Atoms and molecules of different elements can combine chemically to form compounds. Here's a breakdown:

* Atoms: The basic building blocks of matter. They are made up of protons, neutrons, and electrons.

* Elements: Pure substances composed of only one type of atom. Examples: oxygen (O), carbon (C), hydrogen (H).

* Molecules: Two or more atoms bonded together. They can be made of the same element (like O₂, oxygen gas) or different elements (like H₂O, water).

* Compounds: Substances formed when two or more different elements combine chemically in a fixed ratio. Examples: water (H₂O), carbon dioxide (CO₂), sodium chloride (NaCl).

How it works:

* Chemical bonds: When atoms combine to form compounds, they share or transfer electrons, creating chemical bonds. These bonds hold the atoms together.

* Fixed ratio: The atoms of each element in a compound are always present in a specific, fixed ratio.

Let me know if you'd like more examples or want to dive deeper into the types of chemical bonds!