When two or more atoms are joined chemically, they form what?

When two or more atoms are chemically joined together, they form a molecule. A molecule is defined as the smallest fundamental unit of a chemical compound that retains the chemical properties of that compound. Molecules can consist of two or more atoms of the same element or different elements bonded together through chemical bonds, such as covalent or ionic bonds.

For instance, a water molecule (H2O) is made up of two hydrogen atoms and one oxygen atom bonded together, illustrating how molecules can be formed by the combination of different types of atoms. Understanding the distinction between a molecule and other options is vital; for example, a compound is specifically a type of molecule that consists of two or more different elements, but not all molecules are classified as compounds. A mixture, on the other hand, contains two or more substances that are physically combined but not chemically bonded, meaning they retain their individual properties. An element is a pure substance consisting of only one type of atom and cannot be broken down into simpler substances by chemical means.

Thus, the definition of a molecule accurately captures the concept of atoms being linked together, making it the correct answer.