How do I calculate expanded valence electrons?

[Chenning Yang Dis3l]

I've got a question on Cl3- on midterm and I have no idea how to solve it.

[Victor Qiu 1C]

The Cl atom in the middle forms 2 single bonds, and it has 3 lone pair electrons. Thus, the answer should be 10 valence electrons.

[SamayaJoshi1A]

Just go backwards and count the valence electrons based on the levels. Make sure to know that s has 2, p has 6, and d has 10. Then you can literally count the squares on the periodic table.

[Sami Siddiqui 1J]

I can confirm that I got an answer of 10 electrons, as Victor had said earlier. There were two single bonds and three lone pairs in the central chlorine atom, so 5 * 2 = 10 electrons surrounding that chlorine atom. It can be confusing given that we associate one electron for a bond if we were to calculate formal charges, but that is only to exaggerate the covalent character of the bonds if anything.