According to this video there are 20 multivalent elements, and from the periodic table, I see 20, but according to multiple websites, including this, it says there are only 5. What am I not understanding? Are there 20 or 5? I want to know so I can memorize them. Also, are there any that aren't transition metals that are exceptions, i.e. non-metal multivalent? If so, may you please list them in your response?
Again talking about multivalent elements because I am learning ionic compounds, and these are part of it. Also, please keep high-level vocabulary to a minimum, I know some science vocabulary but i am only in grade 10.
Edit: I would like to add that i am referring to how many metals have roman numbers, i.e like Fe which has 2+ and 3+ charge both. are there more than 5 of these or are there 20?