that make them up, such as how salt (NaCl) tastes very different from sodium and chlorine. Compounds can be classified into two main categories: ionic and covalent. Ionic compounds, like NaCl, form when atoms transfer electrons, while covalent compounds, such as H2O, form when atoms share electrons. Understanding these compounds is essential in fields like chemistry, biology, and environmental science.