Sodium becomes stable by losing one electron because it achieves a full outer shell of electrons, which is a very stable configuration for atoms. Here's why:

* Electron Configuration: Sodium (Na) has 11 electrons. Its electron configuration is 2, 8, 1. This means it has one electron in its outermost shell (the third shell).

* Octet Rule: The octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable configuration of eight electrons in their outermost shell.

* Losing an Electron: By losing its one valence electron, sodium becomes a positively charged ion (Na+). This removes the single electron in its outermost shell, leaving it with the electron configuration of 2, 8, which is a full and stable second shell.

Think of it like this:

Imagine the outermost shell as a box that can hold eight marbles. Sodium only has one marble in its box, making it unstable. By losing that marble, it empties the box and now has a full box below it, which is a more stable configuration.

This tendency to lose electrons and achieve a stable configuration is what drives sodium's reactivity and its ability to form ionic bonds with other elements.