Each atom has a nucleus made of protons and neutrons surrounded by orbiting electrons. Protons are positively charged, and electrons are negatively charged. Neutrons are neutral. ... One set of this compound, exactly two hydrogen atoms and one oxygen atom, makes a molecule.

Atom:

An atom is the basic unit of matter that consists of a nucleus and one or more electrons orbiting around it. It is the smallest particle of an element that retains the chemical properties of that element. Atoms are the building blocks of all matter, and they combine to form molecules.

Molecule:

A molecule is a group of two or more atoms held together by chemical bonds. It is the smallest unit of a compound that retains the chemical properties of that compound. Molecules can be made up of atoms of the same element or different elements.

Key Differences:

Composition:
- Atom: An atom is composed of a nucleus consisting of protons and neutrons, surrounded by electrons.
- Molecule: A molecule is composed of two or more atoms held together by chemical bonds.

Size:
- Atom: Atoms are incredibly tiny, with diameters ranging from about 0.1 to 0.5 nanometers.
- Molecule: Molecules can vary in size depending on the number and types of atoms they contain. They can range from small molecules like water (H2O) to complex molecules like proteins.

Chemical Properties:
- Atom: Atoms have specific chemical properties determined by the number of protons in their nucleus, which defines their atomic number.
- Molecule: Molecules have their own distinct chemical properties, which are a combination of the properties of the atoms they are composed of and the arrangement of those atoms.

Formation:
- Atom: Atoms are not formed by any chemical reaction; they are the fundamental particles that make up elements.
- Molecule: Molecules are formed through chemical reactions where atoms combine and share electrons to form stable structures.

Examples:
- Atom: Examples of atoms include hydrogen (H), carbon (C), and oxygen (O).
- Molecule: Examples of molecules include water (H2O), carbon dioxide (CO2), and glucose (C6H12O6).

Interaction:
- Atom: Atoms can interact with other atoms through processes such as bonding, sharing or transferring electrons, and forming compounds.
- Molecule: Molecules can interact with other molecules through various chemical reactions, such as breaking and forming bonds.

Summary:

In summary, atoms are the smallest particles of an element that retain its chemical properties, while molecules are groups of atoms held together by chemical bonds. Atoms are the building blocks of matter, and they combine to form molecules. Atoms are composed of a nucleus and electrons, while molecules can vary in size and composition. Atoms have specific chemical properties based on their atomic number, while molecules have their own distinct chemical properties based on the atoms they are composed of. Atoms are not formed through chemical reactions, while molecules are formed through the combination of atoms in chemical reactions.