* Atoms are not created or destroyed: This is the fundamental principle of the law of conservation of mass. In a chemical reaction, the atoms present at the start are still present at the end, just rearranged.

* Atoms are rearranged: Chemical reactions involve the breaking and forming of chemical bonds between atoms. The atoms themselves remain intact but change their partnerships to form new molecules.

* Bonds are broken and formed: The energy required to break existing bonds comes from the surrounding environment, and the formation of new bonds releases energy.

* New substances are formed: The rearrangement of atoms into new combinations creates new substances with different properties than the original reactants.

Analogy:

Imagine building a Lego structure. You have a set of individual Lego bricks (atoms) that you rearrange to create different models (molecules). You can break apart existing models and rebuild them into new ones, but you always have the same number of bricks (atoms) at the beginning and end.

Example:

The combustion of methane (CH4) with oxygen (O2) produces carbon dioxide (CO2) and water (H2O).

* Reactants: CH4 + 2 O2

* Products: CO2 + 2 H2O

The carbon, hydrogen, and oxygen atoms present in the methane and oxygen molecules are rearranged to form carbon dioxide and water molecules. The total number of each type of atom remains the same.