* Atoms are the fundamental building blocks of matter. They contain protons, neutrons, and electrons.
* Protons and neutrons reside in the nucleus of an atom and contribute almost all of its mass. Electrons are much smaller and contribute very little.
* Chemical reactions involve the rearranging of atoms. They break and form bonds between atoms, but they do not create or destroy atoms.
The Law of Conservation of Mass
This is a fundamental principle in chemistry. It states that in a closed system, the total mass of the reactants before a chemical reaction must equal the total mass of the products after the reaction. This is because the atoms are simply being rearranged, not destroyed or created.
Example:
* Reactants: Hydrogen gas (H₂) and Oxygen gas (O₂)
* Reaction: 2H₂ + O₂ → 2H₂O (Water)
* Products: Water (H₂O)
The total mass of the hydrogen and oxygen molecules before the reaction is equal to the total mass of the water molecules formed after the reaction.
Important Note:
* While the mass remains constant, the volume and density of substances can change during a chemical reaction.
* Some reactions might release energy as heat, light, or sound, which could affect the apparent mass, but the mass of the system, including any energy released, remains constant.
