* Physical Changes: These alter the form or appearance of a substance but not its chemical composition. Think of melting ice (water changes state from solid to liquid), cutting paper (changing its shape), or dissolving sugar in water (sugar molecules are dispersed but still sugar). The chemical makeup of the substance remains the same.

* Chemical Changes: These involve the formation of new substances with different chemical compositions. This happens when atoms rearrange themselves to form new bonds. Examples include burning wood (wood reacts with oxygen to form ash, carbon dioxide, and water), cooking an egg (proteins change structure), or rusting iron (iron reacts with oxygen to form iron oxide).

Compounds are formed when two or more different elements chemically combine in a fixed ratio. This chemical combination involves the breaking and forming of bonds, which is a chemical change.

In summary: Physical changes involve changes in state or form, while chemical changes involve the creation of new substances. Compounds are formed through chemical changes, not physical changes.