Atoms are the tiny building blocks of everything around us. They are the smallest pieces of matter that still have the qualities of an element. Each atom is made up of three main parts: protons, neutrons, and electrons. How these atoms are structured helps us understand how they interact in chemical reactions.

Key Points:

1. What is an Element?

   • There are 118 known elements. Each element is made up of a specific type of atom.
   • For example, hydrogen has 1 proton in its atom, while carbon has 6 protons.

2. How Atoms Connect:

   • Atoms join together to make molecules using different types of connections called bonds.
   • The main types of bonds are ionic, covalent, and metallic.
   • Around 90% of stuff we find in nature is made of compounds formed by these bonds.

3. How Atoms Change:

   • When a chemical reaction happens, atoms get rearranged to create new substances.
   • According to the law of conservation of mass, the mass of what you start with (reactants) is the same as what you end up with (products).
   • This means that atoms aren’t lost or added, they just change form.

4. Understanding Ratios in Reactions:

   • The ratio of atoms is very important in reactions.
   • For example, in the reaction of methane burning ($CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$), 1 molecule of methane combines with 2 molecules of oxygen to create carbon dioxide and water.

In short, atoms are key to understanding how chemical reactions happen and how matter changes.