Mark the valence electrons. Chlorine, Cl, is an atom with 17 electrons. Chlorine is in Group 7A and is one of the halogens. The electron configuration for chlorine is 1s 2 2s 2 2p 6 3s 2 3p 5 . The valence electrons are seven in the 3s 2 3p 5 subshells.
Chlorine is an example of a p-block element.
Sketch an atom of beryllium-9. Indicate the number of neutrons and protons in the nucleus. Show the relative average distances out from the nucleus for the electron subshells. Identify the valence electrons. Tell whether or not this element is an s-block element.