* Why atoms combine: Atoms are most stable when their outermost electron shell is full. By combining with other atoms, they can achieve this stable configuration.

* Types of chemical bonds:

* Ionic bonds: Occur when one atom gives up one or more electrons to another atom. This creates oppositely charged ions that attract each other.

* Covalent bonds: Occur when two atoms share electrons. This allows both atoms to have a full outer shell.

* Metallic bonds: Occur between metal atoms, where electrons are free to move throughout the entire structure.

Here are some examples of how atoms combine:

* Sodium (Na) and Chlorine (Cl): Sodium loses an electron to become a positively charged ion (Na+), while chlorine gains an electron to become a negatively charged ion (Cl-). These ions attract each other and form an ionic bond, creating sodium chloride (NaCl), commonly known as table salt.

* Hydrogen (H) and Oxygen (O): Two hydrogen atoms share electrons with one oxygen atom to form a covalent bond, creating water (H2O).

* Copper (Cu): Copper atoms share their outermost electrons with all other copper atoms in a piece of copper metal, creating a metallic bond.

In essence, atoms combine to become more stable by sharing or transferring electrons to achieve a full outer shell. This process is called chemical bonding.