When sodium (Na) reacts with bromine (Br2), it undergoes a chemical reaction to form sodium bromide (NaBr). The reaction is a classic example of a synthesis reaction, where two or more substances combine to form a single product.

The overall chemical equation for the reaction is:

```

2Na(s) + Br2(g) → 2NaBr(s)

```

During this reaction, the sodium atoms lose their outermost electron (1 valence electron) and bromine atoms gain an electron each to achieve a stable electron configuration. This results in the formation of positively charged sodium ions (Na+) and negatively charged bromide ions (Br-).

The electrostatic attraction between the positively charged sodium ions and negatively charged bromide ions holds the sodium bromide compound together, forming a solid ionic compound.

The reaction is highly exothermic, releasing a significant amount of energy in the form of heat and light. This is because the energy released when sodium atoms lose electrons and bromine atoms gain electrons is greater than the energy required to break the bonds in the starting materials.

In summary, when sodium reacts with bromine, it undergoes a synthesis reaction to form sodium bromide, releasing heat and light.