Question: if an atom has 11 electrons how many electrons are in the valence shell?
Answer: So, sodium's 11 electrons are arranged this way: 2 electrons in the first "shell", 8 electrons in the second "shell"; and 1 electron (the valence electron) in the third "shell". We write this as 2.8. 1. The last number is how we know the number of valence electrons.