Difference between atom, molecule and compound in chemistry with examples

In chemistry, "atom," "molecule," and "compound" are fundamental terms that describe different levels of chemical structure and composition. Here are the key differences between them, along with examples:

Atom

• An atom is the smallest unit of matter that retains the chemical properties of an element.
• Atoms consist of a nucleus at the center, containing protons and neutrons, surrounded by electrons in electron shells or energy levels.
• Atoms are the building blocks of all matter and are chemically indivisible for a given element.

Example of an Atom:

• Hydrogen atom (H): A hydrogen atom consists of one proton in its nucleus and one electron in its electron shell.

Molecule

• A molecule is a group of two or more atoms chemically bonded together.
• Molecules can be composed of atoms of the same element (diatomic molecules) or different elements (polyatomic molecules).
• Molecules have a distinct chemical formula that specifies the types and numbers of atoms present.

Examples of Molecules:

• Oxygen molecule (O2): Oxygen gas consists of two oxygen atoms bonded together by a covalent bond.
• Water molecule (H2O): A water molecule consists of two hydrogen atoms and one oxygen atom bonded together covalently.

Compound

• A compound is a substance composed of two or more different elements chemically combined in fixed proportions.
• Compounds have a unique chemical formula that represents the arrangement and ratio of atoms.
• Compounds can be broken down into their constituent elements through chemical reactions, but the elements within a compound are always present in the same fixed ratio.

Examples of Compounds:

• Sodium chloride (NaCl): Table salt is a compound made of sodium (Na) and chlorine (Cl) atoms bonded together in a 1:1 ratio.
• Carbon dioxide (CO2): Carbon dioxide is a compound composed of one carbon (C) atom and two oxygen (O) atoms bonded together in a 1:2 ratio.