Atoms are the basic building blocks of matter and are made up of three subatomic particles: protons, neutrons, and electrons. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. Atoms are identified by the number of protons they have in their nucleus, which is called the atomic number.
Elements are substances that are made up of only one type of atom. They are identified by their atomic number and are arranged on the periodic table of elements in order of increasing atomic number. Elements have unique properties, such as their melting point, boiling point, and reactivity.
Compounds are substances that are made up of two or more different elements chemically combined in a fixed ratio. Compounds have unique properties that are different from their component elements, and they can be broken down into their constituent elements through chemical reactions. The elements in a compound are held together by chemical bonds, which can be covalent, ionic, or metallic. Examples of compounds include water (H2O) and sodium chloride (NaCl).