Here's why:

* Electronic Configuration: Sodium has an atomic number of 11, meaning it has 11 electrons. Its electronic configuration is 2, 8, 1. This means it has one electron in its outermost shell.

* Tendency to Lose Electrons: Sodium tends to lose this single outer electron to achieve a stable octet configuration like the noble gas neon (2, 8).

* Formation of Cations: When sodium loses an electron, it becomes a positively charged ion (Na⁺), with a +1 charge.

Therefore, the valency of sodium is +1, indicating its ability to form a single positive charge when it participates in chemical bonding.