How many electrons does a sodium atom have?

A neutral sodium atom has 11 electrons.12

This total corresponds to its atomic number of 11, which defines the number of protons in the nucleus and, in a neutral atom, the number of orbiting electrons. These electrons are distributed across the first three shells as follows: 2 in the K shell, 8 in the L shell, and 1 in the M shell.12

In terms of electronic configuration, this is represented as $1s^{2}2s^{2}2p^{6}3s^1$, or more simply as 2-8-1. The single electron in the outermost 3s orbital is known as a valence electron, which accounts for the high reactivity characteristic of sodium.12