Question

how many valence electrons does this element have?

Explanation:

Step1: Identify the element

The element has 17 protons, so it is chlorine (Cl).

Step2: Recall electron - shell rules

Electrons fill shells in the order: 2 in the first shell, 8 in the second shell, and the remaining in the outer (valence) shell. Chlorine has 17 electrons. The first shell has 2 electrons, the second shell has 8 electrons, and \(17-(2 + 8)=7\) electrons in the outer shell.

Answer:

7