Here's why:

* Atomic Structure: Sodium (Na) has 11 electrons. Its electron configuration is 2, 8, 1. This means it has one electron in its outermost shell (valence electron).

* Tendency to Lose Electrons: Sodium wants to achieve a stable, full outer shell like the noble gases. It's easier for it to lose its one valence electron than to gain seven more.

* Formation of Cation: When sodium loses its one valence electron, it becomes a positively charged ion called a cation. The loss of one negative charge leaves a net positive charge of +1.

So, the sodium ion (Na+) has a +1 charge.