Sodium (Na) and chlorine (Cl) are both highly reactive elements because they have unstable electron configurations. Here's how they combine to form a stable compound, sodium chloride (NaCl):

1. Electron Configuration:

* Sodium (Na): Has 1 valence electron in its outermost shell. It wants to lose this electron to achieve a stable, filled outer shell like the noble gas neon (Ne).

* Chlorine (Cl): Has 7 valence electrons in its outermost shell. It wants to gain 1 electron to achieve a stable, filled outer shell like the noble gas argon (Ar).

2. Ionic Bonding:

* Transfer of Electrons: Sodium, eager to lose an electron, gives its valence electron to chlorine.

* Formation of Ions: Sodium, having lost an electron, becomes a positively charged ion (Na+). Chlorine, having gained an electron, becomes a negatively charged ion (Cl-).

* Electrostatic Attraction: The oppositely charged ions (Na+ and Cl-) are attracted to each other due to electrostatic forces. This attraction holds them together in a strong ionic bond.

3. Formation of Sodium Chloride (NaCl):

* Crystal Lattice: The positively charged sodium ions and negatively charged chloride ions arrange themselves in a regular three-dimensional structure called a crystal lattice.

* Stability: The strong electrostatic forces within the crystal lattice stabilize the compound. The overall charge of the compound is neutral, with the positive and negative charges balancing each other.

In summary, the combination of sodium and chlorine results in the formation of a stable compound (sodium chloride) due to the transfer of electrons, the formation of oppositely charged ions, and the strong electrostatic attraction that holds the ions together in a stable crystal lattice.