During a chemical change, atoms are rearranged to form new substances, but they are not lost or gained. This is a fundamental principle of the Law of Conservation of Mass.

Here's why:

* Atoms are the basic building blocks of matter. They cannot be created or destroyed in ordinary chemical reactions.

* Chemical changes involve breaking and forming bonds between atoms. The atoms themselves remain intact, just in different combinations.

Think of it like building with Lego bricks. You can rearrange the bricks to build different structures, but you always have the same number of bricks.