Covalent compounds are formed when two or more nonmetal atoms share electrons to achieve stability. This sharing allows each atom to fill its outer electron shell, which is essential for chemical stability. Common examples of covalent compounds include water (H₂O) and carbon dioxide (CO₂), where the atoms are held together by strong covalent bonds. These compounds can exist in various forms, such as gases, liquids, or solids, depending on the strength of the bonds and the arrangement of the atoms. Covalent compounds often have lower melting and boiling points compared to ionic compounds, making them unique in their physical properties.