A compound is a substance formed when two or more different elements chemically bond together. For example, when hydrogen and oxygen combine, they create water, a compound essential for life. Compounds can have very different properties from the individual elements that make them up, like how salt (sodium chloride) is safe to eat, while its components, sodium and chlorine, are harmful on their own. Compounds can be found all around us, from the air we breathe to the food we eat. They can be classified into two main types: ionic compounds, which form when atoms transfer electrons, and covalent compounds, where atoms share electrons. Understanding compounds helps us learn about the world and how different substances interact.