A chemical compound is a substance formed when two or more different elements chemically bond together. These elements combine in fixed ratios, resulting in unique properties that differ from those of the individual elements. For example, when hydrogen and oxygen combine, they form water, a compound essential for life. Compounds can be classified into two main categories: ionic and covalent. Ionic compounds, like sodium chloride (table salt), consist of positively and negatively charged ions. In contrast, covalent compounds, such as carbon dioxide, are formed when atoms share electrons. Understanding chemical compounds is fundamental in fields like chemistry and biochemistry.